-NRLF
C E fl?0
GIFT OF
THE TRANSMISSION OF NERVOUS IMPULSES
IN RELATION TO LOCOMOTION
IN THE EARTHWORM
A THESIS SUBMITTED IN PARTIAL SATISFACTION OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
AT THE UNIVERSITY OF CALIFORNIA
MAY, 1917
The Transmission of Nervous Impulses
in Relation to Locomotion
in the Earthworm
John P. Bo vard
A thesis presented to the faculty of the
College of Letters and Science
in the
University of California
in partial fulfillment of the requirements
for the degree of
Doctor of Philosophy.
Approved by subcommittee in charge
. Chairman
Berkeley, California.
UNIVERSITY OF CALIFORNIA PUBLICATIONS
IN
ZOOLOGY
Vol. 18, No. 7, pp. 103-134, 14 figures in text January 7, 1918
THE TRANSMISSION OF NERVOUS IMPULSES
IN RELATION TO LOCOMOTION
IN THE EARTHWORM
BY
JOHN F. BOVARD
UNIVERSITY OF CALIFORNIA PRESS
BERKELEY
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UNIVERSITY OF CALIFORNIA PUBLICATIONS
IN
ZOOLOGY
Vol. 18, No. 7, pp. 103-134, 14 figures in text January 7, 1918
THE TRANSMISSION OF NERVOUS IMPULSES
IN RELATION TO LOCOMOTION
IN THE EARTHWORM
BY
JOHN F. BOVAKD
CONTENTS
PAGE
Introduction 104
I. Work of Friedliinder 104
II. Anesthesia experiments of Krukenberg 105
III. Work of Biedermann 105
Materials and methods 106
I. Materials 106
II. Methods 106
1. Biedermann 's method 106
2. Anesthesia method by ether and nitric acid 107
State of anesthetized area 107
The problem 108
Acknowledgments 108
Experiments with anesthetized worms 108
I. Free moving animals 109
II. The tension factor 109
III. Autotomy : Ill
IV. Free nerve preparations 112
1. Dissection experiments 113
2. Graphic records 114
3. Effects of stovaine 116
V. Limits of transmission 118
VI. Dependence on the nervous system for transmission 120
VII. Eate of transmission of locomotor impulses 122
VIII. Eate of transmission of giant fiber impulses 125
Theoretical considerations 128
I. Eeview of anatomy 129
II. Theory of reinforced stimuli 131
Summary 132
Literature cited .. .. 134
- • . "
~ ^ - *- •*
».
-
104 University of California Publications in Zoology [V<>L- 18
INTRODUCTION
The normal creeping movements of the earthworm proceed as fol-
lows. The first movement is a contraction of the circular muscles of
the first few segments. This causes an extension of the anterior end.
The chaetae now become directed backwards and take hold on the
substrate while the longitudinal muscles begin a contraction which
draws the next few segments forward. The circular muscles in each
segment contract, one segment after another beginning at the anterior
end and proceeding posteriorly. Immediately following the circular
muscle action the longitudinal muscles contract so that a wave of
extension followed by a shortening can be seen to traverse the whole
animal. After the first wave of muscular activity is well started
posteriorly another may be initiated and at any one time several of
these contraction waves may be seen in a normally creeping worm.
Some years ago Friedlander (1894) showed that in the normal
creeping of an earthworm the nervous system played only a small part.
When a section of the nerve cord containing ten to twelve ganglia was
removed, the movements of the parts of the worm were still perfectly
coordinated. The most important part of the activity was the ' ' pull ' '
which the contraction of each segment as the wave progresses gave to
the succeeding segments. The wave-like motion of the contractions
proceeding down the length of the animal was due, first, to the pull
of segments on each other, and, secondly, to the sequence of reflex
actions of the nerves in each segment, which are such that the longi-
tudinal muscles follow the contractions of the circular muscles. This
nervous mechanism is, according to Friedlander, concerned with each
segment alone, and there is no passage of impulses up or down the
cord. No attempt was made by him to analyze the matter of tension
or pull, or to determine whether coordination wrould proceed without
this factor.
In order to show that the nervous system was entirely secondary,
Friedlander cut a worm into two pieces and then joined these two with
a thread The creeping movements of the anterior piece gave the
necessary pull on the posterior piece through the thread, and the two
parts crept along in perfect coordination. In certain special cases,
when the nerve cord was destroyed for a short distance without tran-
section of the body, the parts anterior and posterior to the cordless
region moved together with perfect coordination. According to this
1918] Bovard: Nervous Impulses in the Earthworm 105
view, then, the nerve cord is supplementary and concerned only with
those short reflex paths which are mediated by a single ganglion.
Previous to the year in which Friedlander published his analysis of
the movements of earthworms, Krukenberg (1881) showed, in some
work on leeches, that the middle section of the animal could be
anesthetized with the result that the parts anterior and posterior to
this region still acted in perfect coordination. In these animals, how-
ever, the nervous system differs structurally from that of an oligo-
chaete. In leeches the nerves run from the anterior to the posterior end,
while in the oligochaetes the only long nerves are the giant fibers, the
other fibers in the cord being those of short neurones extending at
most from one ganglion to the next. The anesthesia in leeches affects
only the peripheral nerve endings, while the trunks connecting anterior
and posterior portions are not affected.
The more recent work of Biedermann (1904) becomes particularly
interesting, however, as it gives some new light on the function of the
nerve cord of the earthworm. In this work on the comparative physi-
ology of peristaltic movements he compares the locomotor action in
earthworms to the rhythmic movements found in smooth muscle.
Biedermann discovered that if worms were placed in seven per cent
alcohol for a few minutes until they became motionless and then the
middle region of several segments was anesthetized with nitric acid or
pure chloroform for a few seconds, the muscular activity of the sec-
tion was destroyed and all response to stimulus failed. He then had a
worm with active anterior and posterior parts connected through the
anesthetized area by a nerve cord. In creeping movements, the
anesthetized area, or dead area, acted as one piece. It transmitted
no rhythmic movements, while the posterior part still acted in perfect
coordination with the anterior part.
In further tests by Biedermann of the transmission of impulses
through the cord over more than one segment, he pinned such anes-
thetized specimens to a cork plate by needles through the dead mus-
cular area and found that the posterior part still moved in perfect
coordination with the anterior part. With regard to the limits of this
transmission through the cord, and the speed of the impulses, it is
stated in his paper (1904, p. 493) that the transmission often runs
2-3 centimeters in 4-5 seconds.
In the interpretation of these experiments Biedermann accepts the
theory proposed by Friedlander, except that in order to explain the
coordinated movements of posterior pieces when a certain part was
106 University of California Publications in Zoology [VOL. 18
anesthetized, it is necessary to assume that the impulses run through
the cord for a considerable distance rather than through one ganglion
as Friedlander supposed.
MATERIALS AND METHODS
Materials. — Several species of worm were used for these experi-
ments. The large garden worm, Helodrilus caliginosa, was favorable
material owing to its size. The small dung worm, Allolobophora
foetida, was also very convenient material because of the ease of
obtaining the material during the winter. No difference was observed
in the reactions in these worms. Unless specially noted the experi-
ments recorded will refer to the larger worm, Helodrilus.
Methods. — Biedermann's (1904) method of anesthetizing a cer-
tain portion of a worm by use of nitric acid or chloroform, as described,
had the effect of killing any peripheral nerve endings present in the
part and of impairing the muscle cells. It left the anterior and pos-
terior portions connected, however, by a functioning nerve cord, still
intact, except that no stimuli applied to the treated epithelium were
effective in setting up reflexes.
It was suspected by Biedermann that as locomotion took place the
posterior part was acting in coordination, not only because it was
connected to the anterior, as Friedlander might have supposed from
his string experiment, but that there was some real nervous influence
transmitted by the cord in the inert middle section. In order to test
this point fully, he pinned the middle anesthetized portion to a cork
plate to remove the factor of tension, when it was found that the
posterior portion still made movements coordinated with those of the
anterior piece. This established beyond a doubt that transmission
did take place over a longer section of the cord than the earlier in-
vestigators had deemed necessary and showed the more important part
played by the nervous system.
In developing a method of anesthesia to test farther the matter of
transmission, it seemed to me desirable to find some means of blocking
reflexes in the middle area,, and yet it was also quite necessary at the
same time to leave the muscle tissue and the central nerve cord intact,
only the peripheral nervous system being eliminated. The method
developed was quite different from that of Biedermann. The worm
was placed on a glass plate slightly moistened with water, so that it
was slippery. A small four-drahm homeopathic vial containing some
1918] Bovard: Nervous Impulses in the Earthworm 107
cotton soaked with ether, was then turned down over the worm so that
the mouth of the bottle covered the middle section of the worm. It
was possible to hold this in place over the squirming worm until the
middle part was anesthetized. Owing to the slipperiness of the plate,
the worm could get no hold and autotomy was very rare. When,
however, as occurred in early experiments, this method was tried on a
cork plate, autotomy of the anterior or posterior part was frequent
because of the hold the chaetae were able to take on the cork and so
the worm could pull itself in two. Exposure of two minutes to ether
fumes was sufficient for complete anesthesia, but had little effect on
the muscle tissue itself. The worms usually recovered completely from
the effects of the treatment in from ten minutes to an hour. During
this time a stimulus to the muscle in the anesthetized area called forth
a direct response but started no reactions in the untreated parts of
the worm.
In using some of the larger worms this simple method was varied
by treating the etherized area with six per cent nitric acid for ten
seconds, then washing the whole worm in water; this made certain
that the sensory nerve endings, of this part, were rendered functionless.
In cases where nitric aid was used the worm never recovered from the
treatment, and in a few cases where the worms were kept for a few
days they autotomized the posterior and middle sections. This method
was used where only a nerve bridge was desired between the active
anterior and posterior parts, as in measuring the speed of transmission
of impulses in the nerve cord.
STATE OF THE ANESTHETIZED AREA
For a very short period after treatment, the anesthetized section
looks whitish and gives off a great deal of mucous, but later the appear-
ance is much the same as that of the rest of the worm, except for an
increase in diameter. As the worm begins active movement, this
middle piece decreases in diameter, due to stretching, for it acts much
like a rubber band, extending and then contracting with each creeping
movement. However, no waves of muscular contraction run along
its length, as in the anterior and in the posterior parts, or from the
former to the latter.
Stimulation of a quiescent worm in the anesthetized and live
regions respectively gives a marked difference in response. If the
anterior part is touched lightly the response is an increase in diameter
due to a reflex stimulation of the longitudinal muscles, but a stimu-
108 University of California Publications in Zoology [VOL. 18
lation of the middle area results in a constriction, due to the contrac-
tion of the circular muscles with no reflex to the longitudinal muscles.
In recovery from the ether treatment the longitudinal muscles recover
and reassume normal functions first and the circular some minutes
later. In creeping movements the middle section shows that the
longitudinal muscles recover their nervous connection first, for they
begin to contract in coordination with the anterior part, some time
before the circular muscles begin any active participation in the
general movement. This condition is due no doubt to the fact that
the longitudinal muscles lie deeper than the circulars and so are less
affected by the anesthesia. In addition to this the position of the
longitudinal muscle is closer to the general blood supply, which would
be advantageous in the removal of waste products and the bringing
in of new materials.
THE PROBLEM
The problem then suggests itself : how is this transmission through
a number of segments accomplished? (1) Does Biedermann's dis-
covery necessitate the existence of long fiber tracts in the cord? or,
(2) Can it be explained on present knowledge of the neurones? (3)
Are there any limits to the transmission through anesthetized areas?
(4) Can the speed of such impulses be measured, and how do they
compare with the speed of nerve impulses in other annelids?
ACKNOWLEDGMENTS
The greater part of the experimental work was done at Harvard
University during the year 1914-1915, under the general direction
of Dr. G. H. Parker, to whom I am greatly indebted for his very
kindly interest and his many suggestions. Later the work of bringing
together the results of the experimentation was done at the University
of California. I wish to acknowledge and express my appreciation
for the helpful criticism and advice of Dr. S. S. Maxwell, of the
Department of Physiology, and to Dr. C. A. Kofoid, of the Depart-
ment of Zoology, for the general supervision of the work and the
revision of this paper.
EXPERIMENTS WITH ETHERIZED WORMS
Problem. — Will it be possible to get transmission of locomotor
impulses through an anesthetized area in both directions, from anterior
to posterior and also from posterior to anterior ?
1918] Bovard: Nervous Impulses in the Earthworm 109
Discussion. — If a worm is etherized by the vial method and allowed
to creep on a damp surface, such as moist filter paper, it will be seen
to act like a normal worm in every way, except that the middle or
etherized portion takes no part in the contractions. "With each pull
of the anterior piece it will stretch and passively contract as the pos-
terior piece moves up, without showing the normal waves of muscular
contraction seen in the active portions.
A worm, that is moving anteriorly, will reverse its direction and
creep posteriorly if stimulated on the anterior end. Stimulation of the
posterior end reverses the direction again. This indicates that nerve
impulses may pass up or down the nerve cord and that these impulses
may change the direction of the creeping movement, but it does not
indicate that the impulses responsible for the actual creeping pass
through the nerve bridge. There is still the fact that the muscles in
the etherized section attaching the anterior to the posterior part may
act as the "string" in Friedlander's experiment and give the neces-
sary pull which keeps the two parts working in coordination.
Conclusion. — These simple experiments only show that there may
be transmission of locomotor impulses in both directions through the
nerve cord in an anesthetized region of the worm.
TENSION
(a) Experiments with Etherized Worms
Problem. — To what extent is the factor of tension or pull respon-
sible for normal locomotor reactions?
Method. — By the use of ether in anesthesia we are able to test out
the importance of the matter of tension or pull in the transmission of
locomotor impulses. It will be remembered that the etherized part
acts as one piece. No waves of contraction pass up or down this part.
A small piece of cork was glued to a glass plate and the glass plate
kept wet. A worm prepared by etherizing ten segments in the middle
portion was pinned to the cork so that the anterior and posterior parts
were free to move, but the middle part was fixed.
Discussion. — Under these conditions no movements of the anterior
part could exert any pull on the posterior piece. In all such experi-
ments the worms behaved as Biedermann (1904) reported, the pos-
terior piece responding with locomotor reactions in perfect coordina-
tion to all attempts of the anterior piece to make creeping movements.
These movements could not be accomplished because of the slippery
110 University of California Publications in Zoology [VOL. 18
glass surface and the pinning down of the middle section, but the
wave of contraction, as in normal creeping, can be easily observed
(%. 1).
ABC
Fig. 1. This shows the method of pinning the anesthetized region of the
worm. Kegion A has just made an anterior creeping movement and region C
can be seen making a coordinated movement. On account of being pinned
through region B, the anterior part of C is forced to buckle.
The reversal of the direction of these movements is also possible.
Stimulation of the anterior end will cause the posterior end to attempt
creeping posteriorly with the anterior piece acting in perfect
coordination.
If, now, the nerve cord be severed in the middle region without dis-
turbing the muscular connections a great deal, the coordinated move-
ments of the two ends cease and become independent each of the
other. It is possible when a worm is pinned and the continuity of
nerve in the anesthetized area is broken, that the anterior and pos-
terior ends may each be making locomotor movements in opposite
directions, showing an independence of action even though joined by
a muscular connection. There can be, therefore, no doubt that the
nerve cord carries, for some distance, impulses which are responsible
for locomotor movements. By pinning the worm to the cork, the
matter of tension has been eliminated and by cutting the nerve, the
transmission through the nerve cord has been removed and coordinated
movements cease entirely.
AVhen such a worm with transected nerve cord and anesthetized
middle section is released from its cork plate and allowed to creep
freely, it is found that the coordination of anterior and posterior parts
is perfect. In this case, however, there is an entirely different
explanation. The coordination of the posterior end can not be due to
any nerve impulses from the anterior end, but each forward move-
ment of the anterior section causes a pull on the posterior piece and
this starts a chain of reflexes at the anterior end of the posterior piece
which run the length of this part of the worm and give rise to the
muscular contractions which normally would give rise to locomotion.
1918]
Bovard: Nervous Impulses in the Earthworm
111
In worms in which the entire dorsal wall, the lateral muscles, and
the intestine of the etherized part were dissected away and the nerve
cord freed from the ventral muscle by cutting the lateral roots, the
coordination continued perfect in function between the anterior and
posterior portions. It was observed that such specimens, in creeping,
did not move with the middle section tense, as a string connecting the
two parts, but that often the posterior part moved along rapidly,
causing the middle part to buckle so that under these circumstances
no pull could possibly have been exerted on the posterior part. When
the anterior part was pinned down, the posterior piece still continued
its coordinated movements and "telescoped" anteriorly into other
parts.
Conclusion. — Tension or pull, while important in normal creeping
movements, may be eliminated and the locomotor stimulus will still
pass on down the nerve cord for some distance.
(&) Autotomy
In the course of administering the anesthesia to the middle portion
of the worms, it sometimes followed that the strong contractions
would break the muscular walls of the body, a condition of incomplete
autotomy. If the animal was released in time the anterior and pos-
terior ends would remain connected by the intestine and the nerve
cord (fig. 2).
arvh posf
Fig. 2. This shows the nervous bridge as made in an incompletely auto-
tomized worm. The break in the musculature occurs between the segments.
The intestine (int.), with the dorsal and ventral blood vessels (d.bl.v. and v.bl.v)
and a portion of the ventral nerve cord (n.)} may be seen.
Problem. — Is the nervous bridge made by incomplete autotomy
between anterior and posterior ends of the worm capable of trans-
mitting locomotor impulses in both directions as in the etherized
worms ?
112 University of California Publications in Zoology [VOL. 18
Discussion. — Under these circumstances the reactions of the par-
tially autotomized worms are the same as in etherized ones; creeping
anteriorly and posteriorly can be induced by stimulation. If the
anterior end is pinned, the posterior part will still act in coordination ;
in this case the only possible way for the transmission to take place
would be through the nerve cord. Microscopical sections of such cases
as these showed that the nerve card was quite normal in structure and
still intact.
Friedlander (1894) laid such stress on the matter of tension, the
pull of one part on the next succeeding segment, that the behavior of
the worm under these conditions of anesthesia becomes particularly
important as bearing on the correctness and completeness of his
explanation (fig. 3).
Fig. 3. An illustration of Friedlander 's experiment which shows the anterior
and posterior parts of the worm tied together with a thread. The movement
of the anterior piece pulls on the anterior end of the posterior piece and starts
the locomotor reactions which are coordinated with those of the anterior half.
Conclusion. — In cases where the tension is eliminated by pinning
the worm to a cork on glass, the posterior part can be seen to begin
rhythmical movements of contraction coordinated with those of the
anterior part. If this anesthetized portion is composed of but few
segments, then the coordination is most perfect and the beginning of
the movement of the posterior section follows in shorter time than
when this portion of the worm includes many segments. It is possible
to anesthetize a section of such length that no coordination is carried
on and the posterior part lies entirely inert. In Helodrilus trans-
mission of impulses was effective through 20 segments, rarely through
28, and never through more than 30 segments.
NERVE FREE PREPARATIONS
Problem. — The fact that the worms perform autotomy and that the
anterior and posterior parts are then connected with each other only
by a simple nerve bridge and the intestine, suggested the possibility of
dissecting away all the connecting muscle between the anterior and
posterior parts. Could the nerve cord be dissected free for a distance
exposing several ganglia and could locomotor impulses be transmitted
through such a cord?
1918] Bovard: Nervous Impulses in the Earthworm 113
Methods. — (a) Dissection. All the muscle in the anesthetized
region was cut away after the worm had been pinned to a cork plate.
Owing to the fragility of the nerve, it was easily broken and in cases
where it was not broken it was easily impaired by stretching, so that
particular care had to be taken with the preparations made. Here,
as in the experiments discussed above, where transmission was over a
few segments, the coordination \vas good and as the nerve bridge was
lengthened the coordination was less complete and finally failed. Such
an operation must have a decided "shock" effect on the animal and
it does not behave as would be expected under more normal conditions,
consequently the length of the nerve does not represent the limits of
transmission, as will be shown in some experiments to be discussed
later.
In all these cases it was necessary to keep the worm pinned, for if
allowed free creeping the anterior part would move more rapidly than
the posterior, the nerve was not strong enough to drag the weight of
the posterior part and so the nerve was promptly broken.
In my first dissections all of the musculature in the anesthetized
region was removed, so that the nerve cord was the only connection
between the anterior and posterior parts of the worm. Later I modified
this so that the nerve cord, while entirely free for several segments,
was not allowed to touch the cork plate but was kept in its own body
fluids on a piece of muscle (fig. 4). All the muscle on the dorsal and
ar\{. \.r n. posf
Fig. 4. Type of dissection used in nerve free preparations, (n.) nerve cord
with lateral roots cut (l.r.), intestine (int.) and blood vessels (d.bl.v. and v.&Z.v.)
cut away.
lateral walls was dissected off. The intestine was removed. This left
the nerve cord attached to the ventral plate of muscle. A sharp flat
stylet was introduced under the nerve cord and all the lateral roots
severed. A transverse cut was then made across the ventral muscle
so that no muscular connection remained between the two parts of the
worm. "When this type of operation was used much more uniform
114
University of California Publications in Zoology [VOL. 18
results were obtained than where the nerve was allowed to come in
contact with the cork of the dissecting tray. Garrey and Moore (1916)
used a method similar to the earlier method that I used with the same
general results.
(&) Graphic Records. Apparatus. As a check on the observations
just described, it became desirable to find some way in which to make
a graphic record showing the part the nerve cord plays in the trans-
mission of locomotor impulses. The movements of the anterior and
posterior ends of the worm, while the middle part was fixed to a cork
plate glued on glass, suggested that if levers were attached to these
moving parts a record could be obtained on a kymograph. It was
necessary in order to obtain good records to have the levers as light
as possible and to have them move with very little friction. This was
accomplished by making the levers of aluminum wire, number 22. A
desired length was inserted in a cube of cork. Through the cork a
small glass capillary tube was thrust which made the bearing for the
axle of the lever. A very fine needle was then fitted into the glass
capillary and the needle stuck into a firm support. This sort of a
bearing allowed the lever to move with little friction and also was
Fig. 5. The general arrangement of the apparatus for recording movements
of the anterior and posterior parts of the worms. Method used at Harvard,
1914-1915.
a.l. — Aluminum wire lever connected to anterior end of worm by hook and
thread; c. — Cork plate glued to glass for pinning the middle anesthetized por-
tion; c.c. — Cork cubes through which aluminum wires run; g.pl. — Glass plate to
which a little water was added to allow the worm to slide back and forth when
pinned; p.l. — Aluminum wire lever connected to posterior end of worm by hook
and thread; Icy. — Drum of kymograph for taking tracings on smoked paper;
wt. — Counter balance weights.
1918]
Bovard: Nervous Impulses in the Earthworm
115
advantageous in that it allowed little side lash. Various forms of
levers could be built up by means of extra cork cubes and short sections
of aluminum wire, as in figure 5, a.l. and p.l.
The levers had to be weighted slightly so that the worm would be
kept in a straight line on the glass plate or else the curves recorded
would be exceedingly irregular (fig. 5).
If now a worm is prepared with the middle part anesthetized and
arranged to record movements, the movements of the posterior part
should show a perfect coordination with those of the anterior part
(fig. 6).
ant.
post.
Fig. 6. Experiment 143. A record showing perfect coordination between
anterior and posterior parts with a middle area of eight segments anesthetized
and musculature cut away. The upper curve represents the movements of the
anterior end and the lower that of the posterior end. Transmission of impulses
mediated through the nerve cord only.
The method of preparation of the middle portion varied. In some
cases the worm was treated with ether by the vial method, and then
triple-pinned to the cork plate. In other cases, in addition, the dorsal
musculature was cut away, the intestine removed, exposing the nerve
cord, and the lateral branches of the nerve cord transected. In still
other cases the musculature was cut in the middle region but not
116
University of California Publications in Zoology [VOL. 18
removed, so the nerve could rest on its own body fluids. In all these
cases coordinated movements of anterior and posterior portions were
shown. The best records were obtained when the least dissection was
used.
The clinching argument, however, was obtained when during the
course of such experiments the nerve cord is cut. In all such cases, no
matter what type of dissection was used, non-coordinated movements
were shown when the cord was transected (fig. 7) .
ant.
post.
Tig. 7. Experiment 143. Explanation of the curves here the same as in
figure 6. The nerve cord connection between anterior and posterior has been
cut. Notice the lack of coordination between the movements of two portions
of the worm.
(c) Stovaine. Should any doubts still remain concerning trans-
mission of impulses for locomotor movements over long sections of the
nerve cord, the action of stovaine will set these completely at rest. If
stovaine be injected into the body cavity of the worm it acts as a block
to the nerve cord over four or five segments and allows no impulses to
pass up or down through the segments containing the anesthetic. The
records will show that there is a lack of coordination and suppression
of movements of the posterior end while the drug is effective (fig. 8),
1918] Rovard: Nervous Impulses in the Earthworm
24 J 250
117
post.
time in
Vs sec.
ant.
Numbers refer to time of day animals were tested.
Arrow indicates stimulus given to the anterior end.
Fig. 8. Experiment 190. Stovaine injected into middle section of worm,
four segments affected. Lower curve registers the movements of anterior end
and upper curve those of the posterior end. At 2:41 P.M. the coordination
between anterior and posterior parts is not normal, and at 2:50 P.M. the giant
fiber action is lost. Stimulation at the arrow fails to give a reaction in the
posterior part. »
A represents ordinary locomotor activities.
B represents giant fiber action.
but as soon as the effects begin to wear off, the coordination between
the two parts becomes more and more complete until finally the
anterior and posterior parts are again acting in perfect rhythm (fig. 9) .
The supposition in this case is that stovaine acts on tissue of earth-
worm as it does in the vertebrates, where it has no effect on muscle or
nerve endings but acts only as a "block" on nerve fibers. The effects
of the drug were kept localized to small sections while anteriorly and
posteriorly all the normal reactions could be obtained.
Conclusion. — The nerve-free preparations, the graphic records of
movements before and after the nerve was cut, and the physiological
block established by stovaine, all go to show that the locomotor impulses
travel considerable distances in the cord. This work confirms the
results obtained by Biedermann but by quite different methods. The
most important aspect of these results is the demonstration that
118
University of California Publications in Zoology [VOL. 18
locomotor impulses are not "short relays" depending on a stimulus
from each segment, but are capable of running a number of segments
with no stimulus from the outside.
post.
time in
Vs sec.
ant.
A B
Fig. 9. Experiment 190. Continuation of experiment shown in figure 8. At
6:20 P.M. the worm had recovered from the effects of the stovaine. Normal
coordinated movements are being made (A) and the giant fiber action has
returned (-B). Stimulation of the anterior end at the arrow shows a response
in the posterior end.
LIMITS OF TRANSMISSION
Problem. — How far will these locomotor impulses travel in the
cord? Can a middle area of sufficient length be anesthetized so that
no impulses from the anterior piece can get through to start locomotion
in the posterior part?
Discussion. — It was soon discovered that transmission was best
shown when it was concerned with few segments and that, as the
number of ganglia through which the impulse must pass was increased,
the coordination became less and less perfect. No sharp limits could
be determined. When the nerve cord was dissected free from muscle,
the most severe type of dissection, the transmission seemed to be
limited to eight free ganglia. In one case, coordinated movements
were obtained when ten ganglia had been freed, but this was unique.
1918] Bovard: Nervous Impulses in the Earthworm 119
When the length of the free nerve contained four ganglia, transmission
was easily demonstrated.
In those cases where the dissection included the removal of the
dorsal wall, intestine, and the transection of lateral nerves, the trans-
mission easily ran for more than ten segments, but never for more
than twenty-eight.
It has been demonstrated by Biedermann (1904) and confirmed by
my own experiments, that the impulses run long distances in the cord
when the worms are anesthetized in the middle region which is after-
wards treated with six per cent nitric acid. In such cases, records of
transmission were obtained when twenty segments intervened between
the still active anterior and posterior ends. Failures came more often
as the length of this etherized part was increased. One record was
obtained with the large Helodrilus where coordinationed movements
appeared in the posterior part when twenty-eight segments were
etherized and their muscles killed with nitric acid.
These results fall somewhat short of the cases reported by Bieder-
mann, where coordinated movements were obtained through anes-
thetized parts two to three centimeters long, but the number of seg-
ments is not stated. The greater part of my records were obtained on
Helodrilus, where twenty segments of the body, in the part measured,
approximated two centimeters. While this does not show a great dis-
crepancy, my results are apparently nearer the lower figure quoted by
Biedermann.
We can establish, then, no absolute limits, except to say that trans-
mission is fairly well accomplished over ten segments, may run to
twenty and even to twenty-eight, but that the longer the nervous
bridge the greater the difficulty. No records have been obtained where
thirty segments were concerned.
One factor which makes the determination of any such records
very difficult is that impulses from normal stimuli in normal worms
starting down the length of the worm do not necessarily continue to
the end. The dying out of an impulse is quite a usual phenomenon
seen in the contraction waves that run only part way down the animal.
One of these impulses may start into the cord of the etherized part
and never reach the other end of the etherized part of the worm. This
does not mean that no impulses can come through, and so no limit can
be determined by this failure, but it does indicate a dying out of this
particular impulse somewhere in transit. Therefore, in the experi-
mental determination of the limits to transmission, as long as impulses
120 University of California Publications in Zoology [VOL. 18
come through the etherized part we are still within the limits of trans-
mission, but as soon as failures become frequent it is evident that the
limits have been approached. More refined methods may be able to
determine these limits closely. My records can be considered only as
approximations.
One other difficulty arises in making these determinations. Sum-
mation of stimuli has been shown by both Straub (1900) and Buding-
ton (1902) for annelid muscle. Weak stimuli adding themselves
together will sooner or later give a contraction. There is the possi-
bility that, in observations on these reactions, failures have been
recorded, where, in reality, weak stimuli did get through. However,
any errors so made would be on the conservative side.
Conclusions. — The results of these experiments show that no
absolute limits can be set, the impulses travel short distances in the
cord very readily and that the longer the section of cord to be traversed
the greater the difficulty. In Helodrilus twenty:eight segments was
the limit for the distance locomotor impulses would travel in the cord
when the superficial nerves were anesthetized.
DEPENDENCE ON NERVOUS SYSTEM FOR TRANSMISSION
Problem. — While the nerve cord is capable of transmitting loco-
motor impulses for considerable distances is it possible for the muscles
to carry on rhythmical movements without the aid of the nervous
system ?
Discussion. — If a short section of a worm containing about twenty
to thirty segments is prepared in such a way that it will give a record
of contractions of the longitudinal muscles on a moving drum, and the
lever is slightly weighted so the piece will be kept straight but not
stretched, it will be found to make rhythmic contractions. Straub
(1900) and Budington (1902) show this characteristic of annelid
muscle but disagree in the interpretation. Straub claims that strips
of the muscles, both with and without nerve, will give rhythmic contrac-
tions. However, regions of the worm from which the nerve had been
removed must be given several (eight) days for recuperation and then
they would give contractions comparable to those of the regions of
worm with nerve intact. Budington found that when care was used
to remove all nervous tissue by using only pieces of worm in which
the whole ventral muscle had been removed, that such pieces gave -no
rhythm ; while pieces containing even a small amount of nerve gave a
regular rhythmic curve (fig. 10).
1918]
Bovard: Nervous Impulses in the Earthworm
121
^-*>-AAM/U^
B
A = Short piece of whole worm with nerve cord.
B = Dorsal longitudinal half without nerve cord.
C ~ Ventral longitudinal half with nerve cord.
Fig. 10. Experiment 104. Curve A is made by a short piece of worm
attached to a writing lever. The piece was normal in every way and gave
rhythmical contractions. Curve B represents a curve made by the dorsal half
of a short piece of a worm that had been split in two longitudinally. This
piece contained no nerve cord. Curve C was made by the ventral half of a
short piece of a worm that had been split in two longitudinally. This piece
did contain the ventral nerve cord and did give rhythmic contractions.
My results agree entirely with those of Budington. It is quite
possible that the findings of Straub may be due to a factor that he
overlooked, the matter of regeneration. As I shall show in a later
paper, regeneration is exceedingly rapid and there is a possibility that
nerves have grown into the operated portion, and the probability is
that Straub was really dealing with pieces in which nerve fibers and
cells had regenerated.
As further evidence of this dependence upon the nerve cord for
transmission it will be noted that when a worm is pinned in the middle
portion to a cork plate and the anterior and posterior ends are regis-
tering coordinated movements on a revolving drum, if the nerve be
cut in the pinned region the rates of contraction of the two parts will
be immediately changed. In this case, the muscle is disturbed as little
as possible and only the nerve cord is cut (fig. 11).
Read in this direction — >
Fig. 11. Shows how the posterior half of the worm changed its rhythm after
the nerve cord had been cut. The upper line represents the movements of the
anterior (-4) half and the lower line the posterior (B) half. The nerve cord
was cut without cutting any but a small portion of the ventral muscle.
Conclusion. — From the work just cited, it is quite certain that
spontaneous movements are dependent on the nervous tissue and that
122 University of California Publications in Zoology [VOL. 18
the muscle has no property of rhythmic contractility. While this does
not show that transmission of impulse passes over many ganglia in
locomotion it strengthens the work of Biedermann (1904) and Bud-
ington (1902) who hold the theory of nervous control.
RATES OP TRANSMISSION OF LOCOMOTOB IMPULSES
Problem. — The fact that locomotor impulses could be transmitted
through a portion of the nerve cord isolated from segmental muscle
connections led to the query, what is the speed of these impulses ? If
the speed were rapid it would mean that there were some fairly long
neurones in the cord, and if the speed were slow it could be interpreted
on the basis of short neurones and many synapses. This study should
throw some light on the structural basis of transmission.
Discussion. — Jenkins and Carlson (1903) measured the rate of
nerve impulses in several species of annelids. The rates were found
to be exceedingly variable, from 89 centimeters in Nereis sp. to 694
centimeters per second in Bispira polymorpha. The question these
investigators raised was whether they were dealing with simple con-
tinuous nerve fibers or with a very complex nervous tract. While the
anatomical connections of neurones in the cord have been worked out
to some fair degree of certainty, no long connections have been estab-
lished in the cord, except by the giant fibers. Jenkins and Carlson
left the question open as to whether their measurements were those of
a direct nervous path or an indirect one.
After observing a very large number of experiments on the trans-
mission of the impulses as they pass through the etherized section of the
worm, and noting the slow progress of these as compared to the quick
end to end jerk of the worm when stimulated, there is little doubt
in my own mind but that the cord has two kinds of transmission of
nerve impulses. First, the very rapid impulses through giant fibers,
which result in vigorous contractions, as in the jerking back into their
burrows of the worms when strongly stimulated ; and the second type,
the impulses in the short fibers in the middle of the nerve cord, which
offer a complex path and so transmit impulses slowly down the cord.
My records for the speed of impulses in the giant fibers agree quite
well with the speed recorded by Jenkins and Carlson (1903). The
method which these workers used was such that only the action of
quick contractions was recorded and no attempt was made to separate
this phenomenon from that of the locomotor impulses. As has been
shown, these latter impulses run but short distances in the cord unless
1918]
Bovard: Nervous Impulses in the Earthworm
123
reinforced by outside reflexes ; and so, unless special methods are used,
the reactions of these short fiber systems would not be observed.
A frequent observation on the locomotor habits of worms is that
the wave of contraction runs for a short distance and then disappears.
This was a source of great inconvenience in determining the rate of
impulse down the cord. A method was devised whereby electric con-
tacts were successively made as the wave of contraction passed along
the worm. These were recorded on a drum from which measurements
were easily made and speeds computed (fig. 12).
ant
x. c.pl
Fig. 12. The apparatus for measuring the speed of nervous impulses through
the nerve cord in an anesthetized region was as follows: a.l. and p.l. are levers
pivoted at piv. The lower part of the lever n is a sharp, very fine needle. One
of these is thrust into the muscles of the first segment in front of the anesthet-
ized part m. and the other into the muscles just behind this region m. The
upper ends of these levers is quite long so that very slight movements of the
lower part will produce considerable movement in the upper part. Platinum
contacts were provided at pt.c. and each lever was connected by battery to
signal magnets, a.s. and p.s., which gave a record on a smoked drum of a
kymograph. When the locomotor movement of the anterior part of the worm
had reached the muscles at x. the electrical contact would be made in lever a.l.,
which registered on a fast revolving drum at a.s. Now when the nervous impulses
had passed through the anesthetized area m. and reached the muscle y. another
electrical contact was made by lever p.l. and registered by signal magnet p.s.
The speed of the drum being measured, the speed of the impulse could be
calculated.
124 University of California Publications in Zoology [VOL. 18
The very noticeable result of this series of experiments was the
great variability in the speed, which seemed to depend on the state of
irritability in the worm.
Another important fact seemed evident from these measurements;
namely, the longer the section of nerve measured the slower the rate
recorded.
TIME TAKEN TO TRAVEL OVER CERTAIN LENGTHS OF NORMAL AND
ANESTHETIZED WORMS
EXPERIMENT 180
EXPERIMENT 162 •
EXPERIMENT 162
1
1 3 live, 20 etherized
segments
.26 seconds
11 live, 20 etherized
segments
.90 seconds
19 live, 20 etherized
segments
.68 seconds
2
.44
.50
.65
3
.24
.64
.70
4
.21
.60
.90
5
.25
.34
.70
6
.35
.34
.82
7
1.02
.30
.92
8
.72
.25
.75
9
.13
.40
.72
10
.08
.25
.72
Average .370 .452 .760
1 These figures are calculated from experiment 180, a series different from
that in columns 2 and 3.
The method for making these records was not refined and the
times recorded can only be approximations. The table will show that
where the length of the portion of the worm measured is increased the
time of transmission increases, but not proportionately. The full
significance of this fact and its relation to transmission and a new
theory of locomotion will be brought out in a later part of this paper.
In measuring the speed of the impulse through the nerve cord in
a section where the muscle had been anesthetized, the electric method
of measurement was quite effective. Records of slight movements of
the segments just anterior to the inert section were followed by the
registration of movements beginning in the part immediately behind
this portion. Here again we meet great variability, depending on the
state of excitement in the worm. If the etherized section is greatly
increased in length the point will eventually be reached when no
impulse comes through. Records through more than twenty segments
were frequent, but when more than twenty segments were used, failure
resulted more often than in fewer than twenty. Measurements were
recorded over twenty-eight segments but these seemed to be exceptional
1918]
Bovard: Nervous Impulses in the Earthworm
125
cases. For the most part, impulses passed along the cord at the rate
of about 25 millimeters per second. This represents the mode of a
series of ninety-one measurements. Several observations showed good
transmission at the rate of 60 millimeters per second, and a few were
recorded in which the rate was very low, 10 millimeters per second
(fig. 13).
20,.
3 8
0 10 ZO 30 40 50 60 70 60 90 100 110
Fig. 13. The frequency polygon which shows results of ninety-one measure-
ments of the speed of locomotor impulses through the nerve cord when the
peripheral nerves have been anesthetized. The mode lies between 20 and 30
millimeters per second.
Conclusion. — The locomotor impulses show no definite speed. The
most interesting feature is the extreme variability of this movement.
In those cases where strength of stimulus is sufficient and other con-
ditions are right the speed may be as fast as 100 millimeters per
second, and again the speed may be so slow that it will ., die out in the
nerve cord without ever emerging from the anesthetized region. I
have taken the mode of the frequency polygon as against the average
which shows that ordinarily the speed is about 25 millimeters per
second. The slowness and variableness are the two main character-
istics.
RATE OP IMPULSES IN THE GIANT FIBERS
Problem. — How does the rate of transmission of locomotor impulses
compare with that of the giant fiber? Are the rates such that these
two phenomena can be ascribed to quite different systems of neurones ?
Discussion. — The method used to measure the rate of transmission
of impulses in the giant fibers was practically the same as that used
in measuring locomotor transmission, except that in this case it "was
126
University of California Publications in Zoology [VOL. 18
possible to use the full length of the worm. One characteristic of this
type of action is that it seems to be related solely to the longitudinal
muscles in contrast to that of the locomotor nerve fibers which set up
complex reactions in both circular and longitudinal muscles.
Responses resulting from stimulation of these large fibers are always
exceedingly rapid as compared with other movements of the worms.
The reaction may be slight or violent, according to the amount of
stimulus applied, but any response travels the length of the worm in
a very short time. It is interesting to note the antagonistic relations
of the innervation of muscles when a quiescent worm is stimulated
lightly, with a sharp needle, at the anterior end ; immediately there is
a response by a relaxation of the circular muscles near the posterior
tip so that this part is flattened and enlarged. If the stimulus is made
stronger, this reaction will be followed by a jerk of the longitudinal
muscle and when the stimulus is moderately strong the contraction of
the longitudinal muscle is so quick and extensive that no reactions
of the circular muscle can be detected.
A number of determinations for speed of this rapid action are
recorded in the accompanying table. The range of variation is large,
due in part at least to the methods of measurement and the inaccur-
acies of the apparatus (fig. 14).
1457
1404
1388
, | 4069 |
420
365
342
ZZO
990
77O
5E4
1049
1026
IO2O
1870
1606
(512
£915
2566
Fig. 14. Frequency polygon which shows the speed of impulse through giant
fibers. The figures represent millimeters per second. The mode is between 1000
and 1500 millimeters per second.
All of these measurements were made on the large garden worm,
Helodrilus caliginosa, and as nearly as possible under the same con-
ditions. The interesting feature of this array of figures is that they
are high compared to those obtained in locomotor transmission. Ordin-
arily they can be said to be fifty times faster, and may even be one
hundred times faster, than the other type of transmission. The
mode for these few measurements is around 1500 millimeters per
second. While this is not so rapid as some recorded by Carlson and
Jenkins (1903) (table 1), in measurements on marine annelids, it is
certain that it belongs in the same class of phenomena as they were
1918] Bovard: Nervous Impulses in the Earthworm 127
TABLE 1
SUMMARY OF RATES IN WORMS — CARLSON AND JENKINS
Species Direction Centimeters per sec.
Cerebratulus
P
A
5.4- 9.0
Aulastoma lacustre
P
A
56.0
Cirratulus sp
P
A
90.0
Arenicola sp
A
P
120.0
Bispira polymorpha
P
A
694.0
Aphrodite sp
A
P
54.0
Polynoe pulchra
P
A
293.0
Sthenelais fusca
P
A
205.0
Eunice sp
P
A
466.0
Nereis sp
P
A
165.0
Nereis virens
P
A
89.0
Nereis virens
A
P
73.0
Lumbriconereis sp. (a)
P
A
45-241.0
Lumbriconereis sp. (?>)
P
A
49-937.0
Lumbriconereis sp. (c)
A
P
42-160.0
Glycera rugosa
A
P
433.0
Glycera rugosa
P
A
435.0
measuring. None of my measurements approached the highest speeds
in these marine forms, such as that in Bispira polymorpha, viz., 6940
millimeters per second, or even in Lumbriconereis sp., viz., 9370 milli-
meters per second, nor on the other hand did I find any as slow as
that in Cerebratulus at 54 to 90 millimeters. Several worms, Nereis,
Arenicola, Sthenelais, give averages about the same as that which I
found for Helodrilus.
Jenkins and Carlson used averages in obtaining the figures above,
when it would seem such a variation in measurements occurred that
the mode is more nearly the correct expression. I have used this in
both series, that on locomotor transmission and on giant fiber action.
One feature of giant fiber action that is easily noticed is, that,
once started, it always goes through to the posterior end ; it never dies
out in transit as the locomotor waves do. In cases where the nerve
cord has been severed, the impulse runs as far as the cut, and never
beyond.
Krawany (1905) in his discussion of the elements in the central
nerve cord describes the relations of the giant fibers to the association
cells in the cord. These large fibers pass from end to end of the nerve
cord and in each ganglion send out branches which are intimately in
connection with processes from association cells in the middle group.
These cells which thus synapse with the direct fibers never have cross-
over connections but seem to be entirely homolateral.
128 University of California Publications in Zoology [VOL. 18
The physiology of these reactions is correlated with the anatomy
of these fibers. The path is a direct one and the speed of their
impulses is fast, 1500 millimeters per second compared with 25 milli-
meters per second for locomotor reflexes. The connections are simple
and the reactions are concerned largely with the contractions of but
one set of muscles, the longitudinal muscles. The fibers run the full
length of the cord and so reactions are concerned with the whole
animal. They are single fibers and produce a single action. There
is no wave motion nor evidences of loss as the stimulus passes down
the cord.
There is no reason to suppose that these fibers have anything to do
with locomotor reflexes or transmission ; everything points to a separate
function for these large long fibers.
Conclusion. — We have taken for granted that Friedlander 's (1894)
suggestion that the end to end movements are due to impulses carried
by the giant fibers. The results of this work on rates of transmission
seem to justify this supposition. No theory allows a nerve to have for
itself more than one rate of transmission. The speed of one type of
action and the slowness of the other would necessitate two kinds of
fibers. The anatomical conditions and the physiological reaction are
easily correlated. The large giant fibers are continuous structures
running the full length of the worm and capable of carrying the
impulses swiftly from end to end at a normal rate of 1500 millimeters
per second, while in the center of the nerve cord are numerous short
neurones running short distances up and down the cord, giving a
complex path, with slow speed of transmission, normally 25 milli-
meters per second, such as would be expected on account of the
multiplicity of synapses.
THEORETICAL CONSIDERATIONS
The Nervous Mechanism. — Some of the most salient facts brought
out in the study of transmission are: the nervous system plays an
essential part in the movements of locomotion; the impulses respon-
sible for the waves of contraction are capable of running for con-
siderable distances in the cord and are not confined to one or two
segments, as indicated by Friedlander ; transmission may extend over
as many as twenty segments without intervening muscular activity,
the rate of transmission is a variable one becoming slower as it pro-
1918] Bovard: Nervous Impulses in the Earthworm 129
ceeds. The giant fibers have little to do with locomotion and are
specialized for rapid, end to end contractions.
The excellent work of Krawany (1905) on the neurones of the
central system of the worm and the researches of Dechant (1906) on
the peripheral nervous system, together with the great amount of
work done by the older writers, such as Bethe (1903), Rhode (1887),
Apathy (1897), Retzius (1900), Biedermann (1904), Smirnow (1894),
and others, have demonstrated that the nervous system is compounded
of many short neurones. The longest elements are some few large
fibers from the anterior end of the cord which arise in the sub-
esophageal ganglion and run posteriorly to the terminal segment, but
Krawany (1905) shows that for the most part the other nerve fibers
run only from one ganglion to the next.
Sensory nerve fibers originating in the epidermis pass down
through the main nerve trunks to the ganglion where they branch as
T- or Y-shaped bifurcations immediately on entering. These run but
short distances before ending in fine arborizations. Krawany (1905)
was unable to demonstrate that these passed into ganglia anterior or
posterior to the segments of entrance, but was inclined to think that
they remained within the ganglion entered. No demonstration of
neuro-muscular end organs has ever been made in the smooth muscle
of earthworms. Retzius (1895) and Langdon (1900) have shown, by
using Golgi methods, that nerve fibers are in among the muscle cells,
but Dechant (1906) by using methylene blue was unable to differ-
entiate any definite end organs. Many nerve fibers parallel to muscle
can be seen, showing the presence of abundant nervous tissue, but all
fibers which looked like end organs proved to run only short distances
and could not therefore be true nerves. "While free sensory endings
in the subepithelial regions are not yet demonstrated, Dechant believes
they are undoubtedly there.
After entering the cord the sensory nerves bifurcate, one branch
passing up and another down the cord on the same side as they enter.
They may then form synapses with neurones of motor ganglia in the
anterior, middle, or posterior groups of nerve cells. These large cells
send out neuraxes which may or may not cross to the opposite side,
where they leave by one of the three lateral roots.
Within the cord, however, there are still other paths open to
impulses entering by the sensory paths. The large multipolar cells are
the association cells which show an arrangement into three groups, an
anterior, a middle, and a posterior group. Their function is to connect
130 University of California Publications in Zoology [VOL. 18
more or less distant parts of the ganglion and to interpolate them-
selves between the sensory and motor elements. Many of these are
homolateral and some are contralateral. The greater number of these
association cells are intraganglionic, i.e., never leaving the segment;
but a few in the anterior and posterior groups send processes into the
next ganglion and so connect up the ganglia segment to segment.
The most interesting feature is that in this nervous system there
are no long nerve tracts, the giant fibers excepted. Impulses that
run the length of the cord must find their way over a complex route
and be necessarily slow. We have then a nervous system made up of
many short units. Each ganglion is a complete relay station capable
of receiving sensory and giving out the motor impulses necessary for
the functions of each particular segment. The only connections
between the succeeding segments are association fibers in the nerve
cord and a few motor fibers which Dechant (1906) shows. These
motor fibers take their origin from a nerve arising from the posterior
root and pass laterally around the muscular wall near the interseg-
mental furrow and at intervals give off five branches which pass into
the segment behind. Without these two connections, one in the cord
and one peripheral, there would be no nervous connection from seg-
ment to segment of the worm.
Friedlander (1894) laid particular emphasis on the "pull" of one
segment on the succeeding ones and that coordination was accom-
plished even though the nerve cord were cut. The experiment of
cutting a worm in two and attaching a string to each part resulting
in coordinated movements indicates that pull certainly does play an
important part. Undoubtedly the tension or stretching stimulates
the nerve and starts the reflex movement. The succeeding movements
then are due to both pull and nerve impulse. If part is etherized, it
ceases contractions although it responds to direct stimulus. The nerve
reflex has been broken. Again, if tension be eliminated by pinning
experiments, coordinated movement proceeds ; but if now the nerve be
cut, coordination ceases. So while tension is important in supplying
a stimulus to the nerve mechanism, it is not wholly sufficient.
Biedermann (1904) showed that these reflexes can travel consider-
able distances in the cord. The interpretation of this might demand
that there be present in the nerve cord longer systems of neurones
than had been previously reported. However, it can be shown that
no such supposition is necessary. The present knowledge of th^
neurones can be used to explain the facts at hand?;
1918] Bovard: Nervous Impulses in the Earthworm 131
TRANSMISSION BY REINFORCED STIMULI
There is one other point of great importance in the analysis of
locomotion in the earthworms and one which has not been heretofore
mentioned. This is the variability in the rate of the impulse along
the cord. Experiments have shown that the transmissions over short
distances are much faster than those over longer distances, and this
agrees with a phenomenon easily observable in the movements of
worms, i.e., the dying out of waves of contraction. One can watch a
wave of contraction start down the length of the worm and become
more and more feeble until it is lost at the middle region. The distance
the wave runs seems to depend on the force of the wave at the start.
A strong wave runs further than one with a weak start. A glance back
at the charts of the speeds of impulses passing through the etherized
portion of a worm will show that there is a great variability. One
has but to observe a single worm under the experimental conditions
to become convinced of this without the figures.
Any theory that accounts for locomotion must take into considera-
tion the short unit system of the nervous system, the transmission of
locomotor impulses over long sections of the cord, and the variability
in rate of the speed of these impulses.
Friendlander (1894) likened the locomotor mechanism to a system
of telegraphic relays. Each contraction of the circular muscle elongated
the segment and stretched the longitudinal muscle. This stretching
caused a stimulus to pass along the nerves to the cord, where a reflex
gave a contraction of the longitudinal muscle. The contraction of the
longitudinal gave the pull which caused the circular muscle to contract
and so on down the length of the worm, each segment with its own
reflex, but progression of the wave of contraction due to the pull of
contracting parts on succeeding segments.
A short unit nervous system is all that is necessary for such an
explanation. But when transmission of locomotor impulses can pass
along the cord this relay system in each segment is not sufficient. If,
however, we suppose that the association fibers transfer stimuli from
one ganglion to the next, then we have a means for explaining Bieder-
mann's experiment. One of the characteristics of this transmission
was that it varied considerably in rate. • When the wrorm was in an
excited state or stimulated, the impulses passed through an etherized
section faster than otherwise. If we suppose that with each contrac-
tion reflexes are set up in each segment and that these stimuli entering
the cord reinforce the locomotor stimuli passing along in the short
132 University of California Publications in Zoology [VOL. 18
association tracts, and that if these stimuli are heavy they add to the
strength of stimulus passing along, or if weak add little or nothing at
all, then we have a basis for explaining the variations in rate. In
each ganglion there will be at least one and maybe two synapses to be
passed, each with a certain resistance which will tend to cu4; down the
force of the stimulus and its power to get through. Each synapse in
each segment resists the passage of the locomotor impulse but in
ordinary locomotion each well coordinated contraction wave reinforces
the loss and the movement runs the full length of the worm. The
uncertain limit of such transmission then can be understood for many
factors may come in to change the force of the stimulus ; the stimulus
may have started in a weak contraction — outside conditions may have
altered the amount of reinforcement — internal conditions in the cord
itself may have demanded a more complex path in one case than in
another, or even the physiological condition of the worm may have had
some effect on the resistance in the synapses.
SUMMARY
1. When a worm is anesthetized in the middle area and the peri-
pheral nerves are rendered useless, locomotor impulses may be trans-
mitted in both directions through the nerve cord of this middle region
from anterior to posterior, and posterior to anterior.
2. Tension or pull, while important in normal creeping movements,
may be eliminated and the locomotor stimuli will still pass up and
down the cord for some distance.
3. Nerve free preparations show that locomotor impulses may
travel considerable distances in the cord. Under such conditions the
anterior and posterior parts act in perfect coordination. When the
nerve is cut such coordination ceases. Stovaine when applied to the
nerve cord blocks the passage of locomotor impulses up and down and
the coordination of anterior and posterior parts is lost; as soon, how-
ever, as the effects of the drug are removed impulses again pass freely
in the cord and coordination returns.
4. The results of measuring the limits of transmission of the loco-
motor impulses shows that no absolute limits can be set. The impulses
travel short distances of ten segments very readily but when required
to traverse a longer section of twenty-eight segments the difficulty is
great. No records show impulses passing through as many as thirty
segments.
1918] Bovard: Nervous Impulses in the Earthworm 133
5. Spontaneous rhythmical movements are dependent on the
nervous system and the muscle tissues do not possess the property of
rhythmic contractility. This strengthens the theory that locomotion
is under nervous control.
6. The speed of locomotor impulses is quite variable. The mode
that expresses the normal rate is about 25 millimeters per second. The
rate may be increased or decreased in transit from segment to segment.
7. The rate of the transmission of giant fiber action is very rapid
when compared to that of the locomotor impulses. The mode for a
number of measurements shows the speed to be about the rate of 1500
millimeters per second. The wide gap between these two types of
nervous activity, the slow locomotor on the one hand and the rapid
giant fiber action on the other, indicates that these impulses are
mediated by two quite different kinds of nerve elements.
8. The anatomy of the nerve cord as shown by Krawany and
Deschant has in it no long neurones. The processes may join suc-
cessive ganglia but none extend through the cord for a great distance
except the larger giant fibers, which run the full length of the cord.
9. The peculiarities of the locomotor impulses in transmission, such
as the variability in rate of speed, and the slowness of it, can be
accounted for on the basis of the structure. The impulse to make its
way down the cord must pass in each ganglion at least one synapse,
and the possibility is that there would be more than this. Each synapse
would not only cut down the strength of the impulse but would also
slow down the speed because of the time consumed to cross the gap
between neurones. In normal creeping the impulses travel regu-
larly down the cord because each contraction of circular and longi-
tudinal muscle in each segment sends in locomotor impulses which
reinforce the impulse passing down the central nerve cord, and any
loss through the synapse is made up in this way. If for any reason
the muscular activity fail or if the nervous connections to the cord be
destroyed the locomotor impulse traveling down the cord in this region
would decrease in strength and decrease in rate because of the lack of
reinforcement.
134 University of California Publications in Zoology [VOL. 18
LITERATURE CITED
APATHY, S.
1897. Das leitende Element des Nervensystems und seine topographischen
Beziehungen zu den Zellen. Mitth. Zool. Stat. Neapel, 12, 495-748,
pis. 23-32.
BETHE, A.
1903. Allgemeine Anatomic und Physiologic des Nervensystems (Leipzig,
Thieme), vii, 487, 2 pis., 95 figures in text.
BlEDERMANN, W.
1904. Studien zur vergleichenden Physiologic der peristaltischen Bewegun-
gen der Wiirmer und der Tonus glatter Muskeln. Arch, gesam.
Physiol., 102, 475-542, 1 figure in text.
BUDINGTON, E. A.
1902. Some physiological characteristics of annelid muscles. Am. J. Physiol.,
7, 155-179, 16 figures in text.
DECHANT, E.
1906. Beitrage zur Kenntnis des peripheren Nervensystems des Begen-
wurms. Arb. Zool. Inst. Wien, 16, 361-382, pis. 1-2, 2 figures in
text.
FRIEDLANDER, B.
1894. Beitrage zur Physiologic des Centralnervensystems und des Bewe-
gungsmechanismus der Begenwiirmer. Arch, gesam. Physiol., 58,
168-206.
GARREY, W. E. AND MOORE, A. E.
1915. Peristalsis and coordination in the earthworm. Am. J. Physiol., 39,
139-148, 2 figures in text.
JENKINS, O. P. AND CARLSON, A. J.
1903. The rate of the nervous impulse in the ventral nerve cord of certain
worms. J. Comp. Neur., 13, 259-289, 14 figures in text.
KRAWANY, J.
1905. Untersuchungen iiber das Zentralnervensystem des Begenwurms. Arb.
Zool. Inst. Wien, 15, 281-316, pis. 1-15, 11 figures in text.
KRUKENBERG, C. F. W.
1881. Vergleichend-toxicologische Untersuchungen als experimentelle Grund-
lage fur eine Nerven- und Muskelphysiologie der Evertebraten.
Vergl. Physiol. Studien, 1, 77-155, 1 pi., 1 figure in text.
LANGDON, F. E.
1900. The sense organs of Nereis virens. J. Comp. Neurol., 10, 1-77, 3 figures
in text.
BETZIUS, G.
1895. Die Smirnow'schen freien Nervenendigungen im Epithel des Begen-
wurms. Anat. Anz., 10, 117-123, 7 figures in text.
1900. Zur Kenntnis des sensiblen und des sensorischen Nervensystems der
Wiirmer and Mollusken. Biol. Unters, 9, 83-96, pis. 16-22.
EOHDE, E.
1887. Histologische Untersuchungen iiber das Nervensystem der Chaeto-
poden. Zool. Beitrage, 2, 1-81, pis. 1-7.
SMIRNOW, A.
1894. Ueber freie Nervenendigungen im Epithel des Begenwurms. Anat.
Anz., 9, 570-578, 3 figures in text.
STRAUB, W.
1900. Zur Muskelphysiologie des Begenwurms. Arch, ges Physiol., 79, 379-
399, 15 figures in text.
UNIVERSITY OF CALIFORNIA PUBLICATIONS— (Continued)
5. Notes on the Tintinnoina. 1< On the Probable Origin of Diatyocysta tiara
Haeckel. 2. On Petalotricha cntsi, sp. nov., by Charles Atwood Kofoid.
Pp. 63-69, 8 figures in text. December, 1915 05
6. Binary and Multiple Fission in Har-amitus, by Olive Swezy. Pp. 71-88,
plates 9-11.
7. On a New Trichomonad Flagellate, Tricliomitus parvus, from the Intestine
of Amphibians, by Olive t Swezy. Pp. 89-94, plate 12.
Nos. 6 and 7 in one cover. December, 1915 .25
8. On Elcpltarcorys equi, sp. nov., a New Ciliate from the Caecum of the
Horse, by Irwin C. Schumacher. Pp. 95-106, plate 13. December, 1915 10
9. Three New Helices from California, by S. Stillmatt Berry. Pp. 107-111.
January, 1916 05
10. On'Trypanosoma triatomae, a New Flagellate from a Hemipteran Bug from
the Nests of the Wood Eat Ncotcma fuscipcs, by Charles Atwood Kofoid
and Irene McCulloch. Pp. 113-126, plates 14-15. February, 1916 .15
11. The Genera Monocercomoiias and PolymasUx, by Olive Swezy. Pp. 127-138,
plates 18-17. February, 1916 10
12. Notes on the Spiny Lobster (Pan-ulirus intcrrnptus) of the California Coast,
by Bennet M. Allen. Pp. 139-152, 2 figures in text. March, 1916 15
13. Notes on the Marine Fishes of California, by Carl L, Hubbs. Pp. 153-169,
platss 18-20. March, 1916 15
14. The Feeding Habits and Food of Pelagic Copepods and the Question of
Nutrition by Organic Substances in Solution in the Water, by Calvin O.
Esterly. Pp. 171-184, 2 figures in text. March, 1916 .15
15. The Kinetonucletis of Flagellates and the Binuclear Theory of Hartmann,
by Olive Swezy. Pp. 185-240, 58 figures in text. March, 1916 50
16. On the Life-History of a Soil Amoeba, by Charlie Woodruff Wilson, Pp.
241-292, plates 18-23. July, 1916 ; 60
17. Distribution of Land Vertebrates of Southeastern Washington, by Lee
Raymond Dice. Pp. 293-348, plates 24 26. June, 1916 60
18. The Anatomy of Heptanc.lms maculatus: the Endoskeleton, by J. Frank
Daniel. Pp. 349-370, pis. 27-29, 8 text figures. December, 1916 25
19. Some Phases of Spermatogenesis in the Mouse, by Harry B. Yocom. Pp.
371-380, plate 30. January, 1917 10
20. Specificity in Behavior and the Relation between Habits in Nature and
Reactions in the Laboratory, by Calvin O. Esterly. Pp. 381-392. JMarch,
1917 , : 10
21. The Occurrence of a Rhythm in the Geotropism of Two Species of Plank-
ton Copepods when Certain Recurring External Conditions are Absent, by
Calvin O. Esterly. Pp. 393-400. March, 1917 10
22. On Some New Species of Aphroditidae from the Coast of California, by
Christine Essenberg. Pp. 401-430, plates 31-37. March, 1917 35
23. Notes on the Natural History and Behavior of Emerita analoga (Stimpson),
by Harold Tupper Mead. Pp. 431-438, 1 text figure. April, 1917 .10
24. Ascidians of the Littoral Zone of Southern California, by William E. Ritter
and Ruth A. Forsyth. Pp. 439-512, plates 38-46. August, 1917 1.00
Vol. 17. 1. Diagnoses of Seven New Mammals from East-Central California, by Joseph
Grinnell and Tracy I. Storer. Pp. 1-8.
2. A New Bat of the Genus Myotix from the High Sierra Nevada of Cali-
fornia, by Hilda Wood Grinnell. Pp. 9-10.
Nos. 1 and 2 in one cover. August, 1916 10
3. Spclerpes platyceplwhtx, a New Alpine Salamander from the Yosemite
National Park, California, by Charles Lewis Camp. Pp. 11-14. Septem-
ber, 1916 05
4. A New Spermophile from the San Joaquin Valley, California, with Notes
on Ammospermophttus nelsoni nelsoni Merriam, by Walter P. Taylor. Pp.
15-20, 1 figure in text. October, 1916 05
5. Habits and Food of the Roadrunner in California, by Harold 0. Bryant.
Pp. 21-58, plates 1-4, 2 figures in text. October, 1916 35
6. Description of Bufo canorus, a New Toad from the Yosemite National Park,
by Charles Lewis Camp. Pp. 59-62, 4 figures in text. November, 1916...... .05
7. The Subspecies of Sceloporus occidentalis, with Description of a New Form
from the Sierra Nevada and Systematic Notes on Other California
Lizards, by Charles Lewis Camp. Pp. 63-74. December, 1916 10
8. Osteological Relationships of Three Species of Beavers, by F. Harvey
Holden. Pp. 75-114, plates 5-12, 18 text figures. March, 1917... .40
9. Notes on the Systematic Status of the Toads and Frogs of California, by
Charles Lewis Camp. Pp. 115-125, 3 text figures. February, 1917 10
UNIVERSITY OF CALIFORNIA PUBLICATIONS— (Continued)
10. A Distributional List of the Amphibians and Reptiles of California, by
Joseph Grrinnell and Charles Lewis Camp. Pp. 127-208, 14 figures in text.
July, 1917 85
11. A Study of the Races of the White-Fronted Goose (Anser albifrons) Occur-
ring in California, by H. S. Swarth and Harold C. Bryant. Pp. 209-222,
2 figures in text, plate 13. October, 1917 .15
Vol. 18. 1. Mitosis in Giardia Mieroti, by William C. Boeck. Pp. 1-26, plate 1. Octo-
ber, 1917 35
2. An Unusual Extension of the Distribution of the Shipworm in San Fran-
cisco Bay, California, by Albert L. Barrows. Pp. 27-43. December, 1917. .20
3. Description of Some New Species of Polynoldae from the Coast of Cali-
fornia, by Christine Essenberg. Pp. 45-60, plates 2-3. October, 1917 .20
4. New Species of Amphinomida,c from the Pacific Coast, by Christine Essen-
berg. Pp. 61-74, plates 4-5. October, 1917 .15
5. CritMdia fhiryophthalmi, sp. nov., from the Hemipteran Bug, EuryopMhalmus
Convivus Stal, by Irene McCulloch. • Pp. 75-88, 35 text figures. Decem-
ber, 1917 , 15
6. On the Orientation of Erythropsis, by Charles Atwood Kofoid and Olive
Swezy. Pp. 89-102, 12 figures in text. December, 1917 15
7. The Transmission of Nervous Impulses in Relation to Locomotion in the
Earthworm, by John F. Bovard. Pp. 103-134, 14 figures in text. January,
1918 - 35
8. The Function of the Giant Fibers in Earthworms, by John F. Bovard. Pp.
135-144, 1 figure in text. January, 1918 (In press)
9. A Rapid Method for the Detection of Protozoan Cysts in Mammalian
Faeces, by William C. Boeck. Pp. 145-149. December, 1917 05
UNIVERSITY OF CALIFORNIA PUBLICATIONS
IN ,
ZOOLOGY
Vol. 18, No. 8, pp. 135-144, 1 figure in text January 10, 1918
THE FUNCTION OF THE GIANT FIBERS
IN EARTHWORMS
BY
JOHN F. BOVARD
UNIVERSITY OF CALIFORNIA PRESS
BERKELEY
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IN
ZOOLOGY
Vol. 18, No. 8, pp. 135-144, 1 figure in text January 10, 1918
THE FUNCTION OF THE GIANT FIBERS
IN EARTHWORMS
BY
JOHN F. BOVAED
CONTENTS
PAGE
Introduction : 136
I. General functions of the nerve cord 136
1. Biedermann's theory 136
2. Muscle not responsible for rhythmic movements 136
3. Friedlander 's theory of giant fiber action 136
Materials and methods 137
I. Material used 137
II. Methods used 137
1. Simple transection 137
2. Eemoval of short sections of the cord 137
.3. Effects of the operation and recovery 138
Eegeneration experiments 138
I. Effects of simple transverse section 138
1. Eecovery of activity of locomotor fibers 139
2. Eecovery of activity of giant fibers 139
II. Eemoval of short pieces of the cord 140
1. Eecovery of locomotor fiber activity 141
2. Eecovery of giant fiber activity 142
III. Comparison of results with those of Straub and Friedlander 142
Experiments with stovaine 143
I. Methods 143
II. Eecovery from effects of drugs 143
1. Behavior of the locomotor fibers 143
2. Behavior of the giant fibers 143
Summary 144
Literature Cited .. 144
136 University of California Publications in Zoology [VOL- 18
INTRODUCTION
In the analysis of the locomotion of the earthworm Friedlander
(1894) showed that worms made well co-ordinated movements even
after considerable portions of their nerve cords had been removed.
He concluded that the nervous system served simply as a medium for
very short relayed reflexes and played a secondary part in locomotion.
Biedermann (1904) extended this idea by showing that stimuli could
run long distances in the cord, and in my recent paper (1918) I was
able to show something concerning the limits of this transmission and
also the rate at which such impulses travel in the cord when not
reinforced from without.
Straub (1900) claimed that the spontaneous contractions of short
sections of earthworm were due to inherent qualities of the muscle ;
at least they were not due to the nervous system present. My own
experiments seemed to show a contrary result, and in all cases rhythmic
movements were only in pieces containing nerve cord.
The results of these experiments just cited were obtained on worms
from which the nerve cord had been entirely taken away. It occurred
to me, therefore, to study the effects of regenerating nerve cord on
locomotor movements. It is well known that the nerves do not all
regenerate in the same time, and this, then, would give me some clue
as to which fibers carried locomotor responses and which the end to
end collapsing movements. Friedlander (1894) suggested that the
quick jerks which take the animal back into its burrow were due to
impulses carried by the giant fibers. This has been accepted as most
probable, but has not been demonstrated. If, then, a regeneration of
the nerve cord would give a differential healing, it would be probable
that the giant fibers would unite sooner or later than the transmission
nerves, and we would have some definite proof for Friedlander 's
contention.
The effects of simple transverse sections of the ventral cord were
studied and later short portions of the cord were removed. Drugs,
such as stovaine, were also tested, because they have the effect of
"blocking" the nerve cord, which is practically the same as removal
of ganglia for a brief time. Drugs have the added advantage of losing
their effect quickly, and so the changes in nerve reactions during
development and recovery from the anesthesia could be watched.
19183 Bovard: Giant Fibers in Earthworms 137
MATERIALS AND METHODS
Material. — Both the common Allolobophora foetida and Helodrilus
caliginosa were used in these experiments. Similar results were ob-
tained with each, but in general the larger worm was the easier to
work with, especially when operations were made for the removal of
sections of cord.
Methods. — In all cases where operations were to be performed the
worms were kept for at least twenty-four hours in clean moist cloths,
so they would clear themselves of dirt and grit. Worms that were
kept in moist filter paper usually ate large quantities of this, which
made the cutting of sections quite difficult.
The transecting of the nerve cord was a simple operation. The
worm was held tightly on a moist surface and a transverse cut made
with a safety razor blade. A single stroke was usually sufficient to
cut both ventral muscle and the nerve, and if care were exercised
there was little danger of cutting too deep. The cut was examined
with a hand-lens to make certain that the cord had been cut.
A simple physiological method of determining whether the cord
had been sectioned, and a method that proved a check on all experi-
ments, was as follows : Examination of the worm immediately after
the operation showed that the muscles posterior to the cut had lost
their tone, giving an increase in the diameter of the part. This con-
dition did not extend for any great distance, but was usually confined
to from three to five segments. If the nerve had not been severed,
this effect wore off after the first day of regeneration; otherwise it
remained enlarged until physiological continuity was re-established.
In operating on Helodrilus, a simple transverse cut with a razor
blade usually only severed the musculature. The cord adheres very
closely to the intestine and comes away from its ventral muscles very
readily. In these cases it was necessary to cut the cord with a pair
of fine scissors, making a simple snip. Where care was not used and
the ventral blood vessels were cut also, the animal bled profusely, and
in many cases died or autotomized the posterior piece.
When necessary to remove two ganglia, the worms were anesthet-
ized in a 5 per cent alcohol solution for fifteen minutes to one-half
hour, in all cases until they were motionless. Under a dissecting
microscope, a transverse cut was made in the ventral muscles. The
opening was stretched and pinned back with clean, fine needles. The
nerve cord and bloodvessels then could be easily seen. Great care
138 University of California Publications in Zoology [VOL. 18
had to be exercised to prevent cutting any blood vessels. The cord
was lifted up with fine forceps, and a cut made anteriorly. The cord
could then be pulled forwards and a cut made posteriorly. The seg-
ment, which was removed, was then put into 95 per cent alcohol and
examined later to ascertain the exact amount of nerve substance re-
moved.
After the operation the worms were placed in small 8-ounce jars
with some moist cloths over them and put away in a dark cabinet.
It was not found necessary to keep the worms in a particularly cool
place as long as the jars and cloths were kept scrupulously clean. The
temperature was the ordinary room temperature during April and
May in the Harvard laboratories. The only cases where worms died
during these experiments were those which bled profusely after the
operation due to rupture of the large ventral blood vessel. The loss
was surprisingly small.
By the following day the worms appeared normal, the wound had
healed over and they could be seen creeping about in the jars. Usually,
however, they were not very active in the cramped quarters of their
jars.
EFFECT OF TRANSVERSE SECTIONS OF THE CORD
The result of simply transecting the cord was the loss of trans-
mission and of the animal's power to reverse its direction of creeping
on stimulation. Stimuli applied at either end ran as far as the cut,
but failed to pass across the break in the cord. Earthworms often
respond to strong stimuli given to the anterior end by certain lashing
movements and side to side jerks. When the cord was severed these
lashing movements could be induced in the anterior portion of the
worm without producing any effect on the posterior part behind the
cut, which might lie quiet during this movement. Giant fiber action
induced either from the anterior or the posterior direction was effective
as far as the cut only. The quick, end to end action never succeeded
in starting the same kind of a movement in the portion of the worm
on the other side of the break opposite to the point stimulated.
The effects on the musculature were particularly noticeable. Im-
mediately behind the cut region the worm showed an enlargement of
the segments. Here the circular muscles seemed to have lost then
tone As the worm crept along the posterior part acted in co-ordi-
nation with the anterior, but these few segments behind the cut took
no part The length of this inactive part varies from three to five
1918] Bovard: Giant Fibers in Earthworms 139
segments. Behind this, normal creeping movements were seen as the
nerve regenerated and the lost function was restored. This appear-
ance of the cut region disappeared as the normal reactions returned.
REGENERATION
The regeneration of the nerve was remarkably rapid. Sections
of a worm (Allolobophora foetida) prepared after two days of regener-
ation showed that the nerve fibers had penetrated into the regenerating
tissue and had formed across the gap. And on the third day the
physiological reactions were being transmitted up and down the cord.
The reversal of the direction of creeping was easily possible on stim-
ulation. The giant fiber reactions, however, were not yet possible.
Any stimuli which called out such reactions in the anterior part of
the worm ran only as far as the cut, and the same is true of reactions
started in the posterior part. However, on the fourth day and fifth
day the giant fiber action was restored for the entire worm, which in
all respects gave normal reactions.
In the large Helodrilus, the same relations were found, except that
the period of regeneration was a little longer. The return of the
locomotor transmission occurred usually from the fourth to sixth day
after the operation and the giant fiber action on the following day.
The regeneration of nerve cord in this large worm shows a very inter-
esting thing in this return of the activity of the giant fibers. Twenty-
four hours after the return of locomotor transmission, one can look
for giant fiber action. This makes its first appearance as an impulse
traveling from anterior to posterior, and it is not until some hours
later, usually the following day, that this action is transmitted in the
opposite or postero-anterior direction.
In testing worms for the return of locomotor transmission through
the cut area it will be noticed that in the early stages posterior creep-
ing may not be the response on stimulating the anterior part. How-
ever, if several stimuli are given, summation takes place and a pos-
terior movement takes place. At other times the result of a stimu-
lation may be shown in the contraction of the circular muscles and
elongation of the posterior tip, a movement preparatory to creeping,
without the movement being completed by a well organized reaction.
The first indication of the return of giant fiber transmission is a
condition that shows the antagonistic innervation of muscles that has
been shown for vertebrates.
140 University of California Publications in Zoology [VOL. 18
The following table, no. 182, shows a series of worms and regen-
eration of nerve cord as expressed by the return of physiological
activity.
EXPERIMENT 182 — EEGENERATION OF NERVE CORD AFTER A SIMPLE TRANSVESE
SECTION
Time in days when impulses are again possible in Transmission Fibers and Giant Fibers
Worm
A
B
C
D
E
F
G
H
I
J
K
L
M
N
A P — transmission from anterior end to posterior end.
P A — transmission from posterior end to anterior end.
Stimulation of the anterior end causes the end to end jerk of
muscles as far as the cut, but behind this no such movement arises.
With each stimulus there will be seen, in the posterior tip, a relaxation
of the circular muscles and a dorso-ventral flattening. The chaetae
will be projected and directed forwards, but there is no movement of
the longitudinal muscles. A few hours later the same movement will
be accompanied by a distinct jerk of the longitudinal muscle, and the
next day a well co-ordinated, end to end contraction will be added to
the reaction.
REMOVAL OF SECTIONS OF THE CORD
When small sections of the cord were removed, as shown in the
following table, the return of physiological activity was in the same
order as when simple transverse sections were made. The time for
regeneration and complete recovery was lengthened, but was still sur-
prisingly short.
Locomotor
trans.
A P
Locomotor
trans.
P A
Giant
fiber
A P
Giant
fiber
P A
3
3
3
3
3
3
3
4
5
3
3
5
6
3
3
4
5
4
4
5
6
4
4
5
7
4
4
5
6
4
4
5
5
4
5
"s
10
4
4
5
5
5
5
6
6
5
7
10
5
5
6
8
1918]
Bovard: Giant Fibers in Earthworms
141
EXPERIMENT 191 — REGENERATION OF NERVE CORD AFTER REMOVAL OF SHORT
SECTIONS OF CORD
Giant
fiber
P A
9
11
6(1)9
9
13
6
11
6(?)9
Worm
No. of Trans,
ganglia locomotor
removed A P
Locomotor
trans.
P A
Giant
fiber
A P
A
2 6
6
9
B
11 4
4
10
C
2
Dead
....
D
21
Dead
....
E
H 4
4
5
F
2 4
4
9
G
11
Dead
H
1 9
9
12
I
H 4
4
5
J
1
Dead
K
1
Dead
....
L
2 9
9
10
N
2 4
4
5
A P refers
P A refers
to loeomotor impulses passing
to locomotor impulses passing
from anterior to
from posterior to
posterior,
anterior.
• j • .-,
- - int. epith.
n. sh.
g-.f.
-*-• — n. c.
ctx.
I. m.
cr. m.
ch. sh.
— spi.
Fig- 1 — A camera lucida drawing showing the union of the cut ends of the
ventral nerve cord. X 42. Experiment 191, line 1. In this worm two ganglia
had been removed and nine days given for regeneration. Normal locomotor
transmission and giant fiber action had returned, ch. sh., chaeta sheath; dr. m.,
circular muscle; ctx., cicatrix tissue; epi., epidermis; g. f ., giant- fiber; int. epith.,
intestinal epithelium; I. m., longitudinal muscle; n. c., nerve cord; n. sh., nerve
sheath.
142 University of California Publications in Zoology [VOL. 18
Figure 1 shows a longitudinal section of a worm that showed
normal locomotor transmission and giant fiber action after nine days
of regeneration. Two ganglia had been removed. In some cases the
regeneration was more rapid and in some slower, so this figure repre-
sents a typical case.
It was expected that the removal of short sections of the cord
would lengthen the time between recovery for locomotor transmission
and giant fiber action. But this was found not to be the case, for, in
general, the responses of end to end contractions recur about twenty-
four hours after the locomotor transmission reappears. Here, as in
the regeneration from simple transection, the giant fibers gave impulses
in the antero-posterior direction in advance of those in the opposite
direction. While removal of short pieces of cord lengthens that period
of regeneration in which no transmission of impulses is possible, it
changes very little the order and time of events after the union of the
cord is established.
The remarkable facility with which these worms regenerate lost
sections of nerve cord has an interesting bearing in the experiments
of Friedlander (1894) and Straub (1900).
After the removal of ten to twelve ganglia from the nerve cord,
Friedlander (1894) allowed the worm two to four weeks before he
discarded them for use in his experiments. My results would indicate
that he was not dealing with segments entirely free from nervous
transmission, for, while the nerve cord may not have entirely regen-
erated, it is certain that it could have grown considerable distances
into the region, even if it had not grown across the gap. This would
make a marked difference in interpreting experiments of co-ordination
of anterior and posterior pieces, especially if nearly four weeks had
been given for regeneration.
Straub (1900) claimed that annelid muscle would give rhythmic
contraction if the nerve cord were dissected out. In this case, sections
of twenty to thirty ganglia were removed and the worms given eight
days to recuperate. In this short time the nerve probably could not
grow the length of such a gap, but could grow into the area for a
considerable distance from the end of the nerve stump. When he cut
out the operated part and used this to show rhythmic contractions,
it is just possible these segments may have contained some regenerated
nerve elements. Budington (1902) has shown that segments of worms
containing even small fragments of nerve will give these rhythmic
contractions, but when the ventral wall is removed no such contrac-
tions can be induced.
1918 J Bovard: Giant Fibers in Earthworms 143
EFFECT OF DRUGS
If small quantities of cocaine or stovaine are injected into the
body cavity of the worm the drugs act as a block on the nerve and
affect the transmission through the nerve cord. Cocaine has a more
general effect on the worm and produces in many cases very irregular
behavior, but stovaine gives very consistent results. The first effect
was the loss of giant fiber action through the region. Transmission
was perfect above and below the point of injection. As the effect of
the drug worked deeper into the cord the transmission of locomotor
impulses became more irregular and in some cases was lost altogether.
As recovery took place the return of activity was just the reverse.
The locomotor impulses became more and more regular until perfect
co-ordination was set up. Then the giant fiber action began to show
transmissions. Here, too, the same phenomena were seen as in the
case of regeneration. Just before giant fiber impulses showed normal,
end to end responses, the stimulation of the anterior end showed the
characteristic relaxation of the circular muscles in the posterior tip.
Very soon after this the end to end movements occur in response to
stimuli.
A record is given below of an experiment with stovaine, which
shows the course of events and the relation between giant fiber and
locomotor fibers.
EXPERIMENT 188 — EFFECT OF STOVAINE ON TRANSMISSION
May 18, 1915, 4:45 p.m. — The worm (Helodrilus caliginosa}, doubly pinned to a
cork plate on a glass, was injected with a small quantity of stovaine in
the body cavity of the middle region.
Almost immediately giant fiber action is lost and locomotor trans-
mission not normal.
5:00 p.m. — Locomotor impulses pass through block, but do not run full length
of posterior part.
Locomotor co-ordination between anterior and posterior parts.
As time goes on locomotor movements run further down the posterior
part.
5:10 p.m. — Any stimulus to the anterior end results in locomotor movements
in posterior end. Wave contractions run to posterior tip more frequently.
No giant fiber action.
5:35 p.m. — Stimulation of anterior end gives increased activity of posterior
end. No giant fiber action. Animal apparently normal except no end to
end contractions.
5:48 p.m. — Giant fiber action returned. Animal fully recovered.
144 University of California Publications in Zoology [V<>L- 18
SUMMARY
1. After transverse section of nerve cord, locomotor transmission
fibers regenerate before giant fibers.
2. The period of regeneration after a simple transection is very
short, from three to four days.
3. Removal of short pieces of the cord gives the same results as
simple transverse section, except that the period of regeneration is
prolonged.
4. The effect of drugs, such as stovaine, on the cord shows that
the transmission fibers may be active, while the giant fibers are still
under the anesthetic. Recovery is in the same order as is shown in
regeneration.
5. The general result of this study shows that the giant fibers are
concerned with other functions than locomotion, and that locomotor
transmission fibers lie deep in the cord.
LITERATURE CITED
BlEDERMANN, W.
1904. Studien zur vergleichenden Physiologie der peristaltischen Bewegun-
gen. I. Die peristaltischen Bewegungen der Wiirmer und der Tonus
glatter Muskeln. Arch. ges. Physiol., 102, 475-542, 1 figure in text.
BOVAED, J. F.
1918. The transmission of nervous impulses in relation to locomotion in the
earthworm. Univ. Calif. Publ. Zool., 18, 103-134, 14.
BUDINGTON, B. A.
1902. Some physiological characteristics of annelid muscle. Am. J. Physiol.,
7, 155-179, 16 figures in text.
FRIEDLANDER, B.
1894. Beitrage zur Physiologie des Centralnerven systems und des Bewe-
gungsmechanismus der Eegenwiirmer. Arch. ges. Physiol., 58,
168-206.
STRAUS, W.
1900. Zur Muskelphysiologie des Eegenwurms. Arch. ges. Physiol., 79,
379-399, 15 figures in text.
UNIVEESITY OF CALIFORNIA PUBLICATIONS— (Continued)
5. Notes on the Tintinnoina. 1. On the Probable Origin of Dictyocysta tiara
Haeckel. 2. On Petalotricha entzi, sp. nov., by Charles Atwood Kofoid.
Pp. 63-69, 8 figures in text. December, 1915 05
6. Binary and Multiple Fission in Hexamitus, by Olive Swezy. Pp. 71-88,
plates 9-11.
7. On a New Trichomonad Flagellate, Trichomitns parvus, from the Intestine
of Amphibians, by Olive Swezy. Pp. 89-94, plate 12.
Nos. 6 and 7 in one cover. December, 1915 25
8. On Blepharcorys equi, sp. nov., a New Ciliate from the Caecum of the
Horse, by Irwin C. Schumacher. Pp. 95-106, plate 13. December, 1915 10
9. Three New Helices from California, by S. Stillman Berry. Pp. 107-111.
January, 1916 , 05
10. On Trypanosoma triatomae, a New Flagellate from a Hemipteran Bug from
the Nests of the Wood Rat Neotoma fuscipes, by Charles Atwood Kofoid
and Irene McCulloch. Pp. 113-126, plates 14-15. February, 1916 15
11. The Genera' Monocercomonas and Polymasti-x, by Olive Swezy. Pp. 127-138,
plates 16-17. February, 1916 10
12. Notes on the Spiny Lobster (Panulirus interruptus) of the California Coast,
by Bennet M. Allen. Pp. 139-152, 2 figures in text. March, 1916 15
13. Notes on the Marine Fishes of California, by Carl L. Hubbs. Pp. 153-169,
plates 18-20. March, 1916 .15
14. The Feeding Habits and Food of Pelagic Copepods and the Question of
Nutrition by Organic Substances in Solution in the Water, by Calvin O.
Esterly. Pp. 171-184, 2 figures in text. March, 1916 ,15
15. The Kinetonucleus of Flagellates and the Binuclear Theory of Hartmann,
by Olive Swezy. Pp. 185-240, 58 figures in text. March, 1916 50
16. On the Life-History of a Soil Amoeba, by Charlie Woodruff Wilson. Pp.
241-292, plates 18-23. July, 1916 60
17. Distribution of Land Vertebrates of Southeastern Washington, by Lee
Raymond Dice. Pp. 293-348, plates 24 26. June, 1916 60
18. The Anatomy of Heptanchus maculates: the Endoskeleton, by J. Frank
Daniel. Pp. 349-370, pis. 27-29, 8 text figures. December, 1916 25
19. Some Phases of Spermato genesis in the Mouse, by Harry B. Yocom. Pp.
371 380, plate 30. January, 1917 . 10
20. Specificity in Behavior and the Relation between Habits in Nature and
Reactions in the Laboratory, by Calvin O. Esterly. Pp. 381-392. March,
1917 10
21. The Occurrence of a Rhythm in the Geotropism of Two Species of Plank-
ton Copepods when Certain Recurring External Conditions are Absent, by
Calvin O. Esterly. Pp. 393-400. March, 1917 . .10
22. On Some New Species of Aphroditidae from the Coast of California, by
Christine Essenberg. Pp. 401-430, plates 31-37. March, 1917 .35
23. Notes on the Natural History and Behavior of JSmerita analog a (Stimpson),
by Harold Tupper Mead. Pp. 431-438, 1 text figure. April, 1917 10
24. Ascidians of the Littoral Zone of Southern California, by William E. Ritter
and Ruth A. Forsyth. Pp. 439-512, plates 38-46. August, 1917 1.00
Vol. 17. 1. Diagnoses of Seven New Mammals from East-Central California, by Joseph
Grinnell and Tracy I. Storer. Pp. 1-8.
2. A New Bat of the Genus Myotis from the High Sierra Nevada of Cali-
fornia, by Hilda Wood Grinnell. Pp. 9-10.
Nos. 1 and 2 in one cover. August, 1916 10
3. Spelerpes platycephalus, a New Alpine Salamander from the Yosemite
National Park, California, by Charles Lewis Camp. Pp. 11-14. Septem-
ber, 1916 05
4. A New Spermophile from the San Joaquin Valley, California, with Notes
on Ammospermophilm nelsoni nelsoni Merriam, by Walter P. Taylor. Pp.
15-20, 1 figure in text. October, 1916 .05
5. Habits and Food of the Roadrunner in California, by Harold C. Bryant.
Pp. 21-58, plates 1-4, 2 figures in text. October, 1916 35
6. Description of Buf o canorus, a New Toad from the Yosemite National Park,
by Charles Lewis Camp. Pp. 59-62, 4 figures in text. November, 1916 05
7. The Subspecies of Sceloporus occidentalis, with Description of a New Form
from the Sierra Nevada and Systematic Notes on Other California
Lizards, by Charles Lewis Camp. Pp. 63-74. December, 1916 10
8. Osteological Relationships of Three Species of Beavers, by F. Harvey
Holden. Pp. 75-114, plates 5-12, 18 text figures. March, 1917 .40
9. Notes on the Systematic Status of the Toads and Frogs of California, by
Charles Lewis Camp. Pp. 115-125, 3 text figures. February, 1917 10
UNIVERSITY OF CALIFORNIA PUBLICATIONS— (Continued)
10. A Distributional List of the Amphibians and Reptiles of California, by
Joseph Grinnell and Charles Lewis Camp. Pp. 127-208, 14 figures in text.
July, 1917 85
11. A Study of the Races of the White-Fronted Goose (Anscr albifrons) Occur-
ring in California, by H. S. Swarth and Harold C. Bryant. Pp. 209 222,
2 figures in text, plate 13. October, 1917 15
Vol. 18. 1. Mitosis in Giardia Microti, by William C. Boeck. Pp. 1-26, plate 1. Octo-
ber, 1917 35
2. An Unusual Extension of the Distribution of the Shipworm in San Fran-
cisco Bay, California, by Albert L. Barrows. Pp. 27-43. December, 1917. .20
3. Description of Some New Species of Polynoidae from the Coast of Cali-
fornia, by Christine Essenberg. Pp. 45-60, plates 23. October, 1917 20
4. New Species of Amphinomidae from the Pacific Coast, by Christine Essen-
berg. Pp. 61-74, plates 4-5. October, 1917 15
5. Crithidia Euryophthalmi, sp. nov., from the Hemipteran Bug, Euryophthalmus
Convivus Stal, by Irene McCulloch. Pp. 75-88, 35 text figures. Decem-
ber, 1917 15
6. On the Orientation of Erythropsis, by Charles Atwood Kofoid and Olive
Swezy. Pp. 89-102, 12 figures in text. December, 1917 15
7. The Transmission of Nervous Impulses in Relation to Locomotion in the
Earthworm, by John F. Bovard. Pp. 103-134, 14 figures in text. January,
1918 35
8. The Function of the Giant Fibers in Earthworms, by John F. Bovard. Pp.
135-144, 1 figure in text. January, 1918 10
9. A Rapid Method for the Detection of Protozoan Cysts in Mammalian
Faeces, by William C. Boeck. Pp. 145-149. December, 1917 05
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