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Thesis fer the Degree. 01‘ M. S.
Mlfifiifsm‘ SWE UNEVERSE‘E’Y
ROBERT G. SHERMM
1967

 

 

31:55::

   
 

  

LIBRARY

Michigan State
University

  

 

ABSTRACT

THE ORIGIN OF TH
YC

my?
UnOL

HEART BEAT IN THE SPIDER'
A

E
08 MISSOURIENSIS

 

by Robert G. Sherman

The cardiovascular physiology of spiders has been
little investigated. This study was undertaken to develop
methods for studying spider heart function as well as to ob-
tain information about the origin of the heart beat in the I
spider Geglycosa missouriensis.

Methods for recording the electrical activity of
both in gitg and isolated hearts were developed and were
used to determine the heart rate and its variability as well

as the type of electrocardiogram present. The mean i situ

 

heart rate was 145 beats per minute (inter-animal standard
error, 26 beats per minute; intra-animal standard error,

13 beats per minute). The mean isolated heart rate was 60
beats per minute (inter~animal standard error, 19 beats

per minute; intra—animal standard error, 8 beats per minute).

The electrocardiograms recorded from both in situ

 

and isolated hearts show the oscillatory electrical pattern
characteristic of neurogenic hearts.
A cord of tissue, previously unreported for any

spider heart and similar in location and appearance to the

Robert G. Sherman

cardiac ganglia of several other arthrOpods known to have
neurogenic hearts, is described.
On the basis of the anatomical findings and the type

of electrocardiogram, the heart of Q. missouriensis appears

to be neurogenic.

THE ORIGIN OF THE HEART BEAT IN THE SPIDER
GEOLYCOSA MISSOURIENSIS

By

Robert G. Sherman

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Zoology

1967

ACKNOWLEDGMENTS

The author wishes to express his appreciation to Dr.
Ralph A. Fax who directed this investigation and whose ad-
vice, criticism, and assistance has been invaluable during
this study. Grateful acknowledgment is also made to Drs.
Martin Balaban, Paul O. Fromm, and T. Wayne Porter who
served asxnembers of the author's guidance committee, to Dr.
Leslie C. Drew who identified the animal used in this study,
to Mrs. B. Henderson for her assistance in obtaining ma-
terials and to Mr. Charles R. Bursey for his photographic

assistance.

ii

TABLE OF CONTENTS

Page
ACMOWLEDGMNTS O O O O O O O O O O O I O O O O O O 0 ii
LIST OF TABLES O O O O O 0 O O O O O O O O O O O O 0 iv

LIST OF ILLUSTRATIONS O O O O O O O O O O O O O O O O V
INTRODUCTION 0 O O O O O '0 O O O O O O O O O O _. O O 1
Anatomy of the Spider Heart . . . . . . . . . . . 3
PhYSiOlogy Of the Spider Heart 0 o o o o o o o o o 1+
MATERIALS AND METHODS . . . . . . . . . . . . . . . . 7
Source and Maintenance of Animals . . . . . . . . . 7
HiStOlogical MethOdS o o o o o o o o o o o o o o o 7
Recording from Hearts lg Situ . . . . . . . . . . . 8
Recording from Isolated Hearts . . . . . . . . . . 8
DATA AND OBSERVATIONS . . . . . . . . . . . . . . . . 11
In Situ Heart Rates . . . . . . . . . . . . . . . . ll
ISOlated Heart Rates 0 o o o o o o o o o o o o o o 13
Anatomy of the Heart . . . . . . . . . . . . . . . l9
Electrocardiograms . . . . . . . . . . . . . . . . 25
DISCUSSION 0 O O O O O O O O O C O O O O O O O C O O 32
Recording Procedures . . . . . . . . . . . . . . . 32
Anatomy of the Heart . . . . . . . . . . . . . . . 3h
EleCtrocardiogramS o o o o o o o o o o o o o o o o 35
SWARY O O O O O O O O O O O O O 0 O O O O 0 O O O O 37
LITERATURE CITED 0 0 O O O O O O O O O O O O O O O O 39

iii

LIST OF TABLES
Table Page
1. Variability in IQ Situ Heart Rates . . . . . . . 12

20 variability in ISOlated Heart Rates 0 o o o o o 16

iv

Figure

l.

2.

3.

A.

5.

9.

10.

ll.

12.
13.

LIST OF ILLUSTRATIONS
Page

Heart Rate of an Intact Spider Showing Abrupt
Rate Increases o o o o o o o o o o o o o o o o 15

Heart Rate of an Intact Spider Showing Little
Variation in Rate . . . . . . . . . . . . . . 15

Heart Rate of an Isolated Heart Showing a
Gradual Initial Increase in Rate Followed by -
an Overall DeCline o o o o o o o o o o o o o o 18

Heart Rate of an Isolated Heart Showing Little
Change in Rate 0 o o o o o o o o o o o o o o o 18

Heart Rate of an Isolated Heart Showing a Steady
DeCline in Rate a o o o o o o o o o o o o o o 20

Methylene Blue Preparation of a Whole Heart
Showing a Cord of Tissue on Its Mid-Dorsal
Surface 0 o o o o o o o o o o a o o o o o o o ,22

Heart Stained in Hematoxylin and Eosin Showing
the Cord in Cross-seCtion o o o o o o a o o 0 2h

Heart Stained in Hematoxylin and Eosin Showing
the Cord in Cross-Section . . . . . . . . . . 2h

Heart Stained in Silver Showing a Cell Body and
Cell Processes in the Cord . . . . . . . . . . 27

Heart Stained in Silver Showing a Cell Body and
Cell Processes in the Cord . . . . . . . . . . 27

Heart Stained in Silver Showing a Group of Cell
Bodies in the Cord and Cell Processes that
Penetrate the Myocardium o o o o o o o o o o o 28

Electrocardiogram Recorded from a Heart IQ Situ 31

Electrocardiogram Recorded from an Isolated Heart 31

INTRODUCTION

Rhythmic heart contractions are initiated by the
endogenous activity of either muscle or nervous tissue. If
the initiation of the heart beat is due to nervous tissue,
the heart is said to be neurogenic. On the other hand, if
the heart beat originates in the heart muscle itself, the
heart is said to be myogenic. Hearts of vertebrates and
molluscs are myogenic, while those of arthrOpods, with
notable exceptions (e.g. Daphnia and some insects), are
neurogenic (Prosser and Brown, 1961).

The source of the activity initiating the heart beat
is called the pacemaker. Several indirect criteria may be
used to distinguish between the myogenic and neurogenic
nature of pacemakers (Prosser and Brown, 1961). The more
important ones are:

(l). The presence or absence of ganglion cells on or
in the heart. If present, the heart may be neurogenic; if
absent, the heart is probably myogenic.

(2). The pattern of the electrocardiogram recorded
from the heart. It is oscillatory in neurogenic hearts and
consists of large slow waves in myogenic hearts.

(3). Effects of certain drugs, particularly ether

and acetylcholine, on heart activity. Ether inhibits

l

neurogenic hearts and has little effect on myogenic hearts,
while acetylcholine inhibits myogenic hearts and may accel-
erate neurogenic ones. These criteria are, at best, only
indicators of the type of pacemaker present. In order to
conclusively determine the exact nature of the pacemaker,
one must identify the source of the endogenous activity and
show that it initiates the heart beat.

The pacemaker of bird and mammal hearts resides in
the sinoauricular node, while in lower vertebrates it is in
the sinus venosus. In molluscs, the heart beat may originate
at any point in the heart muscle. In forms having neurogenic
pacemakers, the heart has ganglion cells located either along
its dorsal surface or else just below the outer lining of
the heart. The best known examples of forms with this type
of heart are Limulus and the decapod crustaceans (Prosser
'and Brown, 1961).

Investigations into the initiation of the heart beat
in arthropods have been performed in detail in members of
only two classes, the Crustacea and the Merostomata (Limulus).
The cardiovascular physiology of the class Arachnida has
been little studied. The spiders are especially interesting
in this respect since many of them possess both book-lungs
and trachea. Thus the circulatory system of spiders appears
to be intermediate between the gill—respiring Crustacea and

Merostomata where it is essential for gaseous exchanges, and

the trachea-respiring Insecta where it apparently has little
or no respiratory function. Since cardiac function is tied
to the function of the circulatory system, a thorough study
of the circulatory system of spiders should be of special
value to comparative cardiovascular physiology. For this
reason and because there is very little information regard-
ing the functioning of this comparatively primitive heart,
I have investigated cardiac structure and function in the

spider, Geolycosa missouriensis. .

Anatomy of the Spider Heart
The structure of the heart of several spiders, in-

cluding the family Lycosidae of which 9. misgpuriensis

 

is a member, has been described in some detail (Petrunke-
vitch, 1910, 1922, 1933; Comstock, 1912; Millot, 1932, 19h9).
The heart of spiders is tubular and is situated mid-
dorsally in the anterior two-thirds of the abdomen. A
thin—walled pericardium surrounds the heart forming a
pericardial cavity. Suspensory ligaments attached to the
heart dorsally, laterally, and ventrally, hold the heart
in position. (Comstock, 1912).

The wall of the heart is composed of three layers.
These are: an outer layer of connective tissue, a thin
middle layer of lohgitudinal muscles, and a thick inner

layer of circular muscles. The muscles are transversely

striated. There is no inner lining of the heart. (Petrunke-
vitch, 1933).

A spider heart may have from two to five pairs of
ostia depending on the family of spider. In Lycosidae,
the heart has three pairs of ostia. Blood from the peri-
cardial cavity enters the heart through the ostia. From
the anterior of the heart, the main aorta carries blood to
the cephalothorax, while the abdomen is supplied with a
posterior aorta and three pairs of arteries. Blood from
the book-lungs is returned to the pericardial cavity by a
pair of pulmonary veins. (Comstock, 1912).

Information about the innervation of the spider
heart is lacking. Anatomical studies agree that abdominal
ganglia in adult spiders are absent, having migrated an-
teriorly during development to fuse with the subeSOpha-
geal ganglionic mass which is located in the cephalothorax.
(Petrunkevitch, 1933; Babu, 1965). A large pair of ventral
abdominal nerves from the subeSOphageal ganglionic mass
extend into the abdomen and have been described to give rise
to 12 branches which innervate many parts of the abdomen;
however, none were described to innervate the heart (Babu,
1965).

Physiology of the Spider Heart

Information about the cardiovascular physiology of

the spider heart is minimal. The electrocardiograms of

three genera of spiders (Empeira spp., Tarantula spp. and
Mygala spp.) were recorded by Rijlant (1933). He found that
each beat of the heart corresponded to a burst of 10 to 30
electrical oscillations lasting from 0.2 to 0.5 second,

with the first or second potential in the burst being the
largest. The frequency of the oscillations was from A0 to
100 oscillations per second. Solely from a comparison of
the electrocardiograms of these spiders with that of Limulus,
Rijlant concluded that the heart in these spiders is
neurogenic.

Heart rates of spiders are reported to range from
26 beats per minute (resting) in Liphistius desultor to
240 beats per minute (after exercise) in Micrommata virescens
(Bristowe, 1932). The heart of Tegenaria atrica is strongly
influenced by the central nervous system, since upon external
stimulation of this spider with bright light, abrupt in—
creases in its heart rate were seen (Mikulska and Kokocinski,
1965).

Epinephrine, when injected into the abdomen of
Tegenaria atrica, accelerates the heart rate and decreases
the amplitude of the beat, while acetylcholine produces a
slowing of the heart in addition to reducing the strength
of the contraction (Kadziela and Kokocinski, 1965). These
results are indicative of a myogenic heart. However, since

the drugs were injected into the abdomen of the spider,

there is no assurance that the effects seen are due to
effects of the drugs on the heart only and not on some other
tissues in the abdomen.

This thesis describes methods for monitoring heart
activity from both intact spiders and isolated heart prepara-
tions. Also included is new anatomical and physiological
information which indicates that the spider, Q. missourignsis,
possesses a cardiac ganglion and that the heart of this

spider is probably neurogenic.

MATERIALS AND METHODS

Source and Maintenance of Animals

Adult female Geolygosa missouriensis, 16 to 20 mm in
length, were used in all aspects of this study. The spiders
were collected in early spring and late summer from sandy
areas in the Rose Lake State Conservation Area located
about eight miles northeast of Michigan State University.
They were kept individually at room temperature in closed
two liter containers half-filled with sand. At weekly
intervals each spider was fed a cricket or a Galleria larva.
In this manner, spiders were kept for several months in

satisfactory condition.

Histological Methods

The following histological procedures were used to
prepare hearts for micrOSCOpic examination. Hearts to be
sectioned were fixed in Bouin's solution (Gray, l95t) in
gipg or after removal from the spider. Either serial cross-
sections (7 micra) or serial sagittal sections (10 micra)
were made. Satisfactory results were obtained by staining
the cross-sections with Harris's hematoxylin and eosin (Gray,
l95h) and the sagittal sections with silver following the
procedure of Samuel (l95h). Fresh hearts were stained in
methylene blue (Pantin, 19h8). 0n the whole, methylene

7

blue staining was unsatisfactory because of inconsistent

intensity of staining and precipitation of the stain.

Recording From Hearts I Situ

 

Recording from hearts ig gitg provides information
about how the heart functions inside the animal. For these
recordings, a spider was placed on a small piece of plywood
(5 cm by 5 cm) and held in position by drawing a sheet of
cheesecloth snugly over both spider and plywood. In this
way Spiders could be almost completely immobilized while the
spaces between the threads still provided direct access to
the dorsal surface of the abdomen for the placement of
electrodes for recording electrocardiograms. Insect pin
electrodes (size 000) were used and were placed on the
dorsal surface of the abdomen, directly over the heart.
Positioning of the electrodes was checked by the correlation
between the electrical activity and movement of the heart,
which was evident from the simultaneous movement of the
dorsal covering of the abdomen over the heart. Electrical
activity was amplified with a Grass P8 preamplifier and
displayed on a Tektronix 502A oscillosc0pe. The oscillosc0pe
trace was photographed with a Grass Ch oscillosc0pe camera.

All recordings were made at room temperature (2a to 26° 0).

Recording From Isolated Hearts
A fine analysis of cardiac function necessitates the

deve10pment of an isolated heart preparation in order to

experimentally control factors influencing the heart beat.
By using the following procedure, hearts were obtained which
continued to beat in isolation for as long as four hours.
The legs of the spider were removed to immobilize the
animal. The cephalothorax and abdomen were separated by
cutting through the pedicel and the isolated abdomen was
then placed in a Petri dish and covered with physiological
saline. The ventral portion of the abdomen was removed
and the viscera around the heart were teased away. Care was
taken not to remove the suspensory ligaments attaching the
heart to the abdominal wall. Thus, the isolated heart
preparation consists of the heart attached to the dorsal
abdominal exoskeleton by suspensory ligaments.

This preparation was placed ventral side up in a
V-shaped plexiglass dish partially filled with paraffin.
At this point, perfusion of saline over the heart was
begun and was continued at a rate of about 2 ml per minute
for the duration of the experiment. The electrical activity
of the isolated heart preparation was recorded by placing
insect pin electrodes (size 000) onto the exposed ventral
.surface of the heart. Permanent records of the electrical
activity were obtained by the same procedure used for re-
cording electrocardiograms from intact hearts.

Mechanical recordings were also made of isolated

heart activity. For these recordings, a fine thread was

10

tied to the movable arm of an E and M microdisplacement
myograph transducer connected to an E and M model four
physiograph. A bent piece of insect pin, fastened to the
other end of the thread, was gently pulled through the outer
lining of the heart. This attachment was made laterally
between the second and third pair of ostia, since this was
the region of greatest movement of the heart upon contrac-
tion.

The composition and pH of the saline used is as
follows: 117.0 QM sodium chloride, 5.0 QM potassium chloride,
h.0 QM calcium chloride, 1.1 QM magnesium chloride, and 3.0
QM sodium phosphate, at pH 7.3. This saline is a slight
modification of that described by Rathmayer (196;) for a
nerve-muscle preparation of the leg of the Spider Eurypelma
hentzi.. In Rathmayer's saline, sodium bicarbonate was used
in place of sodium phosphate as the buffer salt. In my
experience, the use of the bicarbonate introduced marked
changes in the pH of the saline. Changes in saline pH are
apparently detrimental to the isolated heart preparation,
since when using bicarbonate in the saline, successful prepar-
ations in which heart beating could be maintained for a period
of 20 minutes or longer were obtained in only 3 of 11 attempts.
In contrast, when an equal amount of phosphate was substituted
for the bicarbonate, successful recordings were made from six

of six isolated heart preparations.

DATA AND OBSERVATIONS

I Situ Heart Rates

 

The normal heart rate and its variability provide
a basis for making comparisons with the results of studies
involving changes in heart rates. For this reason, in nine
intact animals the heart rate and its variability were de—
termined from the electrocardiograms recorded from these
animals. The electrocardiograms ranged from 15 to AA minutes
in length.

The mean heart rate of the nine animals was 1A5 beats
per minute. The heart rate was not affected by the length
of the recording periods, since the average rate in the
last five minutes of the recordings was only 3 beats per
minute less than in the first five minutes.

Considerable variation in the rate was seen from
animal to animal. This is evident from the range in rates
(109 to 179 beats per minute)and the inter-animal standard
error which was 26 beats per minute. (See Table l). The
mean within-animal variability in rate was 13 beats per
minute (SE) which is much lower than that seen from animal
to animal. Two of the nine hearts exhibited considerably
higher variability than did the other seven hearts. The

within—animal variability in the rate of these two hearts

11

12

Table l. Variability in IQ Situ Heart Rates

 

L
T

 

Animal Mean Heart Rate 1 1 SE
No. (Beats Per Minute)
1 179; 20
2 122: 9
3 134: 12
4 1671 7
5 125.: z.
6 1371
7 1091.
8 1571 26
9 175: 11.
Inter—animal Standard Error 26
Mean Intra-animal Standard Error 13

 

was 23 beats per minute (SE) compared with 9 beats per
minute (SE) for the others. In the hearts displaying the
higher variability, occasional abrupt increases in heart

rate (up to 50 beats per minute per minute) were seen. Since
these spiders were observed to move at the same time that

the abrupt rate increases occurred, the increases were
probably due to struggling of the spiders against the re-
straining material. On the other hand, movement was also
occasionally seen without any increases in rate. About

five minutes after each abrupt rate increases, the heart rate

13

was back to the approximate level seen before the increase
occurred. The heart rate of a spider in which abrupt in-
creases in rate occurred is shown in Fig. 1. For comparison,
the heart rate of a spider in which little variation in

rate was seen (SE 4 beats per minute) is presented in Fig. 2.

Isolated Heart Rates

In order to determine whether spider hearts are
adversely affected by the isolation and monitoring pro-
cedures, a study of the heart rates of nine isolated heart
preparations was also made. The length of the recording
periods ranged from 21 to 120 minutes.

The heart rate and its variability were determined
in all nine hearts for the first 20 minutes of recording.
Their mean heart rate for this period was 60 beats per
minute, which is less than one-half that of the i3 gigg
hearts (1A5 beats per minute). As in the intact animals,
the isolated hearts showed a considerable variation in
rate from animal to animal. This is apparent from the range
in rates (39 to 100 beats per minute) and the inter-animal
standard error which was 19 beats per minute. (See Table 2).
However, the average intra-animal variation in rate was
only 8 beats per minute (SE). Here, as in the intact
animals, the intra-animal variation in rate is less than

the variation from animal to animal.

Figure 1. Heart rate of an intact spider in which abrupt
rate increases were seen. The arrows indicate
the minutes during which movement of the

spider occurred.

Figure 2. Heart rate of an intact spider in which little

variation in rate occurred.

15

m a W . w

upDZ_<< «um 34:

24

 

 

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II

N'N

Figure 1.

I20"

90%

332:2

>
0
6

man m—(un

30*

 

20

I6

I2

MINUTES

Figure 2.

16

Table 2. Variability in Isolated Heart Rates

W

 

Animal Mean Heart Rate 1 1 SE
No. (Beats Per Minute)

1 79: 3

2 67_+_ 6

3 100: 8

h 391 A

5 65_+_ 10

6 70: 14

7 653: 7

8 AS: 7

9 AA: 15
Inter-animal Standard Error 19
Mean Intra-animal Standard Error 8

 

In the first 20 minutes of recording, three general
patterns of isolated heart rates were observed. Five of
. the nine hearts showed a mean increase in rate of 21 beats
per minute from their average initial rate of 61 beats per
minute. This increase occurred gradually over the first
six to ten minutes of the recording period. These hearts
either maintained this higher rate (2 hearts) or else slowed
to a rate slightly below their initial rate (3 hearts). The
heart rate of one of these hearts is presented in Fig. 3.

Two of the nine isolated hearts displayed little change in

Figure 3. Heart rate of an isolated heart in which an initial
increase in rate occurred followed by an overall

decline.

Figure A. Heart rate of an isolated heart in which little

change in rate occurred.

BEAIS PER MINUIE

 

 

 

.
O

O

F o

b O

0
O
O
i»
O O
0
40> 0 o o

b

h

A 1 A 1 1 J 1 L L 1 I #4
20 40 60 80 IOO I20
MINUTES
.
Figure 3.
o o o
0 ° 0 o o
80* o o 0 o o o
o o o
o
o
o
60*

JJ

3

3

E

1

is 40

 

Figure A.

19

rate from their mean initial rate (65 beats per minute)
throughout the 20 minute period. The heart rate of one of
these hearts is shown in Fig. A. The remaining two isolated
hearts steadily declined an average of 2 beats per minute per
minute from their initial rate of 60 beats per minute. The
heart rate of one such heart is presented in Fig. 5.

Thus, over the first 20 minutes of recording, seven
of the nine isolated hearts did not show an overall decline
in rate with respect to time in isolation, while the other
two hearts did. Since no marked decreases in the heart
rate of these seven hearts were seen in the first 20 minutes,
recordings from these hearts were continued for an additional
period (up to 120 minutes). All seven hearts exhibited a
decrease in rate over time, with the decrease averaging 6
beats per minute for every ten minutes after the first 20
minutes of recording. Thus, these hearts also showed a
decrease in heart rate with respect to time, but the decrease

occurred only after the first 20 minutes in isolation.

Anatomy of the Heart
One criterion used to distinguish between the myogenic
and neurogenic nature of pacemakers is whether or not nervous
tissue is present on the heart. If nervous tissue is present,
the heart may be neurogenic. If nervous tissue is absent,
it implies that the heart is myogenic. Therefore an examina-

tion of 93 missouriensis was made to determine whether or not

20

MINUIE
O
0

40'-

bEAlS PER

L o
20 o

 

J I A J_ J J

p-
h

MINUIES

Figure 5. Heart rate of an isolated heart in which a

steady decline from the initial rate occurred.

21

nervous tissue is present on its heart.

I find that a cord of tissue similar in location and
gross appearance to the cardiac ganglion of scorpions
(Zwicky and Hodgson, 1965) and Limulus (Patten and Reden—
baugh, 1900; Carlson, 1904, 1905) is present on the dorsal
surface of the heart of this spider. Without the aid of
a microscope, this cord of tissue can be seen on unstained
hearts, but it is more easily seen on hearts that have been
stained with methylene blue (Fig. 6). The cord is located
in a mid-dorsal position and extends the entire 6 mm length
of the heart. It is widest anterior to the second pair of
ostia, where its diameter is about 50 micra. There is no
evidence of branching of the cord.

When serial cross-sections of the heart stained with
hematoxylin and eosin are examined microsc0pically, the cord
is seen to be rounded and to lie on the outer surface of
the heart. The cord is enclosed within a connective tissue
sheath. In several sections, ring-like structures up to 8
micra in diameter are seen within the cord (Figs. 7 and 8).
These structures are darkly stained with hematoxylin and
probably represent cell nuclei.

Sagittal sections stained with silver show the cord
to possess structural properties similar to those of the
cardiac ganglia of several other arthrOpods (Bullock and

Horridge, 1965). Within the cord are numerous cell bodies

Figure 60

22

 

1 mm

 

Methylene blue preparation of a whole heart
showing a cord of tissue situated on the mid-
dorsal surface. The anterior of the heart is

to the right.

Figure 7.

Figure 8.

Heart stained in hematoxylin and eosin showing

the cord in cross-section. The cord is situated
mid-dorsally on the surface of the heart, directly
under the pointer. Note the darkly stained ring-

like structure within the cord. (200 X).

Heart stained in hematoxylin and eosin showing

the cord in cross-section. The cord is situated
mid-dorsally on the surface of the heart, directly
under the pointer. Note the darkly stained ring-
like structure within the cord. (This section is
the same as that in Figure 7, but is magnified

860 X).

2h

 

 

Figure 8 .

25

from which arise typical neural-like processes (Figs. 9 and
10). These processes are seen throughout the length of the
cord. At about 12 different locations, some of the processes
leave the cord and penetrate the myocardium (Fig. 11). There
are at least 45 cell bodies in the cord. The diameter of

the cell bodies ranges from 20 to #0 micra. A majority of
them (about 30) are located in the cord anterior to the
second pair of ostia. Groups of three to four cell bodies
are often seen aligned closely together in the cord (Fig.
11), while others are seen positioned alone. Unfortunately,
sections of only one heart were carried through the silver
staining procedure to completion. Examination of a number
of other hearts by this method is needed before generali-

zations about the fine structure of the cord can be made.

Electrocardiograms

Another criterion used to distinguish between the
myogenic and neurogenic nature of pacemakers is that the
electrocardiograms of neurogenic hearts have an oscillatory
electrical pattern, while those of myogenic hearts con-
sist of large slow waves (Prosser and Brown, 1961). Thus,
the pattern of the electrocardiogram serves as an indica-
tion of the origin of the heart beat. In order to deter-
mine which type of pattern is present in Q. missouriensis,
electrocardiograms were recorded from both iQ gigg and iso-

lated heart preparations of this spider.

Figure 9.

Figure 10.

Heart stained with silver showing a cell body and
cell processes in the cord. The cell body is
located on the dorsal surface of the heart, at
the right of the photomicrograph. The wavy cell
processes extend posteriorly from the region of

the cell body. (Longitudinal section, A30 X).

Heart stained in silver showing a cell body and
cell processes in the cord. The cell body is
located on the dorsal surface of the heart,
directly under the pointer. Because of the
cutting angle, cell processes are seen only to
the left of the cell body and are extending

posteriorly. (Longitudinal section, 430 X).

27

 

Figure 9.

6

 

 

Figure 10.

28

 

 

Figure 11.

 

Heart stained with silver showing a group of
cell bodies in the cord and cell processes that
penetrate the myocardium. The cord is situated
on the dorsal surface of the heart, directly
beneath the pointer. Because of the cutting
angle, the cord ends near the left of the
photomicrograph. At least three cell bodies

are situated at the left of the cord. Near the
center, three cell processes leave the cord

and penetrate the myocardium. The space between
the cord and heart is lightly stained connective
tissue. (#30 X).

29

The electrocardiograms of both the QQ situ and iso-

lated hearts clearly show the oscillatory pattern charac-
teristic of neurogenic hearts (Figs. 12 and 13). The pattern
consists of a series of bursts of electrical activity, each
burst being characterized by an initial large potential
followed by a series of 7 to 25 smaller ones. The large
potential is from two to five times larger than the smaller
potentials. In isolated hearts, the duration of single
bursts ranges from 400 to 900 msec. and the frequency of

the activity in each burst varies from A0 to 80 oscillations
per second. In intact hearts, the duration of individual
bursts varies from 120 to 300 msec., with the frequency of
the electrical activity in each burst ranging from 20 to

55 oscillations per second.

Figure 12. Electrocardiogram recorded from an intact spider.
Thirteen bursts of electrical activity are shown.
Each burst represents one contraction of the

heart. Arrows mark the onset and end of a burst.

Figure 13. Electrocardiogram recorded from an isolated
heart. Two bursts of electrical activity are
shown. Each burst represents one contraction
of the heart. Arrows mark the onset and end

of a burst.

31

Andaman

0.1 my)

 

Figure 12. 1.0 sec.

 

 

DISCUSSION

Recording Procedures
Studies of cardiovascular physiology can be made
using two different types of heart preparations, i.e., hearts

in situ and those isolated and maintained beating apart from

—.

 

the animal. Each method has both advantages and disadvan-

tages. Studies of hearts in situ provide information about

 

the activity of the heart in normal operation inside the
animal, but do not permit manipulation of many of the factors
influencing heart activity. On the other hand, using iso-
1ated heart preparations, studies under controlled conditions
can be made, but there is no assurance that these controlled
conditions truly reflect the conditions present in the in-
tact animal.

The intact heart recording method described in this
study permits monitoring of heart activity for relatively
long periods of time without harming the animal. The only
manipulation of the spiders during the experiment involves
restraining them from moving. Since g. missouriensis nor-
mally remains motionless for long periods of time, I believe
that restraining this spider does not unduly influence
heart activity and that my recordings from intact animals
probably reflect the normal activity of g. missouriensis

hearts.

32

33

The isolated heart preparation developed in this
study provides a method for studying spider heart activity
under experimentally controlled conditions. The electro-
cardiograms of isolated hearts are essentially the same as
those recorded from intact hearts, indicating that the
initiation of the heart beat in intact animals and in iso-
lated hearts is probably the same. Although the normal
cycle is maintained in the isolated heart preparation,
there are obvious differences between the heart rate patterns

of isolated and 1Q situ hearts. These are:

 

(1). The isolated hearts show a decline in rate with

respect to time' hearts iQ situ do not.

(2). Abrupt rate increases occur in hearts 1 situ,

 

but never in isolated hearts.

(3). The isolated heart rates are much lower than

the rates recorded from hearts 1 situ.

 

The decline in isolated heart rates over time may be
due to the necessity for using an artifical physiological
medium. Although the physiological solution used in this
study is sufficient to maintain beating for as long as four
hours, it may not be sufficient to prevent a gradual decline
in the heart rate.

The lower isolated heart rates as well as the absence
of abrupt rate changes in the isolated hearts may indicate

that in the intact animal the heart is normally subject to

32+ .

central nervous system influence. This is supported by the

experiments of Mikulska and Kokocifiski (1965) who found that
the intact heart rate of the spider, Tegenaria atrica,
markedly and rapidly increases after shining a bright light
on the spider.

A number of other factors may contribute to the
overall lower isolated heart rate. The amount of tension
placed on the heart and the internal heart pressure are two
factors which have been shown to influence the heart rate
of isolated Limulus hearts (Carlson, 1907) as well as iso-
lated crustacean hearts (Maynard, 1960). Spiders are re-
ported to have a very high resting blood pressure (50 mm Hg
measured in a leg of the spider, Tengenargg atrica, by
Parry and Brown (1959)). The heart may be responsible for
the maintenance of this high peripheral blood pressure. If
this is true, one might expect the QQ gigg heart rate to be
higher than the isolated heart rate, since after isolation,

there is no peripheral blood pressure to maintain.

Anatomy of the Heart
The anatomy of the heart of Q. missouriensis is essen-
tially the same as that described in the introduction for
spider hearts in general. In addition, the heart of this
spider has a cord of tissue which has not previously been
described on the heart of any spider. The anatomical features

of this cord are similar to those of the cardiac ganglia
O

35

found in several arthropods with neurogenic hearts. Its
location on the heart is identical with the location of the
cardiac ganglion of scorpions (Zwicky and Hodgson, 1965)
and of Limulus (Patten and Redenbaugh, 1900; Carlson, 1904,
1905). The cord contains a number of cells identical in
appearance to the ganglion cells typically found in cardiac
ganglia (Alexandrowicz, 1926, 1932; Heinbecker, 1936). The
approximate number of these cells is intermediate between
the number found in crustaceans (up to 16) (Bullock and
Horridge, 1965) and Limulus (at least 100) (Heinbecker,
1936). The size range of the cell bodies (20 to A0 micra)
approximates the size of the multipolar cells in Limulus
(Heinbecker, 1936) and the small multipolar cells in the

spiny lobster, Panulirus argus (Maynard, 1953).

Electrocardiograms

The electrocardiogram of g. missouriensis is essen—
tially the same as those recorded by Rijlant (1933) from
Empeira spp., Tarantula spp., and Mygala spp. In my record-
ings and in those of Rijlant, the oscillatory pattern of
the electrocardiograms consists of a series of bursts of
electrical activity, each burst characterized by an initial
large potential followed by several smaller ones. Thus,
the electrocardiograms of the spiders that have been investi-
gated are similar to the electrocardiograms recorded from

other arthrOpods known to have neurogenic hearts, such as

36

Limulus (Carlson, 1904, 1905; Garrey, 1930, 1932; Heinbecker,
1933, 1936) and the decapod crustaceans (Maynard, 1953, 1955,
1960).

The anatomical evidence that the heart of Q.
Qissouriensis has a cord of tissue similar in location and
appearance to the cardiac ganglion of several other anthrOpods
and the type of electrocardiogram recorded from Q. missouri-
§Q§i§ indicates that the heart of this spider is probably

neurogenic.

SUMMARY

1. A procedure for recording electrocardiograms from
the 1Q giQQgspider, Geolycosa missouriensis, is described.

2. Procedures for recording both mechanical and
electrical activity of isolated heart preparations are de-
scribed.

3. The mean i situ heart rate is 145 beats per minute.

 

The inter-animal standard error is 26 beats per minute and
the range in rates from animal to animal is 109 to 179 beats
per minute. The intra-animal standard error is 13 beats
per minute.

A. The mean isolated heart rate is 60 beats per
minute. The inter—animal standard error is 19 beats per
minute and the range in rates from animal to animal is 39
to 100 beats per minute. The intra-animal standard error
is 8 beats per minute.

5. Electrocardiograms recorded from both 13 gigg and
isolated hearts have an oscillatory pattern characteristic
of neurogenic hearts.

6. A cord of tissue, similar in location and gross
appearance to the cardiac ganglia of several arthrOpods
known to have neurogenic hearts, is described for the heart

of Geolycosa missouriensis.‘

37

7. 0n the basis of the anatomical evidence and the
electrocardiogram, the heart of Q. missouriensis is probably

neurogenic.

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