V

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE
FART OF VOLUME XXXV :\

THE YOUNG OF THE CRAYFISHES
ASTACUS AND CAMBARUS

BY

E. A. ANDREWS

(No. 171

CITY OF WASHINGTON

PUBLISHED BY THE SMITHSONIAN INSTITUTION
1907

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE
PART OF VOLUME XXXV

THE YOUNG OF THE CRAYFISHES
ASTACUS AND CAMBARUS

BY

E. A. ANDREWS

(No. 1718)

CITY OF WASHINGTON
PUBLISHED BY THE SMITHSONIAN INSTITUTION

1907

,\v

I

Commission to whom this memoir has been referred :

WALTER FAXON
WILLIAM KEITH BROOKS
WILLIAM PERRY HAY

WASHINGTON, D. C.

PRESS OP JUDD & DETWEILER, INC.

1007

ADVERTISEMENT.

The present memoir by Professor E. A. Andrews, of the Johns Hopkins
University, on "The Young of the Crayfishes Astacus and Cambarus," forms
part of Volume XXXV of the Smithsonian Contributions to Knowledge.

The memoir describes and illustrates the young of two kinds of crayfishes,
one from Oregon and one from Maryland, which represent the two most
diverse forms found in North America. Of these, one genus, found only in
North America, is widely distributed all over the United States, except the Pa-
cific Slope; while the other is restricted almost exclusively to the Pacific Slope
in North America, and at the same time it is almost the only genus in Europe
and Asia. This memoir fills a gap in the knowledge of these common animals
that still remained notwithstanding the extensive researches of Huxley and
many others. •

It determines the form and habits of the first, second, and third larval
stages ; gives the first detailed description and illustrations of the appendages
of the first and second stages; describes the hitherto unknown nature of suc-
cessive mechanical attachments of the offspring to the parent; and opens up
the problem of the nature and causes of the incipient family life in the cray-
fish.

The new facts and comparisons add to the data for solution of the impor-
tant problems of the geographical distribution and the origin of the species
of crayfish, and they furnish a basis for practical application to the problems
of artificial culture and introduction of new kinds of crayfish.

In accordance with the rule adopted by the Smithsonian Institution, the
work has been submitted for examination to a commission consisting of Dr.
Walter Faxon, of the Museum of Comparative Zoology, at Cambridge, Mas-
sachusetts; Prof. W. K. Brooks, of the Johns Hopkins University, and Prof.
W. P. Hay, of Howard University, who recommended its publication in the pres-
ent series.

CHAS. D. WALCOTT,

Secretary.
SMITHSONIAK INSTITUTION,

WASHINGTON, June, 1907.

3

CONTENTS.

Page

I. Introduction 7

II. Historical 8

1 1 T. A status leniusculua 0

1. Introduction 9

3. Source of material 9

3. Care, food, habits, etc., of adults 10

4. Breeding 11

5. Development of eggs 12

G. Hatching 14

7. First larval stage: Sine; habits; appendages; relation to mother; telson

thread 16

8. Second larval stage: Size; habits; appendages 27

9. Third larval stage : Size; habits ; appendages 34

10. Fourth larval stage and later stages : Rate of growth 38

11. Comparisons with European Astacus 40

12. Bearing of artificial breeding upon possible acclimatization and economic

problems and upon geographical distribution 41

I V. Cambarus affinis 41

1. Introduction ; resume of breeding habits 41

2. Maternal structure for attachment of young 42

3. Hatching 43

4. First larval stage: Size; appendages; habits; relation to mother; telson

thread 43

5. Second larval stage: Size; appendages; habits; relation to mother, anal

thread 50

6. Third larval stage : Size ; habits ; tropisms 57

7. Fourth and later larval stages : Number of moults and rates of growth ... 63

8. Ratio of sexes ; sexual maturity 67

V. Comparisons and conclusions 69

5

The Young of the Crayfishes Astacus and

Cambarus.

By E. A. ANDREWS.

INTRODUCTION.

The object of the present paper is to figure and describe the external
forms and the appendages of the early larval stages of the crayfishes Astacus
and Cambarus and to illustrate the details of the connections that exist be-
tween these larva; and the mother.

It is well known that the genus Cambarus is found only in North America
and here only to the east of the Rocky Mountains, while the genus Astacus is
the only one found in Europe and Asia and in America is found almost ex-
clusively west of the Rocky Mountains. It is thus natural that the history of
scientific knowledge of crayfishes has been first the study of Astacus in Europe
and later the study of Cambarus in the eastern United States. The Astacus of
the Pacific States remains less well known.

Despite all the work that has been done upon these common animals,
several parts of their life histories have received scant attention. The geo-
graphical distribution and systematic description have been studied in detail by
Hagen, Faxon, Huxley, Ortmann, and others; the embryology minutely ob-
served by Rathke and by Reichenbach ; and the general knowledge of crayfish
natural history added to again and again since the days of Roesel von Rosen-
hof . Yet little attention has been given to the study of the young crayfish after
it leaves the egg; a comparative neglect that naturally arose from the centering
of scientific interest upon the larval changes of marine Crustacea in which re-
markable metamorphoses occur.

When these metamorphoses were established by Vaughn Thompson and
others it was already known from the work of Rathke that the crayfish hatches
from the egg in essentially the adult shape and thus passes through no series
of metamorphoses. Interest in the crayfish young was then restricted to the fact
that it was exceptional in having no metamorphosis. In the preoccupation of
students of crustacean life histories in study of metamorphoses the young of
the crayfish were left without any illustrations excepting only those given by
Rathke to show the condition of the embryo when nearly ready to hatch and the
two wood cuts given by Huxley. Theso latter illustrations were evidently

THE YOUNG OF THE CRAYFISHES ASTACUB AND CAMBABUS

.made from specimens preserved in alcohol, and, however excellent for their pur-
pose, fail to give the just proportions of the larva?, since all alcoholic specimens
of young crayfish are much swollen and distorted.

While two more figures of the young crayfish have recently been given,
(Andrews, '04) details of external structure are still lacking.

Having obtained the young of both Astacus and Cambarus by hatching the
eggs in the laboratory, it seemed well to fill in some of the gap in our knowledge
of the early larval life of crayfish, and especially so as the details of a curious
mode of connection with the parent were here first made evident.

HISTORICAL.

A brief statement of the history of our knowledge of the young of crayfish
will show that as yet the character of the appendages in the early stages, the
exact number of stages present in the life of the young while associated with
the mother, and the nature of the means by which the young are held attached
to the mother have waited discovery and illustration.

To Eoesel von Eosenhof belongs the credit of an enthusiastic appreciation
of the care of the mother crayfish for the young; the observation that the
young are transparent and like the parent; the description of their crowding
upon the abdomen of the parent and of their finally forsaking her after a few
clays, during which, however, they would return to her at times as if recalled by
a signal.

Eathke ('29) was chiefly concerned with the embryology of the crayfish, but
also described something of the growth in proportions and in internal anatomy
of the young after hatching and gave figures of the embryo and of some of its
appendages shortly before hatching.

Eeichenbach ('86) also added to his classic study of the embryology only
a figure of the abdomen of a recently hatched larva.

Soubeiran ('65) measured young crayfish grown at the farm of Clairfon-
taine and recorded their moultings and rates of growth. More facts of this
same kind were gathered by Chantran ( '70, '71) from prolonged study of larvae
reared in the laboratory of M. Coste. Chantran also discovered a peculiar fila-
ment that held the young to the egg-shell after hatching and he finally convinced
himself that the young ate their egg shells and their cast-off skins. Some
other observations upon the size and times of moulting of young crayfish in
Sweden were also made by Steffenberg ('72).

Huxley ('79) illustrated the recently hatched larvae by two wood cuts, one
showing the early larva fastened to the maternal pleopods by its peculiarly re-
curved claws, which he first described and figured, and the other a dorsal view
of such a larva. He rectified the previous statement that the young at hatch-
ing are exactly like the adult and pointed out their differences in lack of setae,

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS 9

in lack of abdominal appendages on the first and sixth somites, and in various
proportions.

In America Hagen ('70) in his fundamental study of our crayfish observed
the young of Cambarus attached to the mother in alcoholic specimens and re-
corded the dimensions of young in which the sexes were externally recogniz-
able. Prom like specimens Faxon ('85) in his revision of American crayfish
was able to make a number of comparisons with specimens of young Astacus
pallipcs from France, and also to demonstrate the important facts that the
young Cambarus agreed, in general, with Astacus as described by Huxley, but
that in the early larva as in the adult, Cambarus showed no vestige of the gill
found on the last thoracic somite in Astacus. These facts were verified by
Steele ('02), who for the first time described living larvae of Cambarus hatched
from eggs in the laboratory and also recorded facts as to the habits and sizes
of young larvae. From like living material Andrews ('04) added details of
hatching and behavior of these larvae with figures of side views of living larvae
in the first and in the second stages and noted the occurrence of two successive
attachments of the larva? by means of special structures.

To complete that last preliminary paper by adding details and many new
facts observed in Cambarus and to describe similar stages in our American
Astacus is the purpose of the present paper.

III. ASTACUS LENIUSCULUS.

As far as known, no observations have been made upon the life histories
and habits of any American crayfish of the genus Astacus and as the following
facts were gained from animals kept in Baltimore far from their native habitat
they will need the corroboration of future studies made in the Pacific States,
but for the present they supply all our knowledge of the young of American
Astacus.

The material for study of the young Astacus was obtained as follows : Sixty-
four specimens were received February 23, 1904, by express from Portland,
Oregon, and, though packed only in wet excelsior, ten females and eighteen males
survived the journey and lived in running water in the laboratory for some
time. Shipped without selection of sex, the sixty-four were found to be made up
of thirty-one females and thirty-three males, which indicates an equal distribu-
tion of the sexes. The males, however, seem to have endured the journey better
than did the females.

During March, April, May, and June these crayfish died slowly one by
one, leaving one survivor in October. As they were fed from time to time with
small oligochaatae, with fragments of crayfish and with pieces of frogs, the
cause of the very slow and lingering deaths was not evident, but probably the
food was not sufficient for such large and active crayfish.

2

10 THE YOUNG OF THE CRAYFISHES ASTAGUS AND CAMBAKUS

It was decided that this Astacus was probably Astacus leniusculus Dana
as distinguished from A. Trowbridgii by Faxon ('85) and the following observa-
tions upon their habits in captivity seem to be all that is known of this species,
beyond its specific -characters.

The largest specimen was a female measuring 155 mm. from tip of rostrum
to end of telson, 205 mm. from tip of chela to tip of telson, 40 mm. wide across
the thorax and 35 mm. deep; the abdomen was 45 mm. wide and its tail fan
expanded to a width of 70 mm., exclusive of the setae. With only about one-half
of its eggs left upon its pleopods this female weighed 106 grams.

The smooth clean shells and large well colored claws gave these crayfish
an attractive and decidedly lobster-like appearance, which was enhanced by
their very active pugnacious nature. In shallow water they quickly responded
to approaching objects and readily threw themselves into a defensive attitude,
leaning back with the whole anterior region raised high from the bottom of
the tank, thrusting their brilliantly colored claws above them high into the air
and either holding them wide apart and open or clashing them together towards
an approaching object, towards which they lunged, or even seemed to spring.

Their quickness to react to distant objects, their quick reflexes and irrita-
bility led me to suppose they might well be carnivorous and their clear colors
suggested a life in clear water, but the collector reported that the Willamette
River, whence they came, was a rather muddy stream, though formerly used as
water supply for Portland. In captivity they were nocturnal, lying quiet and
away from the lighter parts of the tank in the daytime and crawling about in
the night. They sometimes injured one another and also ate parts of their dead
fellow-crayfish and, as is so common with many kinds of crayfish, there were
cases of regeneration, which may have followed from injuries caused by their
pugnacious and carnivorous habits. One male 95 mm. long, when received, had
two regenerating limbs. The left chela was represented by its original basal
two segments and by a delicate new limb only 9 mm. long protruding from the
truncated end of the second large segment. This little, bluish protuberance
was made of six movable segments and it was movable upon the* old limb
whence it sprang, so that to make the seven normal movable segments of a
complete limb a reduction in the number of movable joints must take place,
probably by the base of the new growth ceasing to move upon the old second
segment. The other regenerating limb was the third left walking leg and here
again the old second segment bore a soft protuberance, which, however, was as
yet not segmented. Thus in this Astacus, as is common in other crayfish, re-
generations had started from the preformed breaking plane, and in handling this
same specimen, though dead, the right third walking leg fell off at the breaking
plane.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS 11

-

In captivity shedding, or ecdysis, took place in early summer, in some; thus
on June 11, when the water had risen from 9° C. in March to 22° C., one large
male cast its shell as one, perfect piece containing also the "teeth" and other
part of the lining of the "stomach." The creature was then quite soft and
easily indented by touch upon its carapace; it lay inert but could be made to
crawl in -a somewhat palsied way and even to flap its abdomen. On each side
of the heart region the carapace bore a white, indented, scar, as if made by
the claws of some other crayfish, so that the advantage of concealment at this
season as practiced by other Crustacea doubtless applies here as well. The
entire shell was covered by a slimy soft mucus and its colors were brighter than
before, the under side of the legs showing also more blue. As seen from be-
low, the flesh of the abdomen had a peculiar coagulated appearance.

The new carapace had a length of 57 mm. and the old of 43 mm., and had
enlarged in diameter from 25 to 28 mm. The cast shell had one broken antenna.
53 mm. long, which was replaced in the new shell by a perfect antenna 68 mm.
long. A week later tnis crayfish was active and keenly seized and ate a large
lumbriculus.

Two more males cast their shells June 15 and one of them was attacked
by others when only the carapace had been shed and the abdomen was as yet
in its old shell; one-half of the thorax and part of the abdomen were de-
voiired. The other large crayfish was able to flap its abdomen vigorously when
lifted out of the water though its body and chelae were soft and flaccid. Ii>
both cast shell and new one the rostrum was broken off and had evidently not
been regenerated. Still another large male, received in October, 1904, cast its
shell May 19, 1905, and could move about though still soft.

The breeding season of these crayfish was far advanced when they were
received in February. In many cases the males had no sperm left in the defer-
ent ducts and the females had laid their eggs, which in four dead and six live
specimens formed large dark masses attached to the abdominal limbs, or pleo-
pods, and to the sternal hairs of the abdomen. Contrary to expectations, these
eggs were still alive and it was found possible to rear them and to get the sub-
sequent stages in the life history as described below. In the hope of getting
light upon the early part of the breeding season, another lot of thirty-seven
crayfish of the same species were got from the same place October 29, 1904 ; but
here again the beginning of the breeding season had passed. The only two sur-
vivors on arrival were both males, and three others recently dead were also
males, so that here again the vitality of the males seems to exceed that of the
females. In all there were twenty-two males and fifteen females. Five of the
females had eggs upon the pleopods and these were in early cleavage, showing
some twenty nuclei migrating to the surface. It would thus seem that egg-lay-
ing takes place in the autumn, probably in October, and subsequent observations

12 THE YOUNG OF THE CRAYFISHES ASTACUS AND OAMBABUS

%

showed that the eggs are carried by the female all the winter and hatch in the
spring. The eggs on each female were about 500 in number and formed a dark
brown or more usually nearly black mass all over the under side of the abdo-
men. Each egg was very large, about 2.5 mm. in diameter, and as in other
kinds of crayfish, enclosed in a complete capsule of hardened secretions that ex-
tended as a slender stalk to fix each to the setae on the pleopods, or, in some
cases, to the setae on the sternal ridges of the abdomen. All the eggs seemed
in good condition except a cluster of four or five among the brown eggs of
one female and these few were overgrown with a fungus.

The darker eggs plainly showed embryos in the stage represented by
Keichenbach ('86) as J, fig. 12, standing out as a whitish area on one side of
each egg. Thus the embryo had already advanced to a condition in which the
embryonic area occupied a considerable part of one-half of the spherical egg.
There was still a wide margin between the appendages and the well elevated
wall that surrounded all the posterior part of the embryo. The eyes, two pair
of antenna1, mandibles, maxillae, maxillipeds, and five ' periopods were well
marked. The posterior four periopods and the abdomen projected forward
over the thorax so that the abdomen reached to the first maxilla1. The eggs
of one female showed in addition to the above embryo many nuclei scattered
over the nonembryonic areas of the egg and plainly seen against the brown
background of yolk.

In one female the eggs were covered by a dark deposit that had to be
scraped off before the glossy egg capsule and the contained embryo could be
seen.

A few eggs were greenish and covered by a deposit that could be scraped
off; when these were opened, or when boiled, the contained embryo was found
to be in the stage II of Reichenbach.

In one black egg the heart of the embryo was seen to beat very faintly,
and after the eggs had been kept in water twenty-four hours many eggs showed
the heart beating and were kept in the hope that they would develop. In water
about 9° C. the eggs that were still attached to the abdomen of living females
did develop, though very slowly, as will be seen from the following results.

After nine days, March 2, the embryos were perceptibly enlarged with
longer antenna? and abdomen, the second antenna? reaching back nearly half way
to the end of the limb-bearing region. The heart, now lying in a plane at right
angles to the ventral surface and above the base of the abdomen, was beating
so strongly as to give a decided jerk to the thoracic limbs. In one embryo it
beat at the rate of 66 to the minute and in another at 82. Inside the outer egg
capsule there was evidently a delicate inner membrane investing the embryo.

For six days more the only change noted was a slight increase in size and
the extension of the second antennnc beyond the middle of the limb-bearing
region.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS 13

Four days later a marked widening of the anterior part of the embryonic
area had taken place and the slow growth of the abdomen had brought its tip
up to the posterior edge of the mouth. In another week the still larger em-
bryos had antennae reaching nearly to the end of the depressed, limb-bearing,
region and the abdomen reached forward over the mouth as far as the bases of
the second antenna\

Embryos of this age, some twenty- five days after they were received, were
very attractive objects seen through the transparent egg capsules. The trans-
parent limbs stood out strongly contrasted against the dark red yolk mass that
still took up the major part of the spherical egg. On each side of the egg the
boundary of the yolk mass was slightly incised where the "liver" was forming.
When such embryos were plunged a moment into boiling water and then put
into cold water a mere scratch of a needle sufficed to cause the tough outer
capsule to open with explosive force and the embryo was readily removed, leav-
ing even its thin membrane sticking to the inside of the capsule.

During another week there was but little increase in the length of the ap-
pendages, but through the transparent walls of the limbs and body a few blood
corpuscles were seen passing along in the large median thoracic artery and
in the antennae and periopods.

Ten days later, April 5, when the water had risen from 9° to 11°, the size
had markedly increased and the embryo instead of being restricted to a flat
region upon one side of the sphere could no longer be seen from a single point
of view, since it now extended in a curved surface over one-half of the egg. The
long antennae now met one another and their tips overlapped at the deep notch
where the abdomen joined the thorax. The legs and chelae had grown long
enough to overlie the abdomen and to conceal its tip. Such embryos were
nearly in the stage K of Eeichenbach and were prettily colored. The carapace
had bright red pigment along its ventral border, the dark red-brown yolk took
up less than half the bulk of the egg and was divided by a deep fissure into an-
terior and posterior lobes which were encroached upon by the "liver" which
was conspicuously colored. In one its contents were red and in fifteen green-
ish and translucent or else white-yellow and opaque. The large eyes had also
some pigment formed in them.

Eleven days later the elongated walking legs and chelae reached forward
over the posterior edges of the eyes. Pigment cells were as yet not seen in
the above limbs, but were conspicuous in the first and second antennas and in
the abdomen as well as the thorax. The delicate inner membrane was seen
loosely investing the tips of the chelae like a cast-off exoskeleton.

Some six days later the embryo had passed beyond the stage K and was
nearly ready to hatch. The limbs were even longer, so that the chelas reached
over part of the eyes and the antennae overlapped one another the whole width

14 • THE YOUNG OF THE CHAYFISHES ASTACUS AND CAMBAEUS

of the abdomen in such a way that the left passing posterior to the right had
its tip on the right side and the right passing anterior to the left had its tip
on the left side. While all the eggs were still alive and had been kept well
aerated by the swaying movement of the pleopods that the mother makes, seem-
ingly for this purpose, yet some of them showed the effects of such a very long
existence in the water by being covered over upon the outside of the egg cap-
sule with deposits which in some cases were mixed with growths of minute
fungi and in some with vorticellae. The eggs seemed under tension and burst
open when thrown into hot Worcester's liquid; the touch of a needle to the live
egg also caused its capsule to pop open.

As seen under a pocket lens, these eggs nearly ready to hatch present a
most attractive appearance. The carapace is spangled with branching, ver-
milion, pigment cells that are especially numerous along its ventral edges and
near the base of the abdomen, which is broad and also well pigmented witli
the same kind of cell. The antennae and antennules have both red and blue
pigment cells on their basal part, but these cells are not numerous and are
entirely absent from the filaments. The chelae and walking legs have some few
scattered pigment cells. The still large dark red-brown yolk mass has the
forked, light-colored, "liver" projecting into it. The eyes are darkly pig-
mented in all their central parts, while the surface is still clear and transparent
for some distance inward.

The actual hatching of the eggs took place on one female April 25-27, and
on another May 1-6, and was prolonged over several days, that is, not all the
eggs on one female hatched at the same time, but whether this is normal or in-
duced by the artificial conditions remains to be found out from study of these
crayfish in their native waters. These eggs had thus required 62 to 64 days
in one case and 67 to 71 days in the other to develop from the well advanced
embryo of stages H and J of Beichenbach to the hatching larva. The tem-
perature of the water had slowly risen from 9° C. to 14° C.

When a female died before the eggs hatched, it was found possible to
hatch the eggs by cutting off the pleopods of the mother and fastening them
to pieces of floating cork so that the eggs would be suspended in well aerated
water.

In hatching, the egg capsule burst open over the back of the embryo, and
usually opposite to the egg stalk, and then the embryo slowly glided out back-
ward, much in the same way as has been described for Cambarus (Andrews,
'04).

In all crayfish, and in many other Crustacea, the eggs remain firmly
fastened to the mother during the whole period of development and when the
embryo escapes from the egg-shell the old shell remains still fastened by a
strong stalk that is stuck to the maternal setae. In this Astacus as the em-

THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBARUS 15

bryo slowly emerged from the egg capsule it was evidently in a very inactive,
helpless state, soft and unable to use its limbs, so that one might expect it to
drop away from the egg-shell, fall to the ground, and continue its life, if at all,
away from the mother. However, it is well known that young crayfish remain
for some time upon the abdomen of the mother, which they do not leave tilt they
are well able to swim and to walk. This period of interrelation between mother
and offspring deserves special study and we will describe more in detail than
has hitherto been done for any crayfish the remarkable structures used in en-
suring the connection of mother and young from the moment of hatching up to
the time of real independence and free life.

Instead of dropping away entirely from the egg-case, each soft, helpless,
larva hung attached to the inside of the egg-case by a delicate thread which was
firmly fastened at one end to the inside of the egg-case and at the other end to
the telson of the larva. The soft, pink-colored larvae thus at first hung out
from the egg capsules like the pulps from burst grape-skins and were then pre-
vented from entirely falling away from their capsules by these threads, so that
they suggested the seeds of the "cucumber tree" dangling out of their pods.
As the young remained limp and helpless for some time these "telson threads,"
as we may call them, appeared to be of great use, since without them the larvae
would have fallen to the bottom of the water and having lost connection with
the parent have had small chance of survival, lacking the protection or aeration
furnished by the mother.

Such telson threads are doubtless found in the European Astacus, for in
a footnote added by M. Eobin to Chantran's paper ('70), we read: "J'ai pu
constater, a 1'aide du microscope, comme 1'a montre M. Chantran a 1'Acad-
emie, que les petits restent pendus sous 1 'abdomen de la mere, par 1'interme-
daire d'un filament hyal in, chitineux, qui s'etend d'un point de la face interne
de la coque de I'o3uf jusq'aux quartre filaments les plus interns de chacun des
lobes de la lame membraneuse mediane de 1'appendice caudal. Ce filament ex-
iste deja lorsque les embryons n'ont encore attaint que les trois quarts environ
de leur developpement avant 1'eclosion. " And the same general fact is men-
tioned in the report of the committee awarding the Montyon prize to Chantran
(C. K., 75, 1872, p. 1341). Of the above passage Huxley ('80, p. 352) says: "Is
this a larval coat? Rathke does not mention it and I have seen nothing of it
in those recently hatched young which I have had the opportunity of examin-
ing."

The exact mode of attachment of this filament, or telson thread, and its
probable nature will be described below in connection with the "telson of the
larva of this American Astacus and later on in considering the like structure in
Cambarus.

The size of the larva in its first stage is indicated by the following rough

16 THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBARUS

measurements of preserved specimens : Length of head-thorax, 4 mm. ; width,
3 mm. ; depth, 3 mm. Length of abdomen, 5 mm. Length of antenna, 6 mm.
Length of chela, 5 mm.

Eeturning to the account of the hatching young, it is to be noted that the
activities of the young were but slowly acquired; here and there amongst the
mass of eggs and young upon the female some larvae showed feeble movements
of the scaphognathites and, later, rhythmic respiratory movements ; the long
antennas projecting into the water moved somewhat, the legs and chelae some-
times moved and the claws opened and shut. Upon escaping from the spherical
egg-case the larva became but little straightened out and remained essentially a
spheroidal head-thorax with a weak abdomen bent in under it and with soft,
pendent limbs. However, in from one to six hours the limbs reaching about,
the claws opening and shutting and the abdomen sometimes flapping up and
down, it was seen that the chelae managed to get hold of the stalk of the egg-
case. Henceforth the larvae held fast by the chelae though for a time still
fastened by the telson thread also.

The pleopods of the parent were now covered over with a mass of flesh-
colored young, showing slight movements and conspicuously marked by the
two-lobed, red yolk mass, by the dark eyes and by the yellowish "liver" areas.
The dark yolk masses showing through the pale bodies gave somewhat the gen-
eral appearance represented in figure 2, which was made from a photograph
of a living female shortly after the eggs (excepting one) had hatched.

When forcibly torn loose from the mother the recently hatched larvae, too
spheroidal to rest on their ventral side and unable to stand on their legs, lay
for two days on their sides, kicking their legs but unable to walk; when, how-
ever, much disturbed, they managed to swim forward along the bottom of the
dish by flapping their abdomens, though they still remained on their sides.
When offered a piece of rough string, such young seized it and remained sus-
pended in the water, holding fast by their chelae. In this way some larvae were
kept suspended in running water and successfully carried into later larval
stages away from association with the mother.

This tending to seize hold with the chelae is accompanied by a tendency to
push far in amongst the general mass of young attached to the pleopods, so
that in a few days all the young are densely crowded together in a compact
mass and their long chelae are seen to reach far in and to be fastened either
to the stalks of egg-cases or to the coagulum that binds the setae together on
the pleopods. Generally both chelae grasped the same egg stalk but not always
and one larva was seen holding by one chelae to an egg stalk on one pleopod
and by the other chelae to an egg stalk upon the next pleapod. As the rhyth-
mic movements of the pleopods continued after the young were hatched,
this larva was in danger of having its chelae stretched apart.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 17

The fixation of the chelae was a gradual process ; at first the claws of the
chelae were not opened even when those of the walking legs were opened and
shut, but soon the chelae claws opened and shut and soon seized hold of any
solid object accessible. Sometimes the object seized was again let loose but be-
fore long the chela? had reached in among the mass of young and eggs far-
enough to find and fix upon one of the egg stalks, which are of a material and
size seemingly well fitted for the attachment of. the claws. Henceforth the chela?
seemed to remain always fast and their structure as described below indicates
that once imbedded in the material of the egg stalk the tips of the claws could
scarcely be liberated by the crayfish. This fixation was first made out in the
English crayfish by Huxley ('80), who inferred that when once fast it would
be difficult, or impossible, for the claws to open again.

This use of the chelae to obtain attachment to the mother was exercised
with what appeared to be very earnest effort and once successful it was found
that the telson thread was soon ruptured. And then if the larva? were dis-
turbed they flapped their abdomens up and down and it was seen that the tel-
son thread had broken so that a piece of it was still attached to the telson and
was waved about by the telson like a bit of rag fastened to it. Henceforth the
young held fast by the chelae only.

The general appearance of this mass of young on the mother was peculiar
since the rounded head-thorax was the chief part visible in each and this was
of light color with a striking bilobed or horseshoe-shaped, dark red, yolk mass
across it. The legs and abdomen were concealed and the dark eyes were gen-
erally out of view. With bent heads and outstretched limbs their attitude
ludicrously suggested one of supplication.

Thus they remained for some days. When disturbed the young made tramp-
ing movements with their legs but did not move from the place to which they
were fixed by their long chela?. The abdomen, carried down under the thorax
somewhat as in the embryo, was not readily moved but with sufficient stimulus
from a needle point was flapped rapidly back and forth. When a larva was
forcibly pulled off from the mass its chela?, still attached, were stretched out to
their fullest extent and when the larva was released the chelae contracted and
made the larva spring back into place where its limbs and abdomen were again
drawn in under the thorax and the creature became again one of the herd of
"bison" presenting only their humped backs to the observer.' If by stronger
pulling the larvae were torn loose from the mother the chela? parted from the
egg stalks without breaking and reaching about seized hold of adjacent objects
such as the antennae of other larvae. Left to themselves on the mass, these
separated larvae soon got back again amongst the crowd ; but if put upon the
bottom of the dish they did not yet stand up but only gyrated about by flap-
ping their abdomens.

18 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

The long antennae remained for the most part low down amongst the gen-
eral mass and did not yet project up above the level of the rounded backs ;
they were, however, carried out in front and not, as in Cambarus affinis, tucked
in between the legs.

Fastened thus to the mother, the larva1 remained some days and then cast-
ing off their shells passed into a second larval stage which also lived upon the
mother. In one female kept in running water at 17° C., the duration of the first
larval stage was only four days, but some young of another female which
were kept suspended from strings hanging in water in a warm room remained
five to seven days before changing to the second stage and their fellows kept
in water at 14° C. remained eleven to thirteen days in the first stage. Dur-
ing this long existence in the first larval stage the only change noted was a slight
darkening of the color which, owing to the scattering of bright red, branching,
pigment cells on a white background appeared to the naked eye flesh-color.

Before considering the transition from the first to the second stages we will
describe the details of the external form and appendages of the first larva.

A side view of the living larva (fig. 3), suggests embryonic incompleteness
in that the antenna', abdomen, and limbs are carried downward in n way not
adapted to locomotion, while the globose cephalothorax and large eyes with short
stalks are features of an embryo rather than of an active larva. The dark mass
seen in the figure was the still conspicuous red yolk mass which from the dorsal
view (fig. 4), was balanced right and left in the anterior half of the cephalo-
thorax. In life the larva was translucent yet brilliantly colored by the scat-
tered pigment cells indicated in black in the figures and which were absent only
from the terminal filaments of the antennas and from most of the segments of
the legs. In the side view the first and second antennae are conspicuous, the
three maxillipeds are seen in part, the chelae are very long and heavy and the
four walking legs are long and weak. The abdomen bears only four pairs of
pleopods and these are small, weak, and bifid. The first and sixth pleopods are
not seen and the abdomen ends in a simple telson in place of the locomotor fan
of the later larvae and adults. The larva is evidently very defective in locomotor
apparatus, has its sensory organs not perfected, and is specialized in its strong
clinging organs, the chelae, and in its large digestive apparatus for utilization
of the stored-up yolk. It is still essentially embryo-like in structure and in
mode of dependent life, but is exposed free to the water.

The same general features are shown in the dorsal view (fig. 4), which
shows the split-open egg capsule and its stalk, connected by a slender thread
to the telson of the larva, a "telson- thread" that is fast at one end to the
peculiar fan-like telson of the larva and at the other end to the inside of the
ruptured egg capsule. It will be noted that the head-thorax though globoidal is
considerably elongated and does not have the swollen sides shown in Huxley's

THE YOUNG OF THE CBAYFISHES ASTACUS AND CAMBABUS 19

figures of the English Astacus, which, however, were doubtless drawn from
alcoholic specimens, and in A leniusculus the action of alcohol is to cause great
distortion of the branchiostegites. As compared with the adult, however, the
proportions of the head-thorax are embryonic and there must needs be much
greater elongation as well as lateral and vertical changes to bring about adult
proportions.

While both from side and top views (figs. 3 and 4), the characteristic
rostral spine of such Crustacea seems absent, full front and diagonal side
views (fig. 5) show the rostrum to be well developed and armed with lateral
spines, but so bent down between the eyes as to be of no such use as a de-
fense as it later will be in active stages of the larva. The habit of the first
stage which clings to the parent is thus correlated with imperfections of defen-
sive armament as well as with presence of food yolk and imperfections of loco-
motor organs. Among the latter characters may be reckoned the smooth sur-
faces of the limbs and absence of setae that later will increase the areas of
resistance for striking against the water as well as furnish means of sense
perception. The lack of setae represented in figures 3 and 4 is still more strik-
ing in enlarged views of the limbs and is in strong contrast to the hirsute char-
acter of all parts of the active larvae and of the adults, and this absence of
setae gives the larva? a decidedly embryonic appearance.

The pronounced incompleteness of locomotor organs is also associated with
the shortness of the thoracic region bearing legs; thus the chelae arise farther
from the anterior than from the posterior ends of the head-thorax and leave
little space for the walking legs, while the anterior region containing the yelk is
greatly developed in size.

Next taking up in sequence the nineteen pairs of appendages of the adult
we find them represented in the first larva by seventeen pairs that have in the
gross, as made out by Eathke for embryos about to hatch, the essential mor-
phology of the adult appendages but lack the setae and differ in proportion as
will be seen from the following account and illustrations.

The whole exterior of the larva in its first stage is covered by a chitinous
exoskeleton of such resistance that when the young were thrown into Wor-
cester's liquid they did not die for several minutes; the appendages were cut
off separately from such hardened embryos and gave the views represented in
the following illustrations.

The first antenna stands out horizontally in front of the head (figs. 3, 4)
and is straight; as seen in figure 6, it has three basal segments, five in exopo-
dite and in endopodite. The segmentation of the endopodite is very obscure.
The terminal segment in both endopodite and exopodite bears three obscurely
pointed spines, one of which, in the exopodite, is long and apparently of the
same character as the sensory seta? found there in later stages. On the long

20 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

basal and next segment of the protopodite there are a few blunt spines as in-
dicated in figure 6. This also shows the auditory organ as an open pit on the
upper surface of the basal segment, in the part that is swollen out laterally.

The second antenna (fig. 7), though it has a long filament, is still embryonic
in proportions. The base consists of two short segments, the first of which
bears the very large prominence that faces inward and has the opening of
the green gland, or kidney, within its depressed top. The second segment
bears a few blunt distal spines of large size. The exopodite is a very large
flat scale ending in a blunt point and bearing some sixteen blunt spines along
its serrated inner and anterior edges. The endopodite consists of three large
basal segments and of a long round filament of many segments, forty-five to
fifty, the first of which is long and slender, while the following ones are each
about one-third as long as the first. The terminal segments are again more long
and slender. As indicated in figure 7, there are a few spines at the distal edges
of some of the terminal segments and of some of the others near the tip. In
the adult there may be 125 segments.

The mandibles (fig. 8) have a well developed cutting edge which, however, is
smooth and not toothed as it is in all later, functional, stages and there was
no evidence found that these organs were used. The palpus has three segments
and is smooth except for the distal face of the third segment which is sparsely
set with rather acute spines, many of which are shown in figure 8, and more
of which are present upon the inner aspect and not seen from this point of
view. The palp is thus a blunt club with terminal spines.

The first maxilla (fig. 9) is very small and made of two flat plates and a
somewhat rounded and blunt endopodite of curved finger-shape. Here for the
first time we meet with a few small, plumose seta; along the outer edge of the
distal segment. The two flat plates that represent the protopodite are spinulous
at the ends, much as in the palp of the mandible. The distal piece is also armed
with a row of a few spines along its proximal edge as seen in figure 9. The
ends of both plates are set with spines on the face toward the mouth; the
proximal plate is rounded, the distal one truncated to form a jaw-like organ.

The second maxilla (fig. 10) bears the long scaphognathite which has a
dense row of plumose setae all along its extensive free edges. There are also
a few plumose setae at the base of the endopodite, as in the first maxilla (fig.
9). As above noted one of the first muscular activities acquired after hatching
is the slowly developed rhythmic beat of the scaphognathite, and with this use
of this appendage there is present an armament of plumose setae lacking else-
where in the locomotor organs of the larva. While these plumose setae are not
used in locomotion their function as flexible areas of resistance to the water
which the scaphognathite bales out of the branchial chamber is akin to that of
locomotor setae. The rest of the second maxilla is nearly bare of setae, but there

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 21

are a few, long hair-like setae standing out from the external face of the pro-
topodite. The protopodite has the sanoe two plates seen in the first maxilla
(fig. 9), but each is deeply cleft, so that four free tips project toward the
mouth. The four tips each bear blunt spines on the outer and distal faces as
shown in figure 10, while upon the inner faces toward the mouth they are all set
with longer, sharp, curved spines that are claw-like. The endopodite though
longer arid more slender than in the firstmaxilla is still very simple and not seg-
mented.

The first maxilliped (fig. 11) shows the protopodite again reduced to two
flat plates much as in the first maxilla (fig. 9), and there are simple spinules
on their cutting edges. The endopodite is small and simple, intermediate be-
tween that of the second and first maxillae. In place of the scaphognathite
there are two movable parts ; a long flat plate, the epipodite, which is without
seta; though sparsely spinulous on its posterior edge; and a very long and
prominent e'xopodite. The exopodite has a very long swollen basal part with
very long plumose setas on its outer edge as shown in figure 11 and is else-
where naked. The terminal part is long, slender and with a very few spines
at its tip. As the base of the exopodite lies over the distal end of the epipodite
it is not readily seen that the epipodite has a short truncated extension sug-
gesting the anterior end of the scaphognathite as well as the evident posterior
blade that reached back into the gill chamber and is comparable to the like
portion of the scaphognathite.

The second maxilla (fig. 12) is more complex; the two segments of the pro-
topodite are subordinate in mass and extent to the greatly developed en-
dopodite and gill structures, but they bear a few plumose setae upon their
inner edges. The endopodite resembles that of the first maxilla in position,
general form and curvature, but is not only larger but subdivided into five seg-
ments and bears spines. In addition to the spines shown in figure 12, there are
also long curved ones on the inner face of the terminal segment. Compared
with that of the first maxilliped, the exopodite of the second has a very narrow
basal part which is without plumose set;c but bears a few long spines on its
external edge. The epipodite is present as a long, curved lamina, bilobed at the
tip, and along its inner face are borne the numerous blunt filaments of the gill,
podobranch. This podobranch is free at its tip, but elsewhere adnate to the
lamina and bearing two rows of blunt side papillae or gill filaments which are
directed toward the apex, and increase in size in each row from base to apex.
The epipodite lamina has a few plumose setne on the rounded ridge at its base
and along its edges are scattered curved, short hooks, while its emarginate tip
bears a few blunt, fringe-like papillae. In addition to the above gill there is one
arthrobranch that is shown in figure 12 to have a long slender stem ending
bluntly and bearing two rows of blunt, curved, finger-like lateral filaments

22 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

which may each end with a small, blunt spine. The third maxilliped (fig. 13)
exhibits the typical morphology of this organ in the adult; a somewhat two
jointed basal protopodite bears a large five-jointed endopodite of great size,
a long slender exopodite, a large epipodite and podobranch; and two arthro-
branchi.e arise from the region connecting the appendage to the body.

The endopodite bears spines upon all its segments and the protopodite has
a couple of small spines upon its distal segment and a plumose setae upon its
proximal .segment. The exopodite, in contrast to that of the second maxilliped,
has a shorter and more slender basal segment devoid of spines, while the
second segment has several spines at and near its tip. The lamina .of the
epipodite has the same characters as in the second maxilliped, but the plumose
set* along its basal ridge are twice as many. The podobranch is like that of
the second maxilliped. Of the two arthrobranchiae the anterior one is much
like its homologue on the second maxilliped, while the posterior one, nearer the
observer in figure 13, is smaller and more simple with fewer lateral filaments.

Coming next to the ambulatory appendages, we find the usual large chela?,
the two pairs of slender chelate and two pairs of non-chelate legs (figs. 14, 15,
16, 17, 18). In these appendages of the first larva there are, as in the adults,
no exopodites, and even the remarkable exopodite setae of later larvas and of
adults are absent in this first stage, thus adding to the simplicity of the limbs,
which is also expressed in the entire absence of plumose sets and the presence
of but few sharp spines.

The chela (fig. 14) has the recurved terminal hooks first made out by Hux-
ley in the English Astacus, and which lead to the firm locking of the chelae to
the egg stalk, as above narrated; and the opposing edges of the claw are ser-
rated from the presence of sharp spines pointing toward its tip. The chela
bears very large sharp protuberances along the inner edge of .the meropodite
segment, of no apparent use, while the great length and thickness of the whole
limb is apparently necessary in that firm holding of the larva to the mother
which resists the force of the maternal pleopods that swing the larvae back and
forth.

The epipodite and gills of the chela; are like those of the third maxilliped.
The following two legs (figs. 15, 16) are like one another in every way
except in proportion, the first being shorter than the second. Each has a
sharp claw with spines pointing toward the tip, but the tips are not recurved
as is the case in the big chelae. The gills on these two appendages are like those
of the chela, but there is in addition a slender simple gill upon the body wall
near the arthrobranchiae. This pleurobranchia is a single filament with no
lateral outgrowths and may be regarded as rudimentary at this stage, as it is
also in the adult.

The remaining legs (figs. 1.7, 18) have terminal segments almost like those

THE YUUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

23

of the preceding legs, but there being no opposing outgrowth of the propodite,
there is no claw. The legs increase in length and in slenderness from before
back in the series behind the chelae. The penultimate leg (fig. 17) has a longer
pleurobranch associated with it but otherwise its gills are as in the preceding
limb. The last leg, however (fig. 18), has its gills suddenly reduced; in place of
the epipodite and podobranch there are but a few plumose hairs such as stand
upon the basal ridge of the epipodite of the preceding somites. The arthro-
branchs are entirely absent and there is but one gill which is a pleurobranch,
which, however, in place of being a simple filament or rudiment, resembles a re-
duced or simple arthrobranch in that it has about seven short lateral processes
in two imperfect rows.

The branchial formula of the first larval stage of Astacus leniusculus is
then as is given in the table below. This was found to be just the same in the
adult of this species and it is said to be the same in the English Astacus pal-
lipcs, except that the latter lacks the rudimentary pleurobranch on the somite
of the first leg.

Podo-
brancliise.

Arthrobranchise.

Pleuro-
branchise.

Total.

Anterior.

Posterior.

Somite of 2d maxilliped

1
1
1
1
1
1
0

1
1
1

1
1
1
0

0
1
1
1
1
1
0

0
0
0
1 R
1R
1 R
1

2
3
3
3+lR
3-f 1 R
3 + 1 R
1

Somite of 3d maxilliped
Somite of chela
Somite of 1st leg
Somite of 2d leg

Somite of 3d leg

Somite of 4th leg

6

6

5

1 +311

18 + 3R

The above illustrations of the separate appendages of the head-thorax are
the first ones as yet given of any larval Astacus, since the previous illustra-
tions of European forms are only the small maxillae and maxilliped of an em-
bryo not yet hatched as depicted by Eathke ('29, fig. 29), the tip of the chela
shown by Huxley ('80, fig. 8), and the under side of the abdomen with its
pleopods figured by Eeichenbach ('86).

Upon comparing the adult appendages of Astacus leniusculus with those
of first larva as above described, the fundamental agreement in morphology
was obvious, but there were the following differences which all suggest a linger-
ing on of embryonic characters into the life outside the egg-shell. Throughout
all the appendages there was a marked lack of setae correlated with evident lack
of locomotion and probable weakness of sensory activity. Excepting the chela>
the cephalothoracic appendages had no obvious use. The first antenna, having

24 THK YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

but five segments in its exopodite and in its endopodite, is but embryonic com-
pared with the adult that has at least thirty-five in its exopodite and almost as
many in its endopodite, a difference which is of great moment when we con-
sider the repetition of special sense organs that are found on many successive
segments of the exopodite of the adult. The auditory organ also is apparently
of no functional value in the early larva. The number of segments in the fila-
ment of the second antenna must also increase greatly to form the one hun-
dred and twenty-five of the adult; an increase apparently brought about by in-
terpolating new segments at various places by division of the old ones into
two.

While all the adult appendages of the head-thorax are represented in the
larva at hatching, this is not the case for the abdomen, for the sixth pair of ab-
dominal appendages are not externally present and the first pair which in the
adult male are so essential are absent in the first larva as they also are in the
adult female. The other abdominal appendages are four pairs of simple ple-
opods which hang down beyond the pleural plates of the abdomen so that they
are seen from a side view (fig. 3). Each pleopod (fig. 39) is as in the adult
composed of a short and a long segment that make up the protopodite and of
two simple terminal plates, the endopodite and the exopodite. These are
slightly curved and armed at the ends and to some extent on the edges with
small weak spines and they entirely lack the plumose setae that makes them use-
ful in the adult for fanning the water. The illustration is of the anterior face
of the left pleopod of the second abdominal segment and shows that the ex-
opodite is longer and wider than the endopodite, while in the adult the exopodite
is much the shorter and smaller in the female pleopods that bear the eggs and
in the male pleopods that transfer sperm. The appendages of the sixth somite
though not externally free are yet present and of large size though imperfect
in development and lie within the s-ubstance of the telson, as can be seen in
transparent living larvae. It is their presence which swells out this region
ventrally and gives rise to the protuberance seen from the side view (fig. 3).
Looking at the telson from above (fig. 20), the very imperfect future sixth ple-
opods are seen as two somewhat less translucent areas, right and left in the
anterior part of the telson and each having an outline suggesting that of a mit-
ten. Only later will these concealed buds of the sixth appendages burst out
after a moulting and expand as the very large lateral parts of the caudal fan,
so essential in quick locomotion. This retention of these appendages within
the telson in Astacus was known to Huxley ('80), and figured by Eeichenbach
('86).

The telson requires special consideration in connection with the "telson-
thread," as mentioned above. The telson itself is a very large plate with
nearly circular outline and is thin posterior to the above region occupied by

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAEUS 25

the buds of the pleopods on either side of the intestine and anus. In structure
it is essentially a translucent, vascular, connective tissue mass over which are
scattered brilliant vermilion pigment cells, indicated in black in figure 20, and
which is covered by a thin epidermis and thin chitinous cuticle. Along most of
the free margin of the telson is a row of blunt, stiff papillse, or spines. In all
there are about sixty-six of these spines arranged symmetrically, half on each
side of the median plane. In the figure of Astacus given by Eeichenbach ('86)
there are but twenty-five spines or dentations on each side of the median line
and this may well be a character of systematic value. In addition to the
thirty-three lateral spines of Astacus leniusculus there were six or seven
smaller, blunt spines on each side which stand in between some of the larger
ones, one small one between two larger ones, and generally not so near the edge
but more up on the dorsal surface of the telson.

The interior of the telson has a radiated appearance like that figured by
Bemak and by Eeichenbach and which was referred by Huxley to the disposi-
tion of vascular canals; but in our present larvae this radiation is due to long
delicate lines passing centrally inward, one from each lateral spine and from
some of the smaller spines, thus making the divergent system radiating from
near the anal region as shown in figure 20. Subsequent events show that these
lines are the forming plumose setse for the perfect locomotor telson of later
larval stages. Each when enlarged (figs. 21, 22) is a bundle of fibrillae that are
very small in comparison with the nuclei of the epidermis as each bundle of very
many fibrils is but once or twice the diameter of a nucleus. These radiating
lines are in fact to be likened to compressed bottle brushes which later will
expand as the perfect locomotor plumes on the telson of the second larval stage
(fig. 23). The plumes are being made within epidermal tubes or glands and
between the successive radiating glands the vascular spaces, also radiating,
form the justification for Huxley's interpretation.

During the first hours of larval life the telson is connected to the inside of
the egg case by the long telson thread represented in figure 4. This is a trans-
lucent, chi tin-like membrane, or flat ribbon, showing a striated appearance due
to fine wrinkles in it (fig. 20), but otherwise apparently homogeneous. Though
seemingly but superficially attached to the telson the contact is a very firm one
so that when the larva succeeds in getting hold of the egg stalk and finally
flaps its abdomen strongly enough the telson thread is broken before it is torn
loose from the telson. When enlarged (fig. 21) the mode of attachment of the
very thin but tough membrance is seen to be, that ten of the marginal spines of
the telson bear special hook-like projections that are fast to the membrane.
These few spines are different from the others though some of the adjacent
ones have somewhat of the same structure at their tips. While in figure 21 the
spines and their processes are represented in black, they are in nature trans-

8

26 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS

parent, colorless and very inconspicuous, especially the processes which are
hyalin, myelin-like protrusions, suggesting the products of glandular activity.
While many of these protrusions end bluntly others seem to be continued as
fine threads that are fast to the membrane or telson thread. Moreover, many
of the protrusions bridge over the space from one spine to the next and are con-
tinuous with adjacent protrusions as if they had flowed out when viscid and then
coagulated. Such bridges make adjacent spines into' hooks that hold fast to
the membrane, but the ultimate and essential fastening of the membrane to the
telson is by fine threads of some coagulated material that seems to be a con-
tinuation of the grosser protrusions figured in black in figure 21.

It would appear from the statement of M. Eobin cited above (page 15)
that in the Astacus studied by Chantran there are but eight spines used for
attachment to the telson thread.

The origin of these peculiar glandular spines, for such they seem to be,
is to be sought in the embryo. At the time of hatching the egg capsule breaks
and for a brief period the embryo may still be enveloped in a very delicate
membrane which passes over the abdomen and all about the telson. At that
period the spines of the terminal part of the telson abut against the invest-
ing membrane as shown in figure 22, which is from a specimen just hatch-
ing and killed in Pereny's liquor. Here are shown the epidermal nuclei, the
striations, or forming plumes of the future telson, continuing up through the
body of the spines, only three of which are drawn ; and at the tips of the spines
fountain-like masses of blunt protrusions, swollen at the tip and in many cases
pressed against the membrane. It would seem that a viscid mass had been
poured out from the tips of the spines and that this oozing out in threads had
become firmly soldered to the membrane.

As far as made out the origin of the supporting telson thread is thus as
follows. The thread is really a membrane and when the embryo is hatching
this membrane is spread like a loose skin all over the embryo inside of the
egg case. When the embryo hatches it also sheds this membrane, coming
finally to pull its abdomen out of the part of the membrane that surrounds
the abdomen like a long bag. The bottom of the bag is, however, fastened to
the tip of the telson as indicated in figure 22, so that the creature cannot get
entirely free from the bag but pulling out its abdomen pulls up the bottom of
the bag and turns the bag inside out. The struggles of the larva drag the
membrane into a long thread, and one end of this remains attached to the tel-
son spines as seen in figure 21. Once this is accomplished the fact that the
clear thread is really a cast-off membrane would not be suspected, since it
seems a homogeneous, finely wrinkled thread that might well be a secretion.

The similar structure in the European Astacus was mentioned merely as
a filament as cited above, page 15, but Huxley intuitively queried if it might
be a larval skin.

THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBARUS 27

The other end of the telson thread remained fast inside the egg capsule
(fig. 4), and this attachment is as important as the above described attach-
ment to the telson in making the thread of use to secure the larva from being
lost. How the connection of the inner membrane to the egg capsule was
brought about was not determined but it was existent long before the embryo
hatched. Embryos three days before hatching killed in Worcester's liquid and
soaked a week in five per' cent potash showed an outer egg capsule, an inner shell
and a membrane that was loose and visible over the chelae and over the deeply
bifid telson which already bore terminal spines. And embryos nine days be-
fore hatching showed the same double shell and membrane, but no telson spines.

The telson thread is thus a thin membrane formed about the embryo and
early fastened by radiating fibrils (fig. 4) to the inside of the inner of the two
layers of the egg capsule. Later in the life of the embryo this membrane be-
comes also fastened to the telson by secretory activity of the terminal spines.
When the embryo hatches the membrane is ruptured and in part turned inside
out and drawn into a thread-like form, fastened at both ends. Other facts re-
garding the telson thread will be given below in the description of Cambarus,
in which it also exists.

The passage from the first to the second larval stages was seen in some
larvae lying in the Bottom of a dish, and in others that had fixed themselves to
strings. In these the old larval skin burst open and the second larva, as it
were, "oozed" out backward for several minutes and its chelae and abdomen re-
mained longer inside the old skin but were then suddenly withdrawn. For a few
minutes the larva in its new stage lay stretched out straight, as if dead but then
flopped its abdomen, moved its legs, got upright and walked and even swam
backward and finally crawled up into the piles of other young in the same
second stage.

While the larva in the first stage was inactive and remained always
fastened to the mother, the second larva was active and finally abandoned the
mother though for a time still associated with her. Upon casting off their first
larval skins the larvae in the second stage leave those skins fastened by their
chelae to the egg stalks on the mother's pleopods, and are free to crawl about
over the pleopods of the mother amongst their numerous fellow-larvae. Soon
these larvae descend the pleopods and make short excursions under the abdo-
men of the resting mother and over various parts of the mother's body, finally
wandering off over the bottom of the aquarium for short distances to return
frequently to the mother again.

The mother thus had fastened to her pleopods a large mass of old egg stalks
and capsules to which were fastened the cast-off skins of the larva?, and over
this mass crawled the active larvae till after a few days the egg cases and cast
skins as well as egg stalks were found to have disappeared leaving the pie-

28 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

opods clean but still occupied by the larvae. In the Astacus in France Chan-
tran ('71) finally convinced himself that the larvae ate their cast skins and the
egg capsules ; and the same probably occurs in Astacus leniusculus.

The habits of the second larvae showed much greater diversity than was
possible in the attached larvae in the first stage but through the early part of
the second stage a tendency to climb seemed a dominant feature of their lives.
When a number were put into a dish by themselves they tended to climb up onto
one another to form a mass but if put back with the mother they soon climbed
up onto her pleopods where they held on so firmly that when a pleopod was cut
off and thrown into 70 per cent alcohol, some of the larvae still retained their
hold though most of them did not. When the larvae alone were in a dish with
a spray of myriophyllum they climbed up it and crawled together in a mass
between the plant and the glass; but they did not climb up onto a piece of
cotton cloth hanging down in the water from a floating cork. Even when the
mother was dead, the young twenty hours after passing into the second stage
continued to hold firmly to the maternal pleopods. But after three more days
the young had ceased to huddle together so much, and crawling about over the
bottom of the aquarium, and sometimes swimming, they were at times carried
away with the current of water. Though some of the larvae concealed them-
selves under ooze and dead leaves at this time, others continued to hold on to
the abdomen of the dead mother for four or five days, when the abdomen was
cut off and fastened at the surface of running water, but about May 18 these
larvae also dropped to the bottom and lived there. This climbing instinct can
then be satisfied in various ways, and when thirteen larvae were removed and
put into a dish with another female bearing young, but few minutes sufficed
for five of the thirteen to find and to climb up onto the pleopods of the strange
female. The possibility of resolving these habits of the young second stage
crayfish into so-called tactic phenomena, into chiefly geotactic and stereotropic
responses, will be considered in connection with some observations upon the
young of Cambarus.

The general form of the second stage as represented in figures 23 and 24
is obviously more like the adult than like the first stage as is true also of the
habit. Comparing these figures with 3 and 4 there is a noteworthy change in
size; after casting off the first skin the crayfish measured 11 mm. from tip of
rostrum to end of telson, exclusive of the long fringe of plumose setae which
made the length 12 mm. if the setae were included, and so greatly enlarged the
area of telson available for locomotion. The thorax was 2 mm. wide and about
2.5 mm. deep. The cephalothorax was 6 mm. and the abdomen 5 mm. long;
the telson was 2 mm. wide without the seta?, and 4 mm. with the setae. The an-
tennae were 10 mm. and the chelae 8 mm. long. All these measurements were
taken from preserved material and show that the animal was now a large larva.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 29

Its brilliant color added to its size made it an attractive larva resembling
a young lobster after the swimming stages. As indicated in black in the above
figures the pigment cells were scattered over the head thorax and abdomen and
more sparingly over the chelae, walking legs and basal parts of the antennae. To
the naked eye the larva walking on the bottom of a dish seems light flesh-color,
translucent and inconspicuous, but the chelae look red, the eyes are dark and
the yolk is still a very evident dark, red-black mass of bilobed form across the
middle of the head thorax. The liver lobes anterior and posterior to the yolk-
were noticeably yellowish and greenish. The abdomen was flesh colored for the
most part, but the telson was nearly colorless and with a fringe of white, clear
setae so long as to suggest a peacock's tail. On the first abdominal somite the
densely crowded pigment formed a conspicuous cross-band (fig. 23). Another
such aggregation of pigment was found posterior to the eye and external to
the base of the rostrum. In addition to the color due to the much branched
red pigment cells, indicated in black in figures 23 and 24, there soon
came to be a variable amount of blue color not so readily seen and due to large
blue pigment cells. In strong light the red pigment often stood forward on a back-
ground of blue. The blue was evident on the basal part of the antenna and
antennule, on the mandible and its palp, but not on the maxillipeds. On the
dorsal side of both thorax and abdomen there were some blue, faint, scattered
areas internal to the red.

As shown in figures 23 and 24, the cephalothorax in passing from the first
to the second stage had become long, narrow, and angular with a long gothic
rostrum standing straight out in front between the eyes on a level with the
back. The rostrum also had large lateral spines at its base and half way out
its length.

In walking about these larvae carried the antennae and the red chelae for-
ward and the abdomen straight out behind as in figure 23, and not bent in
under the thorax as in the first stage. However, when not walking the abdo-
men was bent as in figure 24. As in a young lobster the slow walking was
quickly replaced, at alarm, by rapid backward swimming caused by flapping the
abdomen with its extensive telson fan. As the larvae went about more and more
away from the parent, they became more individual and more complex in their
movements; they were seen to scrape the backs of their heads with their legs,
to raise their chelae as if in defense when a shadow passed over them, and in
other ways to act like an adult crayfish much more than did the sluggish and
simple first larvae.

In watching one of these second larvae slowly walking, the movements of
the five long limbs seemed to be as follows. The fifth, fourth, and third limbs
standing out at the sides of the body (fig. 23), were so bent as to hold the
body high up above the bottom of the dish and swing back and forth as the

30 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAEUS

chief locomotor organs. The chelae were held in readiness in front of the animal
and the second limbs (fig. 23) were bent inward under the body with the tip for-
ward so that in moving forward the body rode over these appendages as upon
levers with very little movement of the base of these appendages. The third
appendages always pointing forward swung from an angle of about 45° with
the side of the body to one of about 70°. The fourth limbs had a very long
swing from a forward position about 45° with the side of the body back past
90° with the side of the body. The fifth limbs had a very short, hobbled,
movement like the third but always directed backward, from about 100° to
120° with the side of the body.

In taking up the appendages of the second larva, in sequence (figs. 25 to
39) it will be noticed that the relative nakedness of the first larva has given
place to a hirsute condition, indicated in figures 23 and 24 ; setae occur upon the
antennae, chela?, legs, pleopods as well as the sides of the abdomen and, as the
separate sketches show, upon all the other appendages. The active second
larva has thus come into possession of sensory and locomotor setae lacking in
the imperfect first stage, and similar to those of the adult stages.

The first antenna (fig. 25) still has the same general form as in the
first stage (fig. 6), it has five segments in exopodite and in endopodite but it is
noticeably more finished in being well armed with setae. The narrow part of
the proximal segment bears a sharp spine upon its inner side. The auditory
pit on the basal segment is now well guarded by a row of plumose setae pass-
ing from the outer edge inward and spread across the orifice of the pit. There
is also a row of sparsely branched plumes along this upper face of this segment
and parallel to its inner edge and in addition there are a few other setae ar-
ranged as in figure 25. The second and the third segments bear long plumose
setae on their inner sides and long, stiff spine-like setae on the external sides of
their distal ends. The endopodite a-nd the exopodite each bear a few long stiff
spine-like setae at the distal ends of their five segments and in addition the char-
acteristic blunt sense clubs of this appendage are now evident. These organs
are placed in groups upon the inner and lower faces of the third, fourth, and
fifth segments of the exopodite. The third segment has a cluster of three upon
its distal edge, the fourth has a group of two at its distal edge while the fifth
has a group of three at its middle part, where its diameter suddenly diminishes.
As all these sensory clubs face downward they are foreshortened in the above
figure and in reality are much longer than shown.

The second antenna (fig. 26) has increased greatly in length over its former
state (fig. 7). Its basal parts are more angular and the excretory cone on the
basal segment is relatively very much smaller while the spines of the second
segment are borne upon a large, scale-like protuberance. The exopodite scale
bears a row of long, plumose setae all along its outer edge while in the first

THE YOUNG OF THE OBAYFISHES ASTACUS AND CAMBARUS 31

stage there were only simple spines to anticipate some of these plumes. The
three large segments of the exopodite are more angular than before and now
bear a few setae while the filament has some fifty-four segments of the form
and proportions shown in figure 26. As these bear needle-like setae on their dis-
tal edges the filament seems under a low magnification somewhat like a brush.

The mandible is not only greatly enlarged but more complex in having an
effective cutting edge no longer smooth but serrated by seven unequal angular
projections (fig. 27). The palp is more complex in having more numerous long,
acicular setae both on the exterior and interior faces of its terminal segment
and a very few sparsely-branched plumes on the distal part of its second seg-
ment. When folded down the palp fits into a deep depression on the inner
face of the mandible (fig. 28), and the proximal border of this depression is
irregularly dentated with rounded protuberances. The exoskeleton over these
dentations and over the sharp teeth of the cutting edge is now very thick and
horny, being solid as far back as the second line in figure 28. While the
acicular setae over the terminal segment of the palp appear smooth under Zeiss
2 A, they are really set with short, fine, side branches along their distal halves
as seen with 2 D, and they have rather bhint points so that they woiild seem to
aid in a brush-like use of the palp.

The first maxilla (fig. 29) has progressed beyond its former stage (fig. 9),
chiefly in the outgrowth of long setae in place of blunt spines and also in the
addition of setae where there were no outgrowths at all. The setae are of two
kinds, a few plumose and many acicular ; the latter are found chiefly on the ends
of the two plates of the protopodite where they replace simple spines, while the
plumes are chiefly lateral. On the basal, or first segment, however, there is some-
what of a transition, since its proximal border is set with setae that extend out
to the tip as very long and sparsely branched plumes that thus extend close up
to the acicular setae. These latter under 4 D are seen to be set with very few
and fine side branches so that they are really somewhat plumose. The similarly
placed acicular setae upon the second segment, however, show no side branches
but are really smooth. The small tuft of setae already present in the first
stage at the base of the endopodite remains but little changed in the second
stage.

The second maxilla has undergone like changes (fig. 30). The terminal
spines of the first stage (fig. 10) are replaced by plumose setae and a few more
long plumes are added. Here again the plumose setae of the proximal edge of
the first segment extend' out as far as the acicular setae of the apex. The
endopodite has a few long plumose setae on its distal part in addition to the
cluster at its base. The scaphognathite is but little changed, the setae along its
outer edge being so bent down that they do not show their full length in the
view represented in figure 30. However, at the posterior tip of this respiratory

32 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

organ there is a peculiar growth of one or two setae. These are very long and
though appearing quite smooth and hair-like, with 2 D, they are seen to be really
set with short, fine side bristles, and they are sharp pointed. On the inner faces
of the four lobes of the protopodite there are now many long, sharp, curved,
setae.

In the first maxilliped (fig. 31) the process of substituting plumes and acic-
ular setae for spines has been carried on in the same general way. The cut-
ting edges of the protopodite now bristle with setae most of which are simple,
some straight, some with curved tips ; but the tendency to run the plumose seta;
up to the tip of the basal segment is carried so far that these plumes take
entire possession of this basal segment and only the second segment has acic-
ular seta?. Even on the second segment a few plumes come up nearly to the tip,
on the distal side. The endopodite bears but a few plumose setae while the
long exopodite has in addition to the former series of plumes along the outer
edge of the basal part (fig. 11) several remarkably long and conspicuous
plumes near its tip. The terminal part of the exopodite is cylindrical and tends
to become segmented and it is from its last and its penultimate segments that
the long plumes project and form a terminal brush. The flat epipodite scale
has still a few minute, blunt papillae along its posterior edge (figs. 31, 11), and
on its outer and inner edges a few of the remarkable exoskeletal hooks char-
acteristic of these organs.

The second maxilliped (fig. 32) has changed chiefly in adding plumes and
setae. The gills remain as before (fig. 12) but are longer. The protopodite has
added longer and more numerous plumose setae and a very few acicular ones.
The exopodite has substituted for its few terminal spines a brush of several
remarkably long, strong plumes (fig. 32), and for the sparse spines along the
outer edge of its basal segment a few setae which proximally are sparsely
plumed and distally smooth without barbs. The endopodite looks much changed
owing to the development of many long and stout acicular setae over its terminal
parts and inner edges. The setae of the endopodite are smooth as seen with
2 A, but with 2 D some five or six on the inner face of the second segment
and again on the distal edge of the fourth segment are finely barbed. In the
latter position two at the corner toward the exopodite have their fine lateral
branches flattened like saw teeth, so that they resemble the cleansing setae upon
the penultimate segment of the fifth leg of the adult, elsewhere described
(Andrews, '04). The fifth, or terminal segment of the endopodite, is armed
with long, smooth, stout, spine-like setae, with blunt points.

The third maxilliped has added but few plumes but many very long acic-
ular setae (figs. 33, 13). The plumes are a noticeable bunch at the tip of the
exopodite and a few on its basal part, as well as very few on the protopodite
and an increased number at the base of the epipodite. The gill region is now

THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBABUS 33

for the first time provided with the phenomenally long hair-like coxopoditic
setae found in the adult and in all but the first larval stages on this and all
the following thoracic somites. As seen in figure 33, these setae arise external
to the exopodite and add a conspicuous element to the appendages as they are
longer than the entire exopodite and coil about like stiff wires. The endopodite
bristles with exceedingly long, sharp needle-like setae and has no real plumes
whatever, though with 2 D" it was evident that some of the longest needles on
the terminal segment were very finely barbed. On the anterior, and inner,
face of that segment there were also numerous stout setae with flat saw-teeth
like those above described, on the corner of the penultimate segment of the
endopodite of the second maxilliped.

The chela (fig. 34) has greatly increased in size, as shown in comparing
with fig. 14, and now has simple acicular setae scattered over it but no plumose
sete. The terminal claw is no longer used as a holdfast and has no longer
recurved tips. Henceforth of use as a cutting shears it now bears a large tooth
on each blade as well as the rows of spines formerly present. At the base of
the appendage the gills have increased in size and there is a long tuft of coxo-
podite setae, which, however, are short in proportion to the enormous endopo-
dite.

The four walking legs (figs. 35, 36, 37, 38) though much larger than in the
first stage (figs. 15, 16, 17, 18) have not increased as much as have the chelae
and they retain their relative proportions and sizes. Like the chelae they now
bristle with acicular setae and show no plumose setae. However, at the distal
edge of the penultimate segment of the fourth and of the fifth legs (figs. 37, 38)
there are a few of the saw-like "cleansing setae" previously referred to as oc-
curring in the adult. The gills have changed only in size; the coxopodite set;e
are very long threads, but only few in number and on the last leg reduced to
one.

The branchial formula in the second stage was thus just like that above
given for the first stage.

On the abdomen of the second stage there were still but four pairs of ple-
opods since the first were not yet formed and the sixth still remained inside of
the telson. But each pleopod was now so well provided with plumose setae
that the appendage simulated a locomotor organ. The larvae also now had the
adult habit of swinging the pleopods back and forth and so producing currents
in the water which may well be of aid in respiration as they would change the
water supplied to the inhalent openings of the gill chambers. Each pleopod
(fig. 39) had grown greatly in length as compared with its first appearance
(fig. 19) ; the long plumose setae arose from the distal parts of the exopodite
and endopodite and resembled the plumes upon the exopodites of the maxillipeds
(figs. 31, 32, 33). The exopodite was still the longer and the endopodite the

34 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKTJS

shorter of the two flat lobes that bear setae so that the adult relationship in
size of these parts was not yet arrived at.

While the telson of the first larva was nearly circular, in the second it was
swollen laterally (fig. 23), and became thus transversely elongated since the
sixth pleopods had now grown within it as very large lateral masses. The
posterior edge of the telson was somewhat incised on the median plane and
thus recalled the early bilobed condition found in the embryo some days be-
fore hatching.

The long plumose setae of the telson (fig. 23) that aid the larva in swim-
ming are the expanded products of the radiating glands seen within the telson
of the first stage (fig. 20).

Thus provided with effective swimming setae and more numerous sensory
setae the second stage larva gradually depends less and less iipon its mother
and finally leaves her altogether. After some eight to ten days these active
larvae cast off their shells and passed into a third stage.

The third larva was in the main very like the second but it had advanced
a very important step in freeing its sixth abdominal appendages which hence-
forth are not inside the telson, but lying by the side of it to make the effective
tail-fan that is used in rapid locomotion. Some hours before shedding the sec-
ond larva plainly showed the sixth pleopods as dark red, partly opaque masses
within the base of the telson and after shedding these appendages were ex-
panded as is shown in figures 40 and 42. As both the end of the telson and the
edges of these great flat sixth pleopods are set with plumose setae the combined
fringe of setas augments the surface used by the larva in escaping backward
by vigorous blows of the telson and sixth pleopods against the water.

The details of this effective and very large sixth pleopod which has been
forming slowly on each side within the base of the telson ever since the larva
came out of the egg, that is from some two to three weeks, are shown in figure
42, which shows the dorsal face of the left appendage of. the sixth abdominal
somite. This appendage joins onto the sixth somite and lies by the side of the
telson as indicated in figure 40. The protopodite bears a prominent spine over
the base of the endopodite ; the endopodite is armed with two spines near its
edge and the exopodite with five spines, along the edge of the two segments into
which it is divided, as in the adult, by a movable hinge. Scattered over the sur-
face are a few relatively short acicular setae. It will be noted that the plumes
along the edges of both endopodite and exopodite are arranged to make a most
effective fan since those of the endopodite overlap some of those of the exopodite,
when, as in figure- 42, the exopodite is not extended as far as possible away
from the median plane. At times the exopodite may be shut in under the endop-
odite like a part of a fan.

The real length of the terminal plumes is somewhat greater than shown in

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 35

the figure since they are foreshortened there ; they do not stand out in straight
continuation of the plane of the telson and sixth appendage but are curved
downward so that their tips tend to point forward under the animal. The
entire fan is thus somewhat concave on the ventral side and in life the larva
carries its abdomen with its tip close to the substratum upon which it walks or
stands (fig. 41), and seen from above the fan is foreshortened. Both the habit
of carrying the fan inclined downward and the curved growth of the plumose
setae combine to make the fan a hollow scoop, which form would seem to be a
more efficient one for striking the water forwards and thus propelling the
animal backward. The forward bending of the setae by making it more difficult
for them to be forced back beyond the plane of the stiff parts of the fan would
seem to make them a more efficient addition to the striking surface.

The period of life in which the effective tail fan is formed by the libera-
tion of the sixth pleopods has hitherto remained unknown for the genus As-
tacus. Huxley ('80) says: "I imagine that the appendages of the

sixth abdominal somite are at that time (during the first ecdysis) expanded,
but nothing is definitely known at present of these changes." Faxon ('85)
records that specimen of Astacus pallipes 11 mm. long and ten days old still
had the sixth pleopods enclosed within the telson and supposed that they would
be set free after the second or third moult. Other observations seem to be
lacking.

The telson seen foreshortened in the natural position figure 40, is seen in its
true proportions in figure 43. From the circular form of the first stage (fig. 20)
it has passed through the transversely elongated form of the second stage (fig.
23) to its present complex and angular form. By an imperfect transverse hinge
it is now divided into an angular anterior part and a rounded posterior part.
The fact that this transverse division of the telson does not show till the third
larval stage is of interest in connection with the fact that this seems one of the
recent acquisitions of the highest crayfish. In the lobsters and other marine
forms, as well as in all the crayfish of the Southern Hemisphere, the telson is
not at all divided and amongst the Potamobine or higher crayfish of the North-
ern Hemisphere the division of the telson is much more perfect in the highest
forms, such. as Cambarus affinis, less pronounced in some lower forms as Cam-
barus Clarkii and in Astacus leniusculus, which is doubtless less specialized than
Cambarus, the division of the telson in the adult is by no means a perfect one.

In figure 43 are shown groups of acicular setae symmetrically placed right
and left; the rounded, terminal lobe is the only part bearing plumose setae.
These plumes stand in a single row and on the right and the left begin ante-
riorly as short setae followed by others that very soon are much longer and of
about constant length along the posterior border till near the median line when
there is a sudden falling off in length and one very short setas ends the series.

36 THE YOUNG OF THE CRAYFISHES ASTACTTS AND CAMBAEUS

Just dorsal to this row of long plumes there is a row of much fewer and re-
latively short acicular setae, shown in black in figure 43. In the reentrant
angle between the two lobes of the telson, each side, there is a rounded spine
similar to the one formed on the sixth pleopod (fig. 42) where the basal lobe
of the exopodite joins the distal lobe.

Beyond this perfection of the locomotor apparatus of the abdomen the
third larva differs but slightly from the second though there are differences in
size, proportion, color and habits. Comparing figure 40 with figure 23 it is seen
that the abdomen is wider, the cephalothorax more cylindrical, the limbs stouter,
the entire aspect more heavy and crayfish-like.

The third larva is still sufficiently transparent to allow the heart to be
seen through the shell, under the microscope, beating at about three times a
second; the stomach and intestines also show dimly as dark areas.

The animal is not conspicuous upon sand or mud; its color is, as before,
light with fine, dark-red specks. The eyes are black and the chelae not red but
pink. The liver region is greenish but the dark yolk so long conspicuous has dis-
appeared with the perfection of sensory and locomotor organs. Where
the head-thorax ends posteriorly there is a dark rim caused by concentration of
pigment cells there and the abdomen still has a dark band across the dorsal
side of the first somite. The region above the heart is quadrangular and very
pale in color. Back of each eye there is a dark longitudinal band. The groove
between the head and thorax dorsally is light and the pigment anterior to it
is more dense. Under the microscope the arborescent red pigment cells often
have a blue background and in some regions there are arborescent yellow cells
amongst the red ones.

The considerable increase in size in passing from the second to the third
stage may be seen by comparing the measurement given above, page 28, with
the following. In third stage a larva measured 14 mm. from rostrum tip to
edge of telson and 15 mm. 'to end of plumose setae. The antenna was 12 mm. and
the chela 10 mm. long. The width of the thorax was 3.5 mm. and its depth
4 mm. The telson was 2 mm. wide and the fan formed by it and the sixth pair
of pleopods 5 mm. without the plumose setae, and 6 mm. with them. The length
of the head-thorax was 7 mm. and of the abdomen 7 mm.

In the third stage the larvae were active and voracious, walking and swim-
ming with ease and speed so that they were hard to catch. When kept to-
gether they soon lost chelae in fight with one another and greedily devoured their
dead fellows. When a piece of frog's muscle was put into a dish with these
larvae they seized as soon as they came into contact with it and holding the main
mass with their chelae and other claws dragged it backward while tearing off
fragments with their moiith appendages. Thus twenty-three to twenty-five
days after hatching larvae in the third stage which had had no flesh food, unless

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 37

it were the chelae of other larvae, possessed well developed responses in the pres-
ence of flesh food. When meat was put on green ooze on the bottom of small
aquaria containing such larvae they showed no sign of being aware of it till in
contact with it when they seized it ravenously with their mouth parts and then
holding the mass with their chelae jerked back like a dog tearing meat from a
bone, so strongly as to pull off mouthfuls. When frightened away from the
meat, which was then placed one-third of an inch to one side of its former posi-
tion in the ooze, the larva returned to the place where the meat hud been and
seemed to masticate the ooze there and very slowly found the piece of meat
again as if through touch, taste, or smell and not at all by sight.

The pugnacity of the third larvae resulted in loss of limbs and specimens
with legs pulled off at the "breaking joints" and also rapidly regenerating
there were seen. Chant ran stated that larvae of Astacus would regenerate lost
limbs in seventy days while the adult males required one and a half to two
years and the females three or four years.

Excepting the newly expanded last abdominal appendages all of the append-
ages agreed with those of the second larva in most all details, but they were
larger. The first antenna, however, in place of the eight sense clubs of the
second stage, had eleven. These were placed as follows on the exopodite : four
in a group on the distal segment; three at the distal end and one upon the
middle of the under side of the penultimate segment; two at the distal end of
the antepenultimate segment and one at the distal end of the next segment. Just
as in the second stage the ear cavity was protected by a row of plumose setae
arching over it from its external border.

*%

The long filament of the antenna was often broken near the tip but contained
from 60 to 65 segments and some few of the terminal ones were constricted
about the middle as if they might divide at the next moult.

The acicular setae of the filament were about one-half as long as the seg-
ment, from the distal ends of which they arose in whorls of five or six. To-
ward the tip of the filament these setae were much longer than in the second
larva.

The mandibles, maxillae, maxillipeds, chelae, and walking legs with their gills
and setaj were the same as in the second stage except for increase of size.

Upon the abdomen the pleopods also were as in the second stage, except
in the case of the expanded sixth pair above described. As yet no appendages
were seen upon the first abdominal somite but as in this Astacus no ap-
pendages were found there in the adult female it may be that only female larvae
were examined. The four pleopods of the somite anterior to the sixth still had
the exopodite longer than the endopodite, as was also the case in the new sixth
pleopods (fig. 42). In the adult this relative size of exopodite and endopodite
is reversed in the abdominal organs that serve as secondary reproductive organs.

38 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

Thus in the male the first and the second somites bear the remarkable male
sperm conductors in which the endopodites greatly exceed the exopodites
or else form the only part developed while in the four following ple-
opods the larval relation is not much changed in the adult, as the exopodite
is as large as the endopodite or, in the sixth pair, larger, and in all these four
the function is not sexual but locomotor, or perhaps respiratory. In the female
the same state is found in the sixth pair, the first pair are lacking, while the
four other pairs have the endopodite much longer than the exopodite and both
are used as reproductive organs, as supports for the eggs and larvae.

Some of the larvje of the third stage were kept from May 18 to October 2,
and some of the moultings and increase in size noted, but no details of the
gradual completion of adult structure were studied.

The fourth larval stage was reached by a moult after the larva had lived
in the third stage twelve to fourteen days and was a little over one month old.
The length then increased from 15 mm. to 17 mm. The color was no longer
bright but dull and inconspicuous, pale grey densely spotted with almost black
pigment and scarcely any flesh color though the tips of the chela? were pink.
There was a marked transverse band of bluish across the posterior edge of the
carapace and the abdomen was much lighter than the thorax.

The fourth stage had advanced beyond the third in one important par-
ticular since now for the first time the appendages of the first abdominal somite
were seen in some specimens, which were probably males. These pleopods, how-
ever, were as yet but very simple rounded knobs which projected from the
sternal ridge of the first somite downward and decidedly inward, toward one
another, and were about one-tenth of a millimeter long.

At the end of June when the larvae had been in the fourth stage about a
month they passed into a fifth stage which was nineteen millimeters long
and in color red-brown or in some cases decidedly bluish. Kept in running
water with water plants and tubifex for food and at a temperature as high as
21.5° C., they climbed about actively upon the plants or else remained buried
in the ooze.

From some of the larvae left in a closed aquarium with algal ooze from June
16 to October 2, there remained one survivor five months and a week old that
measured 30 mm. in length, 6 mm. in width of thorax, 12 mm. in width of telson-
fan, and 25 mm. along the antenna. This crayfish having areas for the ends of
the oviducts upon the antepenultimate legs was a female, and it had no append-
ages upon the first abdominal segment. The color was bright, finely speckled
over with brown; the legs lighter; the antennae dark; the chelae purplish with
red and blue spots and there was still a blue transverse band across the poste-
rior edge of the thorax. The eyes were brown. The shell and flesh were stil 1
translucent so that the intestine showed through the dorsal side of the abdomen.

THE YOUNG OF THE CKAYFISHES ASTACUS AND CAMBAKUS 39

This larva buried itself in the ooze but was so active as to be caught with
difficulty. By October 20, it had shed and grown to a length of 34 mm., with
antenna 32 mm. long, so that with the food that had been given it it had
gained 4 mm. in length in eighteen days. This larva lived till February, 1905,
and died when nine months old.

Another lot of larvae kept in running water from July 16 to October 2, also
yielded but one survivor which had increased from less than 26 mm. to 55 mm.
and had a telson-fan 25 mm. wide, thorax 13 mm. wide, and antenna 36 mm.
long. This fine young crayfish five months and a week old looked like the adult
and was a male with well formed male stylets upon its first abdominal somite.
The body was opaque and dark ; greenish-blue and brown finely speckled ; the
legs lighter; the chelae with much blue and with the conspicuous flesh-colored
area that the adult has at the angle of the claw. The posterior edge of the
carapace was dark blue and the antennae were bluish at the base fading to
brownish at the tip. The under side of the body was pale flesh-color, or color-
less with some clear blue.

A third lot of larva1, 13 mm. long on May 27, and in the third stage, were
kept in more favorable conditions, that is, running water in a large tank, with
mud, plants, and sunlight, and on October 2 there were six survivors. The
measurements of these larvae, five months and a week old are given in the table
below :

Larva A B C D E F

Length 56 60 63 58 58? 52

Width 13 15 15 15 15 14

Antenna length ... 51 52 52 50 55 45

Sex $ 9 9 9 9 3

The males A and F had well formed male organs upon the first abdominal
somite while the four females had no appendages there, but the largest females
B and C had two blue spots upon that somite that suggested some connection
with a possible appendage. The colors of these large young were those of
adults, and though all reared in the same tank they showed individual differ-
ences in : general color, some being more dark olive, others brown ; in size and
color of the spot at the angle of the claw, which in one was reduced to a mere
light nodule and in others was a very large area; in color of under side of
claw which was dark or else bright flaming-red.

The eight young reared to an age of five months and one week thus
measured 30, 55, 56, 60, 63, 58, 58, 52 or an average of 54 mm.

Tabulating the facts above recorded as to the size and length of duration
of the larval stages as far as they were followed we find the following:

40

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

Stage.

Duration.

Length of
body.

Habit.

1

4-13 days

9 mm.

Fast to parent.

2

8-10 "

11 mm.

Free and gradually becom-

ing independent.

3

12-14 "

14-15 mm.

Independent.

4

30 '•

17 mm.

Independent.

5

?

19-20 mm.

Independent.

The number of moults necessary to increase the larva from the fifth stage
when about 20 mm. long to the autumnal larvae ranging from 30 to 63 and
averaging 54 is not known. The amount of increase at each moult above
tabulated was about 3 mm. In one case above cited a larva which had grown
only to 30 mm. in the autumn, when well fed quickly gained 4 mm. probably in
one moult. We might expect then an increment of 3 or 4 mm. at each moult, and
•growth from the 20 mm. length of the fifth stage to the average autumnal
length of 54 mm. may have taken from 8 to 11 moults thus making an estimated
total of 12 to 15 moults the first growing season. The size reached was, how-
ever, evidently determined in part by food. On such basis it may have taken
even more moults to produce the large autumn young 60 and 63 mm. long.
And at all events the above larva 30 mm. long having been kept in a closed
aquarium should be disregarded in reckoning the average. Rejecting this the
average for the seven others reared in running water would be 57. To attain
this average size it may well have required at least nine moults after the fifth
stage.

It seems then not improbable that this Astacus, under these conditions
moulted at least a dozen times while growing to a length of over two inches in the
first five months of its life. Four stageswere observed in the first two months
when the length had not extended to four-fifths of an inch, and probably twice as
many stages were necessary in the following three months to bring the length
up to over two inches.

The only previous records of the rate of growth of young Astacus seem to
be those of Soubeiran, Chantran, and Steffenberg. Soubeiran ('65) from
measurements of a crayfish in a French crayfish farm concluded that they did
not moult more than once in the first year, and were 50 mm. long when one
year old. Chantran ('70) thought the young crayfish moulted five times in 85
to 100 days of July, August, and September and no more till the end of the next
April. The first moult was at ten days after hatching and the other four at in-
tervals of twenty to twenty-five days each. These results were modified by
his further studies, also in the laboratory, and later ('71) he stated the number
of moults iii the first summer was eight and that the temperature influenced the

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS 41

number of moults so that there were six in the second summer, if hot. Finally
Steffenberg ( 72) gave the lengths of the Astaeus larvae in Sweden as B.5 mm. at
hatching; 11 mm. in the second stage; 13 mm. in the third stage; 15 mm. in the
fourth stage.

Astaeus leniusculus thus agrees closely with the Astaeus of Sweden in the
length of the larva in the first, second, third, and fourth stages. As far
as the facts go it seems evident that Astaeus leniusculus probably has more
larval stages than have been described for the first year young of the French
Astaeus, but the differences are probably due more to difference in food and
in temperature than to any innate differences in the species.

With this close agreement in larval life between the American and Euro-
pean Astaeus and the demonstrated success of rearing in the laboratory the
large young from the eggs brought overland, the culture of the American As-
taeus should be as successful when undertaken as has been crayfish culture in
Europe. As elsewhere remarked (Andrews, :063; :064) the introduction of
the western Astaeus leniusculus into Eastern waters might not only prove of
economic value but also help to throw light upon the interesting problem of the
nature of the causes that have brought about the present remarkable geograph-
ical distribution of crayfish. And the geographical distribution of crayfish is
intimately connected with the origin of species in this group.

CAMBAEUS AFFINIS.

As elsewhere described (Andrews, :04) this common crayfish of Maryland
and adjacent States lays its eggs in the spring, and the development of the
young can be followed in the laboratory. Preparatory to laying, the females
carefully cleanse the parts of their bodies to which the eggs are to be attached
and the eggs flow out of the oviducts into a mucous mass which covers the ple-
opods upon which, after some special "turning" movements of the female, the
eggs are found attached each by its own stalk (Andrews, :06).

The hatching young thus find themselves upon the abdomen of the parent
and here, as in Astaeus, there are special contrivances which prolong the connec-
tion of parent and offspring for some time after hatching so that the attainment
of a free and independent existence is a slow and gradual process.

The special arrangements used in the attachment of the egg and of the larvae
in the first and second stages form a series of interesting adjustments between
the adult and the next generation. These successive means of association of
mother and offspring will be described in what follows.

We will first consider the egg and the maternal appendages.

The eggs, while numerous, three to six hundred according to the size of the
female, are small, scarcely 1.5 mm. as compared with 2.5 mm. in Astaeus len-
iusculus. Some few become fastened to setae upon the abdominal sterna but

4

42 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAEUS

most are fastened to plumose hairs upon the pleopods of the second to
fifth somites inclusive, and some account of these pleopods may be given here
in connection with questions as to how the eggs and larvae are attached to the
mother.

The posterior face of the fourth left pleopod of a female about to lay is
represented in figure 44. It will be noted that the endopodite is longer than
the exopodite, and both bear a fringe of long plumose setae on their right and
left edges. The setae are shorter toward the base of the exopodite and of the
endopodite while on the protopodite there are but a few plumose setae in two
tufts upon the inner edge. The long setae make of the pleopod a wide fan or
flat brush since the setae lie close together and like the wing feathers of a bird
form a rather flat firm expanse. The protopodite has a basal part containing
several calcified plates in a soft membrane, and a long segment that is well
calcified except for a triangular soft area toward its base on the posterior face.
The endopodite is made of two segments and the exopodite of one. The endopo-
dite and the exopodite are also somewhat annulated in appearance owing to
the grouping of the cement glands. The groups are opaque white and from each
side tend to run together across the posterior face. Distally they do not meet
but proximally they meet and make cross bands. Still farther toward the base
the glands cover the entire surface more and more completely. The non-gland-
ular areas are clear and not opaque, and in the figure are represented dark.

The anterior face differs from the posterior (fig. 44) in a greater de-
velopment of glands which formed transverse bands more nearly all the way to
the tip. As so many of the glands are to the right and left near the setae, they
are well placed to smear their secretion over the set*.

Toward the tips of the pleopods the exoskeleton is so translucent that with
Zeiss 2 D, the striation of the muscle fibers, the branched connective tissue
cells, granular blood corpuscles, and the polygonal gland cells may be seen.
The gland cells are about the diameter of a muscle fiber and larger than a
blood corpuscle.

In most cases the plumose setae spring from over the glands, and the base
of a seta is as thick as two gland cells. The setae have a large central cavity
and a thick wall which is highly refractive and clear and is of unequal thick-
ness so that it projects into the cavity in lumps or waves, and gives the distal
part of the axis of the seta a somewhat segmented aspect. At the base each
seta is. articulated to the exoskeleton, and its central cavity is constricted by a
clear refractive thickening of the wall that leaves very little communication be-
tween the cavity of the setae and the cavity of the body.

The side branches of the seta spring out not only along its sides but also,
scatteringly, along its posterior face so that the plumose seta is more like a
bottle brush than like a flat feather. While the side branches generally make

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 43

a wide angle with the main axis, toward the tip they become more nearly par-
allel with it and thus a fine terminal brush is formed by the main axis coming
gradually to an acute point in the midst of the surrounding side branches.

The eggs are fastened to these plumose hairs by a secretion that probably
comes out of the glands of the pleopods (Andrews, :062). They then look as in
figure 45, which represents the anterior face of a pleopod cut off in the afternoon
of April 18, 1905, from a female that had laid the night before. Most of the
pleopod is concealed by the eggs which are opaque yellow balls and very elastic.
The plumose setae are all bound together by a common cement or mass of glaire
so that the individual setae are not seen. From this mass a clear, flat, glassy
band of material goes out to each egg. Upon separating the eggs these bands
are seen as clear, flat stalks, continuous at one end with the mass that binds the
setae together and at the other end with the envelope about the egg. While the
shorter bands are flat and wide the longer bands are more string-like and some
few are twisted. Though these stalks may cross one another and be more or
less intertwined they are not fastened to one another. As the setae spring
chiefly from the side of the pleopod and the eggs are tied to the setae, the eggs
may be combed out, as it were, into groups on each side of the endopodite
and of the exopodite. Where the stalk joins the egg it is enlarged as a bell, or
tent, full of liquid and its edges are continuous with the outer layer of the egg
capsule.

Each egg had then its own separate stalk, though a very few exceptions
showed two stalks connected with an egg at different points and with a com-
mon extension running over the surface of the egg from one stalk to the other.

Thus very firmly attached to the mother, the eggs are waved back and forth
by the mother who regulates the movements of the pleopods in accordance with
the oxygen supply in the water, and thus they slowly develop till they hatch.
The old egg cases and stalks still remain fast to the pleopods, and are of
use to the larva as a means of prolonging its life of dependence upon the
mother.

We will next describe the way in which the first larva is connected with
the mother.

In hatching, the larva comes slowly out of the egg capsule through a rent
along its back, in such a way as to draw out the legs and abdomen last of all as
represented in figure 8 in a previous paper (Andrews, :04). In fact the tip of
the abdomen remains inside the egg case long after the soft, helpless larva is
extruded and left dangling down into the water. And all these newly hatched
larvae would fall to the bottom were it not for a firm attachment of the tip of the
abdomen inside the egg case. As it is some time before the respiratory move-
ments become perfect, as the limbs only gradually acquire ability to move, and as
the body is globose and the creature cannot stand on its legs, the larva would

44 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

probably perish but for this temporary fastening of the abdomen that tides it
over the weak period till it can reach up and take hold of the egg stalk as in-
dicated in figure 9 of the above paper.

This attachment of the abdomen is the same phenomenon found in Astacus
and is brought about by a telson thread ; but as the eggs and larvae of Cambarus
are so much smaller and as the tip of the abdomen remains inside the egg cap-
sule the facts are not so readily made out and in a previous notice (Andrews,
:04) the telson thread was spoken of as proceeding from the anal region, though
further study shows it to be fastened to glandular spines of the telson edge as
in Astacus.

In Cambarus affinis the tip of the abdomen is fastened by a short thread to
a crumpled membrane which lies inside of the spheroidal egg case and is firmly
fixed to the egg case on the side near the stalk. The short thread and the
membrane together are comparable to the long membranous thread that in
Astacus allows the larva to hang far down from the egg case. For conven-
ience we will describe the two parts of the telson thread separately. The short
part fastened to the abdomen remains on larvae 48 hours old though then broken
off from the more membranous part inside the £gg case. The short part may
be whipped up and down in the water like a lash when the larva flaps its abdo-
men (fig. 50).

At hatching, the telson (fig. 46) is a simple rounded, translucent lobe, with
minute spines on each side of the median plane, which formerly fastened it to
the telson thread. In this ventral view of a recently hatched larva the pleopods
of the fourth and fifth somites are seen free while the sixth somite has its pleo-
pods as lobes inside the telson on each side of the anus. The terminal part of
the telson is traversed by radiating lines which point to spines along the edge of
the telson. These lines are in reality rows of cells that are to make the
plumose setae of later larval stages and the rest of the translucent flat telson is
filled by a parenchymatous mass traversed by blood spaces in which float blood
corpuscles.

The telson thread arising from the edge of the telson is a flat band that is
readily twisted and shows a striation due to fine wrinkles of the stiff chitin-like
material composing this very strong but thin and translucent membrane.

Twenty hours after hatching, the telson had changed form, become more
quadrangular and its terminal part was somewhat three lobed (fig. 47). And as
the spines to which the telson thread was attached were all on the middle lobe
it seemed as if the pull of the telson thread might have aided in making the
middle region protrude as a lobe. At this time the cuticle of the larva was
separating from the body in preparation for the moult from the first to the sec-
ond stage.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS 45

While the form of the telson is thus so different from that of Astacus (fig.
20), the mode of attachment of the telson thread is fundamentally the same.
Figure 48 shows the tip of the telson of a larva torn out of its shell just before
hatching ; the thread is fastened to five or six spines on each side of the median
plane in the same way as in Astacus (fig. 21). Thus nearly the same number of
spines are specialized in both crayfish for attachment of the thread though in
Cambarus affinis the entire number of spines is much less and they are found
only on the posterior part of the edge of the telson.

All the spines are glass clear, ice-like in refraction; the lateral ones are
bent toward the tip of the telson and the five or six specialized glandular spines
converge toward a center as shown in figure 48. The lateral spines toward the
posterior end tend to show blunt brushes and secreted lobes at their tips, and
thus form somewhat of a transition to the effective specialized spines.

These specialized central spines are much longer and thicker and bent,
often at right angles. Some are fused together by their blunt ends and all
seem to have flowed out at the tips as a mass which is now fibrous and which
binds all of them to each other and to the telson thread. They seem compar-
able to paste tubes which should squeeze out a myelin-like substance that could
coagulate as strong fibrils.

The appearances suggested that the rows of gland cells that later make the
plumose setae of the later larva, had previously, in late embryonic life, secreted a
substance which oozed out of the hollow spines and set into a firm cement; but
these cells no doubt were also active in making the cuticular walls of the spines
themselves, and no sharp line seemed drawn between the substance of the
cuticular spines and the material that issued out of their tips. Both are pre-
sumably the same exoskeleton and made from ectoderm cells that later make
other exoskeletal secretions in the form of plumose setae. In Astacus (fig. 21)
the distinction between spine and secretion was more evident, but in this Cam-
barus (fig. 48) the spines are so minute that details are not as readily seen.

While the mode of attachment of the telson thread to the telson is thus the
same in Astacus and in Cambarus, the thread itself differs in appearance in
the two crayfish, in the former being pulled out into a long thread, in the
latter being for the most part a wrinkled mass of membrane within the egg
case. While in Astacus the thread is apparently a cast off embryonic skin, this
is by no means obvious in Cambarus and an interpretation of its meaning was
had only from the following facts. When an egg ready to hatch was scratched
with a needle the outer egg case came off and the larva popped out alive but
still enclosed in a thin spheroidal membrane. This membrane was firmly
fastened to the outer egg case by one small area towards which the legs con-
verged and which lay opposite the claws. When the egg case was pulled it re-
mained so fast to the membrane that both wei-e drawn out of shape rather than

46 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

separate. The part of the egg case attached to the membrane was often near to
the stalk of the egg case, which led one to infer that the attachment of egg case
and membrane and the making of the egg stalk might have some common
cause very early in the life of the egg, but no observations were made to de-
cide this. Left to itself a few minutes, such an embryo removed from the shell
burst the membrane without the aid of the egg case. Its telson was fastened
by its special glandular spines to the inside of the membrane, and soon it
reached about with its claws and seized hold of the membrane. This bag-like
membrane was thus the same thing as the telson thread of normal hatching.
When dissected from an embryo this membrane was seen to be a bag fast to
the telson spines, but with no observed special envelopes for the limbs as would
be the case were it a cast skin. Before hatching, the membrane was stretched
tightly all over the abdomen except where the two special groups of glandular
telson spines were, and there the membrane was raised up as two swellings,
one right and one left, much higher than the spines themselves. The space be-
tween the membrane and the spines was occupied by a mass of seemingly
liquid lumps which in some cases with 4 D showed a finely fibrous material
amongst the clear spines which, in places, extended out to the membrane like
a fibrous coagulum binding the spines to the membrane. On the median line
the membrane was close down against the telson so that the secreted masses
right and left seemed to have locally pushed the membrane away from its
original connection with the telson.

This membrane was well developed in embryos of stages J to K of Reich-
enbach but upon dissecting, these embryos dropped out of the membrane, as
the telson was then not yet fast to the membrane, though the membrane was
firmly fastened to the egg case near the stalk. In the early stage F there was
also a membrane over the body and this was loose over the slightly projecting,
small abdomen.

It seems probable that the telson thread of Astacus, which is a cuticle
formed over the embryo when its limbs are well advanced and thus has tubular
outgrowths to cover the limbs, is represented in Cambarus by a telson thread
having the form of a sac-like membrane formed so early that the small limbs
receive no special envelopes. In both cases there is a special outgrowth to cover
the abdomen, but while in Astacus this is a long bag, in Cambarus it is scarcely
recognizable as a separate region.

In both, by some unknown process that is imagined to be associated with
fertilization phenomena, the membrane is made fast to the outer egg case, and in
both the membrane becomes fastened to the embryo by the activity of certain
telson glands. A diagram of Astacus would represent it as escaping from a
cuticle when hatching, a cuticle fastened to the egg case at one point, and near
that point fastened, inside, to the telson of the larva. A diagram of Cambarus

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 47

would represent it as casting off a membrane at hatching which is fastened as
in Astacus but lacks the tubular coverings for the limbs. Here again the small
size of Cambarus may have led to misinterpretation of what is plain in As-
tacus.

Having described this temporary, mechanical association of parent and
young we will next consider the more active association that lasts during the
rest of the first larval period.

The larvae, supported for a time by the telson thread, soon established
a second connection with the mother by seizing hold of the egg case, the egg
stalk, or in many cases the matted pleopod setae, with their chelae, and thus, for
a time, were fastened both by the telson thread and by the chelae. While the
eggs hung loosely from the pleopod, figure 45, the young crayfish had the
habit of reaching in their chelae as far as possible amongst the egg stalks
and pulling themselves close to the pleopods so that they became densely
crowded together in a solid mass (fig. 52). In life this mass of young cover-
ing the pleopod is a curious sight suggesting mammalian young crowding for
maternal milk. Each held itself close to the pleopod, and when disturbed
drew itself all the closer as if eager to remain. The part exposed to view is
chiefly the rounded head-thorax which is flesh-colored but is conspicuously
marked by the enclosed saddle-shaped dark yolk. Here and there the legs and
abdomen are seen in profile (fig. 52), but generally the abdomen and legs are
under the body, the abdomen being bent somewhat as in a brachyuran (fig. 50)
and a full dorsal view shows chiefly the simple head- thorax (fig. 49). The larvae
thus seem egg-like, inert and inactive.

The long-stalked egg cases stand out above the backs of the larvae as do also
a few belated eggs which may hatch some forty-eight hours after the rest (fig.
52). By this time many of the larvae have broken the telson thread and when
disturbed make slight movements with their legs and flap the abdomen to which
is fastened, like a small handkerchief, the narrow telson end of the thread, while
the membranous sac remains within the egg case.

So closely do the larvae crowd together that only few of the pleopod setae
can be seen. Figure 52 represents a case in which some of the larvae had been
removed.

While the color of the first larva is light flesh-color to the naked eye, under
the microscope the creature is clear, and colorless, except for the scattered,
arborescent, vermilion pigment cells over the carapace, abdomen, basal parts of
antennae and some few segments of the legs, and except for the reddish pig-
ment in the eyes and for the large red-brown yolk mass.

The shape of the larva when alive is retained very well in specimens killed
in Worcester's liquid, though in many other liquids the head-thorax swells and
is abnormally glubose, while the branchiostegites roll back and expose the gills.

48 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

In neither the dorsal nor the side view (figs. 49, 50) can the rostrum be well seen,
but in a front view (fig. 51) it is seen to be pointed, though so bent downward be-
tween the eyes as to be of no use as a protection.

The body is thus rounded and embryonic in proportion and lacks all the
angularities of adults or of active larvae.

With the clinging helpless state of the larvae is associated a lack of ordinary
use of the antenna?. The second antenna?, which in larval and adult life of crus-
tacea are carried out in front of the animal, are here folded down under the
thorax (fig. 50), between the right and left series of legs. This peculiar posi-
tion of the antennae is not found in Astacus and here is brought about at the
time of hatching, for in the embryo these antennae grow backward along the
edge of the carapace external to the bases of the limbs. Soon after hatching the
legs get astride the antennae and this apparently useless position of the antennae
is maintained during the rest of the life of the larva in its first stage.

This peculiar position of the antennae as well as the down bent rostrum
were observed in another species of Cambarus, C. rusticus by Faxon ('85);
and later Steel e (:02) described the rostrum as bent down in C. gracilis and
in other species and the legs, antenna? and abdomen of C. virilis as lying under
the thorax; thus it seems possible that the first stage of Cambarus in general
differs from Astacus in these characteristics of the antenna.

The appendages of C. affinis in this first stage resemble those of Astacus
leniusculus in being without the setae of later stages, but they differ not only ill
being very much smaller but in being, in some cases, more simple. Thus the
first antenna (fig. 53) has only four segments in the endopodite and in the ex-
opodite in place of five, and the tip of the endopodite bears no sensory club.

The antenna (fig. 54) is remarkably short, as is seen on comparing that
figure with figure 7, and figure 50 with figure 3. The filament is bent back and
has but twenty-five segments, or about half as many as Astacus. In the adult
there may be 150 segments. Carried as it is under the thorax it reaches only
to the beginning of the abdomen while in Astacus the antenna if in such a posi-
tion would reach about to the end of the abdomen when stretched out.

The mandible (fig. 55) has the same simple form as in Astacus (fig. 8).

The first maxilla (fig. 56) is like that of Astacus (fig. 9), but more simple
in lacking the few filose setae and in having fewer spines.

The second maxilla (fig. 57) as in Astacus (fig. 10), has a row of plumose
setae along the entire edge of the scaphognathite and is elsewhere as simple.

The maxillipeds (figs. 58, 59, 60) represent in miniature the structure seen
in Astacus (figs.Vll, 12, 13) with slight increase in smoothness due to the pres-
ence of fewer setse and spines. There are important simplifications, however, in
the gills which in some cases have but half as many side filaments as in Astacus.

The chelae (figs. 61, 62) have the same recurved tips as in Astacus. Soon

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

49

after hatching the larva opens its claws widely (fig. 50), and after some failures
fastens them to the egg stalk, or to the setae of the mother's pleopods. Once
firmly locked in the hardened secretion that makes the egg stalks and binds the
setae together, these larval chelae remain fast during the first stage. And even
after the larva has escaped from its cuticle and passed into the second stage
the old cuticles are left firmly hung to the mother by the cast-off chelae.

As in Astacus the chela has at first a cutting edge set with a row of few
and simple spines, but when the first larva is ready to moult, the loosening of
the cuticle reveals the fact that each spine will be replaced by one that is ser-
rated (fig. 62), owing to the presence of flat plates along the posterior face of
the new spines. In addition the second stage will have on its claw some spines
not represented in the first stage and also near the tips of the claw some long,
simple setae in place of the blunt spines there in the first stage. This figure
shows that the recurved tips will be abandoned in the second stage since
there are already formed tips that are but slightly curved hooks, to take the
place of former recurved tips, one of which was broken off in this specimen.

The chela besides being so small and weak, is inferior to that of Astacus
in having its gills less developed, the anterior arthrobranch being very short
and simple and with but few side filaments.

In the four walking legs (figs. 63, 64, 65, 66), we find the same proportions
as in Astacus but the pleurobranchiss are absent and the arthrobranchijE are
more simple, especially the anterior ones.

The branchial formula for the first stage is thus the same as in the adult
and is as follows :

Podo-
branchife.

Arthrobranchise.

Pleuro-
branch ife.

Total.

Anterior.

Posterior.

Somite of 2d inaxilliped

1
1
1
1
1
1
0

1
1
1
1
1
1
0

0

1
1
1
1
1
0

0000000

2
3
3
3
3
3
0

Somite of 3d inaxilliped
Somite of chela
Somite of 1st walkin*** le^1 ....

Somite of 3d walkin<r leg

Somite of 4th walking leg ....

6

6

5

0

17

That the pleurobranch of the last thoracic somite of Astacus was absent
from Cambarus rusticus larvae 4 mm. long and evidently just out of the egg
was observed by Faxon ('85) and it is probable that no members of the genus
Cambarus have remnants left in the early larvae of that pleurobranch still found
in Astacus.

50 THE YOUNG OF THE CKAYFISHES ASTACTJS AND

As in Astacus the abdomen in the first stage of C. affinis, just as in some
other species of Cambarus studied by Faxon ('85), has only four pairs of evi-
dent pleopods. The sixth pair are but partly formed and enclosed within the tel-
son while the first pair exist here as minute buds readily overlooked and not
found in Astacus nor as yet described in other species of Cambarus. The four
evident pleopods (fig. 67) have equal exopodites and endopodites in contrast to
the proportion found in Astacus (fig. 19). The beginnings of the first pair of
pleopods are but minute rounded elevations of the sternal ridge of the first
somite (as indicated in fig. 3; Andrews, :06), and contain a small mass of nu-
cleated epidermal cells. The appendages of the sixth somite are large internal
buds that cause the side part of the telson to be very thick as they fill all its
interior on each side of the anus. As this region is very translucent each
pleopod can be seen to have a long outer and a. short inner lobe (figs. 46, 47).

The first larva is in several ways more imperfect than the same stage in
Astacus, and as it lives inactive and fastened to the maternal pleopods it seems
but an extension of the embryonic period in preparation for the second stage,
and not at all a self supporting organism. The second stage is made way for
by the gradual loosening of the cuticle of the first stage, as above noted in case
of the claws of the chelae, and by the addition within the old cuticle of the new
exoskeletal structure of the second stage. This was evident in the telson of a
larva twenty hours after hatching, where the old cuticle was raised up the length
of the old telson spines and new spines had grown out across this space to enter
the hollows of the old spines. Later, just before the moult, the space between the
old and new cuticle was twice the length of the old spines, which were still
fastened to the remnant of the telson thread, and the new spines still projected
across the space into the old hollow spines.

The moulting into the second stage took place after the first stage had lived
this dependent and preparatory life for about forty-eight hours and the larva
resulting had the form shown in figures 68 and 69. These second larvae unlike
the second stage of Astacus did not gradually become separated from the
mother and live isolated, but remained again adhering to the pleopods till a
second moult brought them into the third stage which was the first free larval
form. Thus the pleopods were still covered with the crowded larvae. Figure
70 represents a pleopod with only part of its load of second stage larvae as
many had been removed.

In the following description it will be shown that in the second larva also
there is a peculiar temporary mechanical connection of young and parent.

Each pleopod in life was covered as with a mass of animated jewels of
pink and garnet colors. The flesh-colored larvae were still strongly marked by
the yolk that remained in each as a garnet red mass of saddle-bag shape. No
longer firmly fixed by the chelae, the larvae soon reached about for firm objects to

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAEUS 51

••

which to hold, or kicking their legs about, swinging their pleopods and flap-
ping their abdomens formed an animated restless mass quite unlike the inert
one seen in the previous period. Thus active, though holding fast, the larvae
were no longer densely crowded in close to the pleopods as in the first stage (fig.
52), but loosely aggregated (fig. 70).

The old larval cases shrivelled and not readily recognizable as more than
crumpled membranes, still remained fast by their chelae and the old egg cases
were yet fixed by their stalks to the maternal pleopods. Side by side on old
egg stalks were the pairs of living claws and the empty cuticles of old cast off
claws. Thus the second larvae lived amidst a mass of former envelopes, — the
ghost-like phantoms of their former selves and the rigid cradles of those selves.

While many larvae holding fast to the pleopod hairs and to egg stalks tend
to pull themselves in close to the pleopod so that they become buried amongst
the egg stalks and empty cases, a few larvae at the periphery of the mass may
dangle free in the water, as in the lower right corner of figure 70. These are
larva; which have recently cast off the first cuticle and are still in a soft, help-
less condition. Before these larvae succeed in reaching up and seizing hold of
some part of the general mass they are in danger of falling to the bottom where
they might be lost, though when they are removed it is found that they can stand
and walk, with difficulty. However they seem strongly controlled by an instinct
to climb, crawling over one another in heaps when removed from the mother and
swimming only when thrown into Perenyi's liquid and possibly many would
eventually climb up onto the mother. At all events they are prevented from fall-
ing away from the mother by a fine thread which, as indicated in figure 70,
passes from the posterior end of the larva to the crumpled, cast-off cuticle
which still is firmly fixed to the mother. This thread may be called the anal
thread since it actually conies from the anus and not from the rim of the telson
as did the supporting thread of the first larva.

But before discussing this anal thread some general features of the second
larva may be considered. The abdomen is still carried bent down as seen in
figures 69 and 68, but the cephalothorax is more elongated and narrow than in
the first stage and ends in a sharp pointed toothed rostrum that projects out be-
tween the eyes and is only slightly bent down. The legs are longer and may now
be used for walking and the antennae stand out in front of the animal as if use-
ful feelers, in strong contrast to their apparently useless position in the first
larva (fig. 50). This increase in length and change of position of the antennae
gives the mass of young in the second stage (fig. 70) a much more living aspect
than was possible in the first stage (fig. 52). The abdomen when straightened
out is seen to end still as a simple rounded telson (fig. 71) with the large sixth
pleopod still within it on each side the anus and with a terminal part that has
its middle lobe set off but slightly from the side lobes. The edge of the telson

52 THE YOUNG OF THE CBAYFISHES ASTACTJS AND CAMBARTJS

bears only simple spines as in the first stage (fig. 46), and these spines are not
divided into groups (fig. 72), but all seem equally useless since none act as
glands and there is no telson thread formed in the second stage. The middle
lobe bears spines all along its edge, some sixteen on each side replacing the
fewer spines of the first stage (fig. 48). Passing in from each spine there is
still a radiating line of cells which is active in making the plumose setae which
we miss in this second stage but which will be expanded in the third stage.

It is to the larva of the above structure that the anal thread is fastened
and this may now be considered in connection with this telson that has pro-
gressed so little beyond its first form. As seen in figure 71, the anal thread
was in life a clear narrow ribbon running from the anus a distance greater
than the length of the telson to be fast to a crumpled mass which proved to be
the cast-off cuticle. This thread was fast at one end inside the intestine of the
larva and at the other was fast to the cast cuticle by being continuous with it
at the edge of the cast off anal opening. In fact the anal thread is nothing more
nor less than the old cutrcular lining of the intestine of the first larva still con-
tinuous with the cast-off cuticle of the abdomen and not yet entirely loosened
from the intestine of the second larva. An examination of the recently shed
larva showed that the cuticle of the larva had become loose all over the body
and some distance into the intestine, but that farther in it still adhered to the
epithelial lining of the intestine.

When the larva has moulted, the old cuticle of the abdomen is found to be
telescoped and its old telson joined by a short cord to the new telson as shown
in figure 73 ; A. If the old cuticle is then pulled with forceps it does not break
loose but the thread comes out of the anus of the larva and is thus made longer,
as shown in figure 73 B, by a shortening and crumpling of the intestine. There
is thus a posterior part of the intestine (y) in which the old cuticle is loose and
an anterior part (x) where it is still fast, the region (a) being the first place
met with where the cuticle lining of the intestine does not pull away from the in-
testinal wall. Hence the region (y) is thrown into folds and the region (x)
stretched and pulled bodily toward the anus when tension of the anal string
pulls the region (a) toward the anus. The anal thread is the loose lining of
the intestine as far as it is pulled out of the anus and while in origin a tubular
cuticle it is stretched out as a flat ribbon which seems made of clear wire-like
fibres, but in reality is only thrown into longitudinal folds due in part to the
longitudinal ridges which sections show are present in the intestine. In figure
74 is seen more enlarged the region of the intestine where the loosened cuticle
running up from the anus arrives at the region («) where it is still fast to the
epithelial walls, as made out in preparations cleared in Bela Haller's liquid.

Though actual ecdysis was not seen, it is evident that what happens in the
moulting of the first larva to the second stage, is that the lining of the intestine

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 53

for a certain distance up from the anus, delays in casting off its cuticle. The
animal bursting out of its head-thorax cuticle and freeing its limbs from their
cases would next pull its abdomen out of its old cuticle, but the old cuticular
lining of the intestine remains firm where continuous with the outside cuticle at
the edges of the anus, and acts like a string tied to the old telson and to the inside
of the abdomen far up in the intestine. If the larva then drops out of its cuticle
and is too weak to seize hold of the old cuticle, or neighboring firm objects, it
will dangle suspended by the anal thread and the tension on this thread will
pull it out of the anus as far as possible. By puckering the posterior part of the
intestine and by dragging the anterior part of the intestine backward there is
thus drawn out of the anus an anal string which, however, is not as long as
the abdomen, by any means. The old telson being a stiff plate and the old
walls of the abdomen being elsewhere like the bellows of a camera, the pull
of the weight of the larva along the telson thread drags the old telson against
the cast-off abdominal rings and telescopes the abdominal cuticle as if the front
board of a camera were pulled back against the bellows by a string inside. The
tendency of the telson string would be to turn the abdominal cuticle of the cast-
off case inside out as a hand holding fast to a sleeve would turn the sleeve
inside out when the arm was withdrawn, but the presence of a firm, board-like
telson at the bottom of the sleeve allows only a telescoping of the cuticle. By
this means the old abdominal walls are so shut up that the free anal string
from the old anus to new anus is no longer inside the old abdomen, but largely
free in the water, as indicated in the diagram on page 54.

Soon after hatching, presumably, the cuticular lining of the intestine be-
comes loosened along the regions (a) and (x) and then the anal thread is
pulled out from the intestine as is usual in moulting. In the meantime the larva
becomes strong enough to reach about and take hold of the old larval skin or
of other objects fastened to the pleopods and does not need the anal string as
a means of support.

By this delay in the casting off of part of the cuticular lining of the in-
testine an advantage to the larva seems to result. Both in the first stage and in
the second stage the larva has a mechanical means of fixation to its mother
during the brief period when it is unable to use its claws for this purpose.
Reviewing the life of the crayfish up to the third stage with the aid of a rude
diagram (page 54), with reference to the association of mother and offspring, we
have seen : the egg fastened to the pleopod setae by a material that hardens soon
after the egg is laid; the larva hung for awhile by its telson thread; then
holding by its claws as well as telson thread till the latter breaks when claws
alone hold it locked to the mother; then dangled loose as a helpless second
stage supported by an anal thread till able to take hold with its claws and cast off
the thread, that is, to finish the moulting ; finally moulting again and as an active

54 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

third larva living no longer mechanically bound to the mother, with whom it
gradually ceases to associate. The mechanical supports, the telson thread
and the anal thread, are left hanging with the egg stalks, egg cases and the other
part of the cast off membrane and cuticle; all fast to the pleopod sete which
are bound together in a secreted mass. All this material soon disappears,
apparently being eaten up by the third larva before it leaves the mother to
hunt other food in wider fields.

J

PL

m.

EXPLANATION OP DIAGRAM.

PI. = pleopod of mother; PI. H = setre of pleopod; l=cast cuticle of first larva; St. = egg stalk .
Sh. =egg shell; M. = membrane inside shell; Tf. = telson thread, which is broken; Af.= anal thread;
= second stage on the mother's pleopods held by anal thread till the claws have taken hold.

Of the two threads which we here describe as mechanical means for pre-
serving the association of the mother and offspring and prolonging the ma-
ternal protection beyond the egg stage over larval periods that are especially
helpless and not self supporting, the first, the telson thread, is a secretion of
glands active before the larva hatches combined with an adherence of the larval
envelope to the egg shell that was determined very early in embryonic life.
The second thread, the anal thread, is a much more simple and temporary
attachment brought about by a delay in casting off the cuticular lining of the
intestine and thus utilizing what is cast off as a means of keeping the larva
fastened to its old cuticle till the claws can lay hold of some firm object.

When the second larva finally becomes fastened by its claws it remains
some six days in a condition of. little activity. It is dependent upon the mother
for physical support though in a state intermediate between the invariably
fixed first larva and the wandering third larva. The shape of the claws (fig.
84) shows that they would not become as firmly locked as did the claws of the
first larva (figs. 61, 62), though they might stick firmly into soft material.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 55

When larvae in the second stage were put into Kleienberg's picrosulphuric they
flapped their abdomens for some minutes but did not loosen their claws from the
pleopod of the mother; when put into alcohol, however, they dropped off, and
when into Worcester's liquid they all broke loose and fell to the bottom
where they lay kicking their legs for some time as they were not so readily
killed as were the third larvae.

The second larva lives much as did the first larva and in structure is very
like it but it differs not only in the above mentioned characteristics of the telson
and mode of fixation to the parent but also in the size, proportions, and amount
of armament with setse of some of the appendages as will be seen when the
nineteen pairs of appendages are taken up in sequence.

The first antenna (fig. 76) has grown much longer than it was in the first
stage (fig. 53), and the basal segment of the exopodite has divided into two so
that there are now five in place of four segments. And as the figure shows
there are now a few sette upon endopodite, exopodite, and protopodite and of
these there are five blunt sensory clubs on the inner face of the exopodite. Two
of these are close together on the distal end of the fourth segment, two are close
together on the swollen basal half of the fifth and the remaining one stands
alone on the narrow terminal half of same segment. The ear is still a
simple deep pit without as yet any setae along its edges but with only seven or
eight spines or teeth seen with 2 D along its external edge where the second
stage of Astacus has plumose setae.

The second antenna (fig. 77) has greatly grown in length and in perfection
of form and as above noted (fig. 69) is no longer carried in the remarkable
position it occupied in the first stage (fig. 50). Yet while in a position to be of
use as a sense organ the antenna is still markedly lacking in setae : the exopodite
scale bears only a row of few spines and the long endopodite bears but a few
acicular setae toward its tip. With its increase in length there has been also an
increase in number of segments in the filament which has now 36 beyond the
three large basal segments in place of the 22 of the first larva.

The mandible (fig. 78) has added a row of small acicular setee along the
medial face of the end segment of the palpus, and developed sharp teeth along
the heavy cutting edge of its base. When the palpus is folded down into the hol-
lowed face of the mandible two teeth are dorsal and five ventral to the tip of
the palpus.

The first maxilla (fig. 79) has changed but little, but its spines are longer
and sharper and it has developed a few, minute, acicular setae.

This stationary state is still more pronounced in the case of the second
maxilla (fig. 80), which has only grown sharp setae in place of the blunt termi-
nal spines. The changes in the first maxilliped are also the development of
setae in place of spines and the addition of a few setae (fig. 81).

56 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS

In this second maxilliped (fig. 82) this substitution and addition of setae is
more pronounced but there is a noticeable retrogression in the gill which is
more simple, no longer having any lateral filaments.

The third maxilliped (fig. 83) again, as compared with the first stage (fig.
60), has quite long acicular setae in place of blunt spines, and a few sparsely
plumose setse, noticeably a group at the tip of the exopodite. While the pos-
terior gill is longer the anterior is here also somewhat reduced.

The chela now used as before for clinging to the mother has its tips some-
what recurved (fig. 84), but they are much straighter than in the more firmly
fixed first stage (fig. 61). There are added a few acicular setae and the claw
is more like the adult in the development of rasp-like spines along its edges
in place of the simple spines of the first stage which, as seen in figure 62, were
being replaced during the first stage by the toothed spines of the second stage.

The four walking legs (figs. 85, 86, 87, 88) have changed chiefly in the ad-
dition of a few terminal setae and of a few exopodite, thread-like setae.

The branchial formula is thus the same in the second as in the first stage.

On the abdomen the four functional pairs of pleopods (fig. 89) are now long
and slender but very simple and not yet fringed with setae, though the spinules
on the edges of the exopodite and endopodite are more numerous than in the
first stage.

The appendages of the first abdominal somite exist as yet only in the form
of minute round knobs (fig. 4; Andrews, :06), but slightly larger than in the first
stage. The appendages of the sixth somite are still within the telson (fig. 71).
When the larva is nearly ready to moult into a third stage these pleopods make
the telson protrude laterally more than in the above figure through the sub-
stance of the telson, allowing one to see the form both of the pleopods and their
setae. When they are expanded, at moulting into the third stage, these pleopods
have the appearance shown in figure 90.

The second larva remained fastened to the mother for six days, appar-
ently eating nothing, and as the yolk-mass gradually diminished it seems
probable that the larva still subsisted upon the original supply of energy
taken from the ovary as yolk. Before the moult into the third stage the gas-
troliths became quite conspicuous as blue areas showing through the body on
each side of the stomach.

The actual moult occupied but a few minutes and as usual the head-thorax
came out of the old shell first, then the legs were withdrawn from their cases and
finally a few flaps of the abdomen freed the larva completely. There being no
telson or anal thread this time, the larva at once left its old cuticle and climbed
upon the pleopod of the mother. The increased strength and size of the larva
with the perfection of its limbs and caudal-fan would make the danger of being
lost on falling away from the egg much less than it was in the preceding stages

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 57

as the larva was now well able to follow its strong instinct to crawl upward
and so recover its position on the mother, or, failing that, to live independ-
ently, as it soon did.

In the following description of the third larva we will emphasize its man-
ner of association with the parent.

In general form the young crayfish in this third stage (figs. 90, 91) is now
for the first time like the adult, yet the great size of the eyes and of the ex-
opodite scales of the antennae together with the very wide expanse of the tail
fan and its long swimming plumes give the larva the aspect of a pelagic larva
or of the adult of some lower form of marine decapod. In fact the ability to
swim freely in great leaps which the third larva soon exercises and the trans-
lucency of the body together with the big eyes and long antennae and very
slender long legs and chelae make the larva seem much like a small shrimp.

The rostrum is now directed straight forward and is armed with large
lateral spines that exaggerate the gothic style of the adult. All the appendages
are now provided with long setae which make them sparsely hirsute as seen
under the microscope, but only on the exopodite scale of the antenna and upon
the telson and sixth pleopods are the setae set in rows that suggest a locomotor
function. The use of the row of plumes on the scale of the antenna is not
obvious but the long plumes all along the edge of the telson fan seem to add to
its area effective in locomotion.

The animal was still translucent and within it the liver showed as a narrow
green band external to the large mandibular muscle, extending forward a short
distance and backward nearly to meet its fellow in the region of the heart.

The sixth pleopods were now no longer inside the telson and the telson
had become specialized as in the adult into an anterior and posterior part
separated by a distinct movable hinge. Through the clear dorral exoskeleton
was seen the anus and a large mass of muscle on each side in the anterior
region and in the posterior part of the telson the old radiating glands, which
had eventually perfected the long setae that a high power showed to be plumose.

The pigment cells represented by dark dots in figures 90 and 91, had be-
come more numerous than before but were still chiefly arborescent red cells,
though in many regions there were large blue cells not represented in the above
figures though they now altered the ground tone of the animals. Posterior to
the eyes the crowded pigment cells formed a streak along the base of the lateral
spines and more to the rear a rounded area over the attachment of the great
mandibular muscle. This round ai'ea on each side was especially conspicuous
from the dense crowding there of blue pigment mixed with red. The dark
aggregation of pigment cells across the anterior edge of the abdomen still re-
mained. The yolk area and its color were quite gone and on each side of
the stomach a blue area indicated the gastrolith. Owing to the fineness of the

58 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS

network of pigment cells on the tips of the chelae these areas appear conspic-
uously dark red.

While the young in the third stage still remained on the mother for a while,
they were free to move about and soon became more and more independent. A
few hours after moulting some of the young were found walking about on the
bottom of the aquarium. When disturbed they leaped backward and. upward
several inches by strong strokes of the abdomen and looked not unlike shrimp,
while, when they walked, their habit of holding the anterior part of the body
high up in the water as well as the attitude of the slender chelae gave them
the alert, nervous look of shrimp-like creatures and made them look very unlike
the adult.

The young climbed about on the pleopods of the mother, over her side and
back, upon her mouth parts and eyes and, though at first densely crowded under
the abdomen of the mother, more and more frequently they walked off to
greater distances, always returning to the abdomen if possible. The same
larvae that at times left the mother in the water, clung fast to her when she
was lifted out of the water. But by violently shaking the mother in the water
all the young could be shaken off. When two days after moulting into the third
stage some sixty larvas were thus shaken off and left in the same dish with her
all but twelve had returned to the mother's pleopods in twenty minutes. As
many as a hundred young were seen walking about the aquarium and climbing
up onto water plants for a time and later all but a few had returned to the
mother.

At first, however, the young did not wander far from the mother and when
in a darkened aquarium the mother stayed in one spot for two hours the small
faecal casts of the young over the bottom of the aquarium were almost all very
near to the mother.

In about a week this association of mother and offspring was gradually
given up and more and more of the young failed to return to the mother.

In nature it is possible that the mother and young separate quite soon,
especially if the mother wanders about, but as yet nothing is known of the
natural life of this crayfish when carrying the young. It may be that the
female then lives in holes or cavities and then the young might long remain
with her. In captivity the females with eggs will dig holes in, the mud and live
in them as long as the water is well aerated, but come out when the water is
"not running. When kept in a small dish the female had no chance to escape
from the young and in some cases some of the young remained with the mother
and crawled over her three weeks and three days after leaving the egg, but
when such females were put into a large tank they walked away and hid them-
selves, leaving the young scattered about.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 59

Possibly the restricted artificial conditions both prolonged the duration of
association of mother and young and lessened the variety of external stimuli
so that there was a certain amount of domestication. By close confinement
and by supply of abundant food to be given the mother and. young without
effort on their part, it would appear possible to make of the crayfish a domes-
ticated animal with a more prolonged association of mother and offspring. Such
experiments would build upon the ground that the crayfish is preeminently a
creature in which embryonic life has been continued on as a series of stages,
ancestrally free, but now dependent upon the mother and with special organs to
ensure that dependence.

The young that came down from the pleopods took food and eagerly de-
voured fragments let loose from the mouth parts of the mother when she was
feeding. At such times the young climbing on the mouth parts of the mother
seemed in danger from those rapidly vibrating appendages but always seemed
to be shoved aside and not devoured. When a couple of tubifex were put into
the water and seized by a female, the young also took hold and either car-
ried off pieces or continued to hold on while the worm was being dragged into
the mouth of the female. Thus the young were drawn up with the food to the
mouth of the female, but when between the maxillipeds the young leaped away
and none seemed to be injured.

The accompanying illustrations (figs. 92 and 93), being from photographs
of living crayfish in water but poorly represent the pinkish mass of active
larvje crowding under the abdomen of the mother or the separate young climb-
ing over the back of the mother or walking about in the dish. They serve, how-
ever, to show the crouching attitude of the mother, the size of the young in this
third stage and the general character of this active dependence of young upon
mother which was long since admired by Roesel von Rosenhof (1775), and might
be likened to the clustering of hen and chicks or of sow and pigs. Roesel von
Rosenhof 's statements regarding the association of the young and parent As-
tacus are as follows :

"Wenn die Mutter dieser kleinen Krebse, nachdem selbige sich zu bewegen
angefangen, zuweilen bei ihrem Futter stille, oder sonst ruhig sitzet, so be-
geben sich solche von ihr etwas weg und Kriechen urn zie herum; merken sie
aber nur im geringsten etwas feindliches, oder sonst eine ungewonliche Bewe-
gung im Wasser, so scheinet es, als ob sie die Mutter, sich zuruck zu begeben,
durch ein Zeichen erinnerte; indem sie allezusammen geschwind unter den
Schwanz zuruck fahren, und sich wieder auf einen Klumpen zusamensetzen,
worauf sich die Mutter sammt selbigen mit mogligster Eilfortigkeit, in Sicher-
heit begiebt, welche sie aber etliche Tage darauf , nach und nach verlassen. ' '

The suggestion of a possible signal to recall the young raises the question
as to the nature of the means by which the young associate with the parent.

60 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

The interrelation of mother and young in the crayfish would seem a profit-
able field for study of comparative family life and the following few facts sug-
gest lines of inquiry.

It is not evident that the mother gets any advantage from the clinging of
the young to her body, though if in the third stage they eat off the old egg stalks
and cases, the cleansing of the pleopods so caused might satisfy in the mother
something akin to whatever it may be that causes her to laboriously cleanse that
region just before the eggs are laid; but judging from the long endurance
of the load of eggs and larvae and from the frequency of dirt and parasites
upon the pleopods it seems hardly probable that the female would feel an in-
stinct gratified when the pleopods are clean again. That the female is at all
conscious of the presence of the larvae remains to be found out by evidence not
yet at hand; however, when a lot of young were put into a dish with a male
and they climbed over him he cleaned them off from his abdomen and seemed
to be annoyed by their climbing over his head, but when the same young were
put with a large female that had reared her own young long enough and natur-
ally separated from them some weeks before, they climbed up onto her withoiit
her showing any evident sign of being affected by their presence upon her
chelae, thorax and abdomen. When a female was feeding and the young climbed
upon her chelae she did not seem aware of them but reacted eagerly to a tubifex
near her chelae. Whether, then, the young are simply tolerated, [as are the
small parasitic leeches over the body of crayfish,] as a continuation of the eggs
that are part of the body, or whether the females have special responses
to stimuli given by the young is not known, but the former seems not improb-
able.

The young, on the other hand, act as if they were strongly affected by the
mother but this may be due to a few simple reflexes and without any complex

•

visual or other conception of the mother's existence. At all events there is
no evidence that the young distinguish one female from another and when two
mothers were in the same dish some young of one climbed up onto the other.
Even when the young shaken off a female when they were in the third stage
were put in a dish with a female carrying her young in the second stage they
climbed up amongst the younger larvae of the strange female and seemed con-
tent. When the young were shaken off two females in separate dishes and the
females exchanged, the young climbed up onto the strange females ; in a few min-
utes all but three were upon one female and all but seven or eight upon the other
though she was moving about. Some young C. affinis in the second stage were
taken off from the mother and put with some young of C. Diogenes of the sec-
ond stage also removed from the mother and all were then put into a dish with
another female C. Diogenes bearing young in the second stage. All the young
got upon the foster mother and continued there, though the C. affinis were

THE YOUNG OF THE CRAYFISHES ASTACVS AND CAMBARUS 61

scarcely more than one-half the length of the other larvae. The young that are
shaken off dart, swimming, about in the water but soon settle to the bottom and
climb up upon one another in heaps or try to climb up at the corners of the
dish and upon water plants.

The tendency to climb onto the mother is very strong so that when a
female walks along swinging her pleopods laden with young she often gathers
up free young that are walking about, as these when touched by a pleopod
may not spring away but turn and climb onto the mass. In fact early in the
third stage a larva that fell to the bottom, apparently for the first time, stood
with head end elevated and quickly responded to the presence of a passing
pleopod. Even if lying upon their backs they quickly seize and mount the pleo-
pod of a passing female. A piece of white cheese-cloth, however, did not appear
to stimulate them to climb upon it and when a lump of rough cement, a model
of a toad, was left in the aquarium very few got on it, most of them preferring
the mother.

Possibly the young receive chemical stimulus from the mother that aids
them in returning to her. That they responded to some chemical stimuli is
most probable and the following facts may be interpreted on this basis. When
the mother feeds, the young gather under her mouth and even after the food
is gone they remain as if excited by chemical substances coming from the
mouth parts of the female. It was also found that while the young climb onto
a dead female and even over the exposed surface of the freshly broken abdo-
men, after some days they remain on the rest of the surface but not upon the
broken surface where chemical substances due to decay probably existed.

During the time the larva? in the third stage associate with the parent the
large collections of old egg shells and skins on the pleopods disappear and
are probably eaten up by the larvae since their intestines contain minute setae
that might come from their old cuticle and since in Astacus, Chantran ('71)
foimd that the larvae eat their shells and cast off cuticles. It is therefore possible
that one reason the young remain with the mother is that this food supply on
the abdomen acts as a stimulus to them.

However, along with whatever chemotactic movements there may be, there
are other factors concerned in the association of the young with the female as
indicated by the few following experiments, which tend to show that the
young are controlled in part by responses to light and to gravitation and con-
tact. Thus when a small paste-board table was put under the water the young
collected on the under side of the horizontal paste-board and remained stand-
ing upon it, in an inverted position. When the paste-board was then turned up-
side down the young scattered in a few minutes so that half were off the paste-
board and some were under it in its new position. In crawling under such a table
the young reared up and seemed to be trying to reach it above their heads as if

62 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAEUS

influenced by it before they touched it. When a small glass table was used the
young also collected under it and reached up as if trying to climb up to it.
When dark paste-board was laid on part of the glass, above, twenty-two larvae
had collected under that part of the table shaded by the paste-board, in two
hours, and none under the clear part.

It may be imagined from these indications that the larvae in the third stage
have a tendency to climb upward due to negative geotactic responses, that they
prefer the shade as being photophobic and that they come to rest standing upon
a solid object as being thigmotactic. Assuming some such responses together
with some chemo tactic phenomena, possibly all the habits of the young in refer-
ence to the mother may be explained; possibly not.

The association of the young and the mother, however brought about,
endures in Cambarus affinis during two larval stages and a part of a third. In
Astacus leniusculus, however, it is the second and not the third stage which
gives up the association with the mother. Whether this is a generic difference
cannot be determined without extensive observations, as almost no data are yet
at hand. That Cambarus in general have three dependent stages seems prob-
able from the following few facts that have been recorded.

Faxon ('85) saw specimens of C. Clarkii 7 mm. long upon the abdomen of
the mother (as previously recorded by Hagen, '70), in which the tail-fan was
perfect so that with the ability to lead a free existence there was still the habit of
associating with the mother. In C. affinis larvas in the first stage are 4 mm., in
the second 5 mm., and in the third 7-8 mm. long, and it seems probable that the
above recorded C. Clarkii were also in a third stage. The same author saw
upon the mother C. gracilis 9 mm. and C. Bartonii 10 mm. long, with perfect
tail fan. These two species may well have three stages of association as in C.
affinis. Also he records C. rusticus just hatched and 4 mm. long as being so
embryonic that we may assume they would remain with the mother as long as
C. affinis does. On the other hand Steele ( :02), who first observed the living
larvae of Cambarus associated with the mother, records C. gracilis 7 to 8 mm.
long with a bent rostrum as if in the first stage though so large. And in a more
detailed study of C. virilis she describes the first stage and then a second stage
nine days old with the tail fan complete and other features of the third stage
of C. affinis, but as she says the larva six days old could swim it seems prob-
able that in both these species as in C. affinis there are three stages in the
period of association, the second of which is easily overlooked.

There is then no obstacle to assuming that we may expect to find in Cam-
barus that the larvae remain with the mother through a first, a second and part
of a third larval stage and that in Astacus they remain through the first and
part of the second only.

YOUNG OF THE CRAYFISHES ASTACTJS AND CAMBARUS

The active third larvae becoming independent lived some eighteen days in
all before moulting again to pass into a fourth stage and these in turn were
followed through more stages till eventually adults were reared in the labor-
atory. Without describing the gradual changes of the early larva; to the details
of adult form we may now give a more complete record of the rates of growth
of young crayfish than has hitherto been possible as a number of new observa-
tions have been added to those previously published, Andrews ( :04), and certain
points as to the period of sexual maturity determined. We will give certain
facts as to the number of moults, as to the rate of growth, as to the develop-
ment of the external male organs, as to the ratio of the sexes and as to the ar-
rival of sexual maturity and the ability to breed in captivity.

Observations made upon the young of a single female which laid March 28,
1903, and whose eggs hatched May 18, 1903, gave the times of moulting and
rates of growth of the larvae represented in the following table :

Stages.

Dates.

Duration.

Size.

Increase.

Habit.

1st stage.

May 18-May 20

2 days

4 mm.

Attached to mother.

2d stage.

May 20-May 26

6 days

5 mm.

1 mm.

Attached to mother.

f Associated with mother for

3d stage.

May 26-June 13

18 days

8 mm.

3 mm.

about one week and then

( free.

4th stage.

June 13-July 1

17 days

12 mm.

4 mm.

Free.

5th stage.

July 1-Julv 6

5 days

15-18 mm.

3-6 mm.

Free.

Gth stage.

July 6-July 17

11 days

21 mm.

3-6 mm.

Free.

7th stage.

July 17- ?

?

29mm.

8 mm.

Free.

These same young were kept till October 6, 1903, without observation and
the eight survivors then measured as follows : 62, 55, 53, 49, 50, 45, 43, 41
mm. in length. The average is nearly 50 and as far as can be judged from the
above table such a large larva as that measuring 29 mm. in the seventh stage
would probably have passed through at least four or five moults to become the
large one 62 mm. long and smaller larvae would have required as many or
more moults if the increment was as large as in passing from the sixth to the
seventh stage ; but if the increase was the average for the above seven stages,
scarcely 4 mm., then at least six more moults may have taken place. Other
data show that the rate of growth is very different in individuals and in some
cases seemed to depend directly upon food supply so that the number of moults
during the first summer is probably not by any means constant but different
in individuals. However, we are sure that at least seven stages may be passed
through and probably eleven to thirteen larval stages may occur in the first sum-
mer of the creature's life outside the egg. Yet data given below show that the
larvae may remain but 20 mm. long in the fall, owing, probably, to insufficient
food arresting them when in the sixth stage.

64 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

After October there were no moults till the following warm season, the
lengths remaining constant during the winter. Just as the growth in the first
summer was restricted to the five months of May, June, July, August, and Sep-
tember, so in the second summer there was an increase of 25 mm. during that
time and though the moults were not observed there may well have been four
or five during this second summer. In a few exceptional cases a moult took
place in the early spring before May and a gain of 6 mm. was observed then.
After a second winter of no moults there followed a third summer of growth in
which a single observation showed that a specimen 70 mm. long December,
1902, was 76 mm. long July 1, 1903, an increase of 6 mm. probably due to one
moult. As this same individual increased to 90 mm. by October, 1903, it prob-
ably moulted two or three times or in all three or four times during this third
summer.

We thus have evidence for seven and probably as many as twelve moults
the first summer, four or five in the second summer, three or four in the third
summer, and in the fourth summer perhaps only one or two moults to judge
from a single case of 8 mm. increase.

Without reference to the number of moults, observations upon the amount
of growth of young crayfish hatched from eggs laid in the laboratory and kept
under various artificial conditions in the laboratory, were made and are re-
corded below as a substitute for data never yet obtained as to the rate of
growth of American crayfish in the open.

The following list gives the length in millimeters from tip of rostrum to end
of telson of 101 young hatched in May, kept in six different tanks in different
years and under somewhat different conditions and measured in October when
four months old.

I. 62, 53, 53, 49, 50, 45, 43, 41.

IT. 60, 59, 52, 52, 45, 39, 40, 33, 30, 22.

III. 41, 38, 24, 56, 32, 44, 43, 39, 39, 33, 35, 36, 32, 34, 30, 23, 30, 29, 27, 32.

IV. 47, 39, 33, 27, 20, 23, 31, 38, 30, 31, 28, 30, 35, 35, 35, 34, 36, 42, 46, 52, 46,
45, 46, 41, 39, 40, 36.

V. 43, 51, 41, 49, 43, 37, 38.

VI. 55, 43, 55, 48, 38, 50, 40, 40, 53, 46, 40, 42, 40, 43, 50, 45, 44, 48, 50, 49, 37,
57, 44, 45, 43, 46, 46, 36, 38, 38.

It is obvious that there was great individual difference in size attained in
the first four months of life both under different conditions and when kept in
apparently the same conditions, but of course subject to different chances of
food supply even in one tank.

The first group of eight survivors ranged from 41 to 62, with an average
of nearly 50.

The second group of 10 survivors ranged from 22 to 62 with an aver-
age of 43.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 65

The third group of 20 ranged from 23 to 56 with an average of 35.

The fourth group of 26 ranged from 20 to 47 with an average of 36.

The fifth group of only 7 ranged from 37 to 51 with an average of 43.

The sixth group of 30 ranged from 36 to 57 with an average of 45.

The large size of the crayfish in the first group was undoubtedly due to
greater care taken to feed them and the differences in other groups were prob-
ably due to differences in food supply and also in temperature.

Judging from the above 101 measurements the young four months old may
vary in length from 20 to 62 mm. but while the average of all was 41 mm. the
average of different experiments ranged from 35 to 50.

We may then expect this crayfish to be nearly two inches long in the autumn
of its first year of life.

Measurements made in the autumn and again in the next spring showed
that there was no growth from October to May, except in rare cases in which
a moult occurred in early spring. The crayfish thus started in their second
summer of life with a length of nearly two inches and were the same size
when twelve months old as when four months old.

The rate of growth in this second summer may be inferred from some few
measurements made in October upon crayfish reared from eggs laid in the
laboratory and measured then, when sixteen months old. Of five larvae measur-
ing May 26, 1904, 62, 55, 53, 50, 62 mm. the three survivors in October, 1904,
measured 75, 80, and 72 mm., an average of 76 mm. From the average, 58, of
the above five to the average 76 of the three survivors there was an increase
of 18 mm., or a gain of 30 per cent in length in this second summer. And
records showed that one of these larvae had grown from 62 to either 75 or to
82, that is added 13 or else 20 mm. to its length, or increased 21 per cent or
else 32 per cent.

Another group of young left three survivors of 56, 70, 75 mm., or on the
average 67 mm. when 16 months old to represent the seven which were 40-45 mm.
long when twelve months old; they had thus probably added 25 mm. or gained
more than 50 per cent in the second summer.

A third group of young, twenty in number, ranging from 23 to 56 mm.
when twelve months old, left only two survivors at sixteen months, which
measured 70 and 79 mm., or an average of 74 : there was thus an increase from
the average 35, of 39 mm. But records of the individuals showed that the few
survivors were probably 43 and 56 mm. long in the spring and had grown only
23 and 27 mm. in each case which would be an increase of 53 per cent and of 63
per cent.

The above few data indicate a growth in the second summer of sometimes
50 per cent of the length; that is a crayfish two inches long the end of the first
summer may be expected to be three inches long the end of the second summer,

66 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

when sixteen months old. But here again the individual differences are very
great.

In the second winter there was probably no growth; two crayfish 75 and
80 mm. long in October, 1904, were the same length in May, 1905, and, in gen-
eral, moulting during the early spring was rarely observed.

The only observation upon the growth of crayfish reared from the egg
and kept during the third summer was the following: two individuals 70 and
79 mm. long when twenty-four months old left one survivor 90 mm. long in
October, 1903, when 28 months old. It had thus increased either 11 or else
20 mm. in the third summer, that is, it added only 14 per cent or 20 per cent
to its length.

Probably then a crayfish may grow in the third summer from a length of
three inches to be somewhat short of four inches.

The one young crayfish kept during its third winter did not change but
measured 90 mm. in October, 1903, and the same again in May, 1904.

In its fourth summer this crayfish grew to a length of 98 mm. by October
but died then when three years and four months old, having grown but 8 mm.
or barely 9 per cent in this summer. This may indicate a great diminution in
rapidity of growth as the maximum size is approached so that the crayfish one
hundred and twenty millimeters long that are taken in the Potomac may well
be six or seven years old; but from one specimen we cannot say that the rate
is naturally lessened in the fourth year and a possible yearly increment of one
inch would make the large crayfish of five inches only four years old.

The age of Cambarus affinis would seem to be roughly determinable from
the formula A = L — V, where A = the age in years ending in May, L = the
length in inches and V= one, in conditions of maximum favorableness, but in
unfavorable conditions V may become zero and in very old large crayfish V
may be a negative quantity.

Soubeiran ('65) gave the length of Astacus in France as 50 mm., 70 mm.,
90 mm., 110 mm., 125 mm., in the first to fifth years inclusive, that is with an
annual increment of 20 mm., which, however, became less in the fifth year, so
that he could not tell the age of crayfish 160 mm. long nor of any very old ones
190 mm. long.

Compared with this Astacus, C. affinis starting as a much smaller egg
caught up in size in the first summer and for two years showed just about that
same increment of 20 mm. annually, but then probably began to grow with more
diminished speed than did the French Astacus.

The sexes of these young crayfish are early determined and in the third
larval stage the female shows the beginning of the annulus and the male the
external openings of the deferent ducts, as elsewhere described (Andrews, :06).
But the difference between the appendages of the first abdominal somite in

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 67

male and in female are first well seen in the fourth stage when the female still
bears minute tubercles and the male long papillag to represent the appendages of
this somite. From that time on to the autumn the distinctive characters of the
sexes become perfected so that the annulus of the female is much like that of
the old crayfish, and the first abdominal appendages, or stylets, of the male are
also much like those of the full grown crayfish. It is thus very easy to recog-
nize the sexes by external characters when they are four months old. The
actual length in millimeters of the male stylets in crayfish of four months is
given in the following table:

Length of body . . . 55 53 49 45 43 60 52 52 45 39 40 33 30
Length of 1st stylet . 9 9 9 8 7 10 9 9 7 6 6 5 4
Length of 2d stylet . 10 10 9 7 11 10 10 8 7 7 5 4

The second stylets are thus longer than the first and as much as 18 per
cent to 20 per cent of the length of the body so that the stylets are in about the
proportions they will be in larger crayfish since specimens 115 mm. long have
stylets 18 and 22 mm. long.

Some examinations of various catches of adult crayfish indicated that there
is no great disparity in number of males and females and though it is not
known whether one sex or the other is subject to greater mortality in early
larval life, the following observations tend to show that the sexes are about
equal when four months old so that it may be that the eggs are about equally
male and female. Observed at four months: of 26, there were 15 male and 11
female; of thirty, 11 were male and 19 female; of 7, 4 were male and 3
female; of 19, 10 male and 9 female; of 10, 8 male and 2 female; of 8,
5 male and 3 female. Of the entire 100, 53 were male and 47 female.
With no marked disparity in numbers and with well formed external
organs the two sexes when four months old and about two inches long often
have well developed sexual instincts. Thus in October a male 55 mm. long,
1 5 mm. wide, with tail fan 22 mm. wide, antennae 48 and 51 mm. long and entire
expanse from tip of chela? to end of telson only 75 mm., was seen to try to con-
jugate with a sister 62 mm. long when four months eighteen days old. An-
other female had a mass of sperm transferred to its annulus by a male of like
age when four months old and 57 mm. long. Many cases were seen in which
the four months young had conjugated, thus of 19 females four months old, in
one aquarium, five bore sperm given by males of like age. Though the sperm
transferred by these young males was apparently perfect it seemed doubtful
if these unions would lead to fertile eggs but when a number of four months
females thus provided with sperm by males of like age were kept isolated from
all males during the winter they laid eggs in the spring which developed and
thus demonstrated not only that the females could lay eggs when but a year

68 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARITS

old but also that these eggs would develop after union with males of the same
age, union which moreover took place in the previous autumn so that these ex-
periments also showed that the sperm got in the autumn and kept all winterwould
fertilize the eggs, parthenogenesis being, supposedly, out of the question. In
Astacus, Chantran stated that the eggs were laid only ten to forty-five days
after union but in Camlarus affinis as many as 230 days may elapse. The
data on which the conclusions rest are as follows. A crayfish 62 mm. long laid
eggs when forty-seven weeks old, and these eggs hatched eight days after ' the
mother's birthday; this female received sperm the preceding autumn from a
male of like age and after that was kept isolated. Three other females were
supplied with sperm in the autumn and laid eggs in the spring when one year
old and kept isolated from males. Another female 57 mm. long laid eggs May
26, 1904, when one year old, having hatched May 18, 1903, and after being kept
isolated after conjugation with a male of like age in the autumn of 1903. An-
other female only 50 mm. long laid eggs when about eleven months old, April
29, 1905.

It thus seems demonstrated that a crayfish growing the first summer to
the length of about two inches and receiving sperm from a male of like age
in the autumn may lay fertile eggs the next spring when scarcely a year old.

When older, 16 months old and about three inches long, that is in the sec-
ond autumn of their lives, crayfish were seen to conjugate and to lay fertile
eggs the following spring when two years old. In one case it was shown that
a female which laid eggs when 62 mm. long and not quite one year old again
laid eggs the next spring when 80 mm. long and but a few days over two years
of age.

Though it is possible that artificial conditions may have made these cray-
fish that reproduce when a year old precocious, it is probable that this Cam-
barus comes to sexual maturity much sooner than does the Astacus of Europe
of which both Soubeiran ('65) and Chantran ('70) state that it reproduces first
~in its fourth year, though the latter says the males were ready for conjugation
at the beginning of their third year.

The fact that one female Cambarus affinis laid in two successive years is in
contrast to the statement credited to Steffenberg ('72) that the female Astacus
in Sweden hiding away during the winter, if fecundated, breeds only every other
year.

It is finally to be noted that not only did the young of C. affinis reared in
captivity lay fertile eggs but the young of the next generation also, so that there
would seem to be no obstacle to the establishment of a permanent race of domes-
ticated crayfish bred in captivity.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAEUS 69

COMPARISONS AND CONCLUSIONS.

The chief differences between the young of Astacus leniusculus and those
of Cambarus affinis are to be found in the first and second stages and are dif-
ferences in size, in habit, and in structure.

The differences above described may be enumerated as follows. In Cam-
barus affinis the larva coming from a small egg about 1.75 mm. in diameter
is about 4 mm. long and lives only two days before moulting. In Astacus lenius-
culus the larva coming from a very large egg, 2.5 mm. in diameter, is about
9 mm. long and lives four or more days before moulting. The first larval stage
in Cambarus has a simplified telson not well armed but having only 26 spines
which are upon its posterior edge only, while the Astacus has 66 spines that are
set along the lateral as well as the posterior edges. The abdominal append-
ages differ in that the first pair are absent in Astacus while barely recogniz-
able in Cambarus and the four following have equal exopodites and endopodites
in Cambarus while in Astacus the exopodite is longer. The telson thread is
short in Cambarus and long in Astacus, and in Cambarus there seems no part of
it a recent cuticle cast off by the embryo with well developed limbs as is the case
in Astacus. The first antenna in Cambarus is more simple in having only four
in place of five segments in its exopodite and in its endopodite and in lacking
the sense-hair of Astacus. The second antenna in Cambarus has 25 segments
while Astacus has 50; moreover, Cambarus carries this antenna bent backward
close to the body between the legs while Astacus carries it forward, but de-
pressed. In Cambarus the first maxilla lacks the few plumose setae of Astacus
and has fewer spines; and the maxillipeds have fewer setae and spines, as well
as gills of more simple structure. The gill formula of Cambarus is already
that of the adult and is therefore more simple than that of Astacus, but besides
this generic difference the gills of Cambarus are more simple in structure, in
this first larval stage, in many cases, especially the anterior arthrobranchs of
the pereiopods.

In the second larval stage the habits of the two are different in that the
young Cambarus still remain inactively fixed upon the mother and are aided in
doing so by an anal thread, while the young of Astacus soon wander away from
the mother. The former are about 5 mm. long and live about six days before
moulting while the latter are 11 mm. long and live 8 to 10 days before moult-
ing. In Cambarus the rostrum is more bent and not so efficient as a protection
and the setae over the entire animal are much less developed. The abdomen of
Cambarus has only weak spines upon its telson and these are along its pos-
terior edge only, while in the active Astacus there is a complete fringe of long
plumose setae on all the edges of the telson. In Cambarus the first antenna
is less perfected ; in having only 5 segments in its exopodite and 4 in its endo-

70 THE YOUNG OF THE CBAYFISHES ASTACUS AND CAMBARUS

podite while Astacus lias G in each; in having but 5 sensory hairs in place
of 8 in Astacus which has advanced further as is shown by the arrangement of
these hairs, and in having the ear pit still bare while in Astacus it is guarded
by a fringe of plumose seta? along its edge. In Cambarus the second antenna
has 39 segments and its scale has a row of a few spines only while in Astacus
there are 54 segments and the scale is fringed with plumose seta;. In Cambarus
the maxillae and maxillipeds have but few setae and no plumose ones except on
the tip of the last maxilliped and the edge of the scaphognathite, while in Astacus
the plumes are conspicuous and show a tendency to extend out to the cutting
edges of the protopodites and to thus replace the simple setae by highly special-
ized forms of setae with lateral barbs. The scaphognathite in Cambarus is
more simple in lacking the peculiar long plume-like setae at its posterior end.
The chelae are used by Cambarus to hold fast to the mother and their tips are
somewhat less straight than in Astacus. In Cambarus also the remarkably long
exopoditic setae of Astacus are not developed.

The first two stages in which the larvae of these crayfish differ most are
also the stages in which crayfish are peculiar in having an intimate association
of larvae with parent. From the generally accepted standpoint that crayfish
have been evolved from marine ancestors which had pelagic, or at least, active
larva? that left the mother as soon as they were hatched, the association in the
crayfish is a new acquisition. The differences between the larvae are also pre-
sumably of recent origin since they make the early stages more unlike than
later stages, while if there were a common ancestor the greater divergence
would be in the most remote descendants and stages, until some newer change
modified the early larvae and thus "falsified" the record.

Some of the new modifications in structure that go along with the new
habits of association of larvae and mother may be recognized as distinct from
the small size and other characters that might belong to active larva?. The
characters in the first and second stages that seem inimical to free larval life
and to be adapted to the parasite-like life upon the mother are; partly those
negative traits which an embryo might have in protected sedentary life and
which here may be in fact but the lingering on outside the egg of conditions
formerly found only within the egg; and partly directly adapted additional
characters that are peculiar to this life of larval dependence upon the pleopods
of the mother, and of no use elsewhere.

The embryo-like characters of the first larval stage are as follows. The
spheroidal head-thorax and accompanying position of limbs and of abdomen
that make walking and true swimming impossible and force the creature to lie
upon its side if removed from its natural attachment to the mother. The weak,
imperfect state of the locomotor organs ; slender legs, simple telson, absence
of utilizable sixth pleopods. The lack of useful defensive organs, that is the

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 71

bending down of the rostrum between the eyes and the small number and insig-
nificance of the telson spines. The imperfect state of the sense organs ; namely
the short eye stalks and incomplete eyes, the open unguarded ear-pit, the com-
plete or nearly complete absence of sense set;c on the first antenna and the naked
character of the other appendages and whole body over which only a few simple
spines take the place of the innumerable sensory and locomotor setae of active
larval stages. The lack of development and of use of the first and sixth pairs
of abdominal appendages ; the imperfect development and shortness of the first
and second antenna;; the lack of teeth on the edge of the mandible and the ap-
parent lack of use of any of the numerous mouth parts and appendages con-
cerned in later stages in getting and eating food. The passive habit as a
fixed dependant with physiology like that in the embryo, except for the addi-
tion of active respiratory movements; the pose of the body with the limbs and
abdomen beneath the thorax and antennae depressed.

The special characters of the first larva that are neither embryonic nor
such as a free larva would have are the two means of attachment to the mother.
The first is the existence of recurved tips on the long strong chela? that, com-
bined with the instinct of the larva, enable it to seize hold of and become locked
to the material on the mother's pleopods. The second is the telson-thread that
holds the larva to the mother till it can get locked with its claws. This con-
trivance is formed in advance of its use both by early adhesions of membranes
and by later special secretions of telson glands so that its usefulness is depend-
ent upon a series of modifications of the ancestral history.

In brief the first larval stage is embryonic in proportions and activities and
in lack of the perfection of sensory, feeding, locomotor, and defensive organs to
be expected in a free larva. It is actively specialized for its peculiar associa-
tion with the parent by the locking claws and telson thread.

The second larval stage is transitional in structure from an embryonic to
a free larval state and in habit it remains still a fixed dependant in Cambarus
though in Astacus gradually becoming but loosely associated with the parent.
In both crayfish the second larva is still imperfect in lacking the sixth pleopods
and is embryonic in still containing yolk. It also has imperfections in sensory
and locomotor setae that may be interpreted as retrogressions from a more per-
fect ancestral state toward a yet more simple state like that of the first larva;
presumably the association with the mother was first acquired in the first stage
and has later extended, as yet, less thoroughly through the second stage.

Supposing the ancestors of crayfish to have hatched as active larva the first
and second stages at present are new, in so far as they are specialized for at-
tachment to the mother and in that they are inactive and imperfect, while the
third stage may be compared more directly with ancestral larvae and is older
in its general structure.

72 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

While the absence of the locomotor sixth pleopods in the first and second
stages of crayfish young might be regarded as indicating that these stages had
never been represented by free ancestral forms but were merely embryos prema-
turely removed from the egg to live a pseudo-larval life upon the mother's ple-
opods, yet the near marine relative of the crayfish, the lobster, likewise has no
available sixth pleopods in its first and second stages though free and even pel-
agic, and we are free to assume that the first stages of the crayfish are modified
representatives of free ancestral larvae.

Such ancestors may have been much like the lobster and at present the
third larval stage of the lobster is like the third in the crayfish in that the
sixth pleopods are then first expanded; but it is not till the fourth larval stage
in the lobster that the length of antennae and perfection of tail-fan is developed
enough to be comparable to the third stage in the crayfish. While the first and
second stages of the crayfish are well adjusted to life upon the mother's ple-
opods, the first, second, and third stages of the lobster are well fitted for pelagic
life in retaining the locomotor exopodite of the pereiopods and short antennae.
The fourth stage of the lobster first acquires long antennae, perfect tail fan and
reduced exopodites, and is in the main very like the third stage of the crayfish ;
in fact the adult state is rather suddenly imitated in the third stage of the cray-
fish and in the fourth stage of the lobster. If these two stages are supposed
to be homologous we may suppose that the process of reduction of metamor-
phoses that has already gone so far in the lobster (Herrick, '95), has advanced
a little more in the crayfish so that only two larval stages exist where there used
to be three.

The greater length of the antennae in the earlier stages of the crayfish and
the earlier presence of the 2nd-5th pleopods may be imagined as secondary
changes from the lobster-like state, possibly connected with development of
crawling habits and abandonment of pelagic life, for the long antennae would be
of more use to a creeping animal and the pleopods perhaps of more use in con-
nection with respiration and sensory examination of water to an animal liv-
ing on the bottom, or possibly in holes, and needing a supply of water to the gill
region and information of the nature of the material beneath the abdomen.

In the departure of crayfish from marine lobster-like ancestors the changes
have been in the abolition of most of the free swimming contrivances, the ac-
quisition of some arrangements better fitted for a crawling life and finally the
retention of embryonic states along with special new adjustments in connec-
tion with a life of quasi-parasitism upon the mother.

We imagine the ancestral crayfish to have given up pelagic larvae, to have
developed crawling larvae, and with these to have lately begun an association
of larva and parent that forms an early phase in family life. If continued in
the same lines there might ultimately result a crowding back of hatching nearer

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 73

to the time of egg laying and a retention of embryo-like larvae upon the mother
along with reduction in number of larval stages, that would allow for a long
family life and protection of young nearly to the adult state.

That Cainbarus has departed from the ancestral state more than has Asta-
cus is shown by the following considerations. In C. affinis the telson is more
reduced, that is its shape is less like that of an ancestral swimming organ and
its protecting spines are only upon the posterior edge and not along the side as
well, and, moreover, there are but 32 as compared with 66 in A. leniusculus or,
probably, 50 in one Astacus of Europe. Cambarus affinis holds its second an-
tennae bent back under the thorax out of the way of jostling neighbors upon
the pleopods but in a position of no use as a feeling organ. This antenna is
also veiy short and has but 25 segments as against 50 in Astacus. In Cambarus
the appendages of the first abdominal segment, which will ultimately be sexual
organs in the male, are started in the first stage though lacking till much later
in Astacus, as far as known. And the young develop to sexual maturity within
four months, thus shortening the period of non-sexual life remarkably. Rathke
('29) found no signs of stylets in male Astacus 1 inch 3-4 lines long while we
find them 0.1 mm. long in C. affinis 17 mm. in length. The telson thread of
Cambarus seems made less evidently from a recent larval skin and is apparently
of earlier origin than in Astacus, as it seems to arise further back in the em-
bryonic life; or we should say the larval history of Astacus is the more primitive
in having a more complete representation of a lost larval stage still evident in
a complete cast cuticle within the egg. But while there is a cuticle cast off near
the time of hatching in both Astacus and the lobster we may assume from com-
parison of these larv;e that the first stage of the lobster is represented within
the egg of the crayfish and that therefore the cuticles cast at hatching are not
homologous.

In the second stage of Cambarus there are also signs of further recession
from ancestral states. Thus the rostrum is less developed and not as efficient
as a defense as it is in the more active Astacus. The second larva of Cam-
barus still lacks most of the plumose setae that are present in the second As-
tacus and is thereby less fit for free life and is also more like an embryo. The
second stage of Cainbarus lives upon the mother while in Astacus it becomes
free : in Cainbarus it is fast by its chelae and when it moults a delay in casting
off the cuticular lining of the intestine makes an anal thread that mechanically
continues the attachment of the young to the mother beyond what is found in
Astacus. The telson of Cambarus affinis, even in the second stage, has only spines
in place of the locomotor plumes of Astacus and is thus evidently unfit for free
life. Cambarus also has not yet developed sense setae upon the second segment
of the exopodite of the second antenna and is thus not as advanced as Astacus
is ; and the ear pit is less perfected in not having the setae along its edge. The

a

74 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS

second antenna is less perfect in having only 39 in place of 54 segments and iu
still having only spines in place of plumes upon its scale. In Cambarus also
the second stage is notably lacking in almost all plumose setae and is thus
further removed from fitness for free active life.

The third stage of Cambarus though rivaling Astacus in perfection of loco-
motor and sensory apparatus still associates longer with the mother and thus
suggests a future period when the larval dependence may be extended so that
more than two larval stages may remain upon the mother.

Though the young of Cambarus are better fitted to stay with the mother,
and do so for a longer period of their life as reckoned in stages, the actual
number of days in which the association continues is not essentially different in
Cambarus and in Astacus. In the former the larvae is fixed on the mother for
a week and then remains in association for another week or more. In the latter
the larva is fixed to the mother four to fourteen days and then is associated for
only a few days more, as far as was made out in laboratory culture of A. len-
iusculus, while Chantran ( '70) states the young of a European species are fixed
for ten days and then go and come for ten days more.

The conclusion that Cambarus has advanced further than Astacus in the
adaptation of its young to a life of association with the mother is in harmony
with the relative positions of these two genera as determined by anatomy and
geographical distribution. The absence of the pleurobranchiae in Cambarus and
the presence of a specialized sperm receptacle, the so-called annulus ventralis,
as well as the corresponding specialization of the male stylets, are some of the
important characters that show the adult Cambarus to be more highly evolved
than Astacus, and Ortmann ( :02) has shown how the evolution of all the species
of Cambarus may have taken place since divergence from Astacus like ances-
tors in the region of Mexico.

We may therefore suppose that as Cambarus has migrated over the middle
and eastern United States it has become split up into the sixty odd species now
found and in some as in C. affinis has made more perfect the association of
young and parent already present in the Astacus ancestor.

As all the crayfish are primarily fresh water or land dwellers it is natural
to seek to connect their possession of an elementary family state with their de-
parture from their ancestral marine life and it is easy to imagine that the species
might be benefited by the young being protected by the mother when either liv-
ing in holes or moving from place to place till of larger size and more perfect
structure. But it is not obvious that the advantage would be greater in fresh
water than in salt water life, and as we know the lobster has already greatly
shortened its ancestral series of metamorphoses and that the crayfish family-
life is possible only after such shortening of metamorphoses, we seem, in the
lack of evidence as to when the association found in the crayfish really began,

THE YOUNG OP THE CRAYFISHES ASTACUS AND CAMBARUS 75

to have no grounds for connecting fresh-water life with these peculiarities of
crayfish. The marine ancestors of crayfish may have already acquired some con-
nection of young and parent before leaving the sea and in fact the life in bays
and estuaries would be one in which the dangers of loss of young if set free
early and swept out to sea, would make an attachment to the parent especially
valuable! And, later, the main advance of crayfish ancestors having been pre-
sumably up rivers and across country from river to river, the advantage of hav-
ing the young not set free early when they might more easily drift down
stream or be devoured, but when they were large enough and able to crawl and
to hold to the bottom, would perhaps lead to a continuance and perfection of
family life.

But while it is easy to speculate on the origin of the characters of cray-
fish on the assumption of utility and the working of natural selection, the con-
clusions are of doubtful value in our present relative ignorance of their actual
life. Moreover, the nature and the amount of differences in the hard parts and
in the larval history that distinguish one kind of crayfish from another are such
as to raise the question whether utility and natural selection have played any
part in their formation or in their perfection. All the specific and generic
characters of crayfish may be as useless as color differences, and they may have
suddenly arisen perfected as we see them, or they may have progressed in
certain lines for long periods of time independent of external agencies. We need
more evidence from observation and from breeding experiments before con-
cluding that such characters as the shape of stylets and annulus or of rostrum and
of spines, absence or presence of one gill filament more or less, or the behavior
of telson glands and the presence of feathered setae instead of simple spines,
have ever in any manner been connected with utility to the species or with the
survival or the extinction of individuals. Until the contrary is proven we may
regard these as the unmeaning by-products of unknown activities in the living
protoplasm.

76 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

LITERATURE.

ANDREWS, E. A. :

:04. Breeding Habits of Crayfish. Amer. Nat., vol. 38, pp. 165-206, 10 text figs.

:04'. Crayfish Spermatozoa. Anatomische Anzeiger. xxv, pp. 456-463, 7 figs.

:06. Ontogeny of the Annulus ventralis. Biol. Bull., vol. 10, pp. 122-137, 25 text figs.

:062. Egg-laying of Crayfish. Amer. Nat., xr., No. 473, pp. 343-356.

:063. Geographical Distribution of Crayfish. ,J. H. Univ. Circular, May, 1906, pp. 100-

103.
:064. The Future of the Crayfish Industry. Science, N. S., vol. xxm. No. 60, pp. 983-

986.
CHAN THAN :

'70. Observations sur 1'Histoire naturelle des fiorevisses. Compt. Rend. Acad. Sci. Paris,

vol. 71, pp. 42-45.
'71. Nouvelle observations sur le development des ficrevisses. Compt. Rend. Acad. Sci.

Paris, vol. 73, pp. 220-221.
FAXON, \V.:

'85. A revision of the Astacida;. Mem. Mus. Comp. Zool., vol. 10, no. 4, vi -+- 186 pp.,

10 pi.
HAGEN, H. A. :

'70. Illustrated Catalogue of the Museum of Comparative Zoology at Harvard College.
No. 3. Monograph of the North American Astacidae. Mem. Mus. Comp. Zoiil.,
vol. 2, no. 3, viii + 109 pp., ] 1 pis.
HKIIKICK, F. H. :

'95. The American Lobster. Bull. U. S. F. C., Washington, 252 pp., 54 pis.
HUXLEY, T. H.:

The Crayfish : An introduction to the study of zoology. New York, 8vo, xiv -f- 371

pp., illus.
OISTMANN, A. E. :

:02. The geographical distribution of fresh-water decapods and its hearing upon ancient

geography. Proc. Amer. Phil. Soc., vol. 41, pp. 267-400.
RATHKE, H. :

'29. IJeber die Bildung und Entwickclung des Flusskrebses. Leipzig, 97 pp., 5 pis.
REICHENBACH, H. :

'86. Studien zur Entwicklungsgeschicte des Flusskrebses. Frankfurt am Main. 137.

pp., 14 pis.
L'OESSEL VON ROSENHOF:

1755. Der Monatlich-heransgegebenen Insekten Belustigung. in, pp. 305-350, pis. LIV-

LIX. Nurnberg.
SOUBEIRAN, L. :

'65. Sur 1'Histoire naturelle et 1'Education des ficrevisses. Compt. Rend. Acad. Sci.

Paris, vol. 60, pp. 1249-1250.
STEELE, MARY:

:02. The Crayfish of Missouri. Publ. Univ. Cincinnati, Bull. 10, pp. 1-50, 10 pis.
STEFFENBERO :

'72. Bijdrag Til Kanne domen om flodkraftens natural historia. Abstract in Zool. Rec-
ord. IX.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 77

EXPLANATION OF PLATES.

All figures drawn with camera lucida with Zeiss lenses specified, with few exceptions noted.
They are printed one-third the diameter of the drawings, except Figs. 92 and 9.'$, which
are nearly life size.

ASTACUS LENFUSCULUS.
PLATE I.

Figure 1. Larva issuing from egg-shell. 290 mm., aa.

2. Pantograph enlargement of photograph of living female to show young, several

hours after hatching, crowded upon the under side of abdomen of mother.

3. Right side of living larva soon after hatching. 290 mm., aa.

4. Dorsal view of living larva just hatched, showing split egg-case and long filament

connecting it to telson of larva. 290 mm., aa.

5. Front and oblique side views of eyes and rostrum to show its curvature. 2. aa.
(i. Dorsal face of left antennule of first stage. 2. A.

7. Under face of left antenna of first stage. 2. A.

8. Outer face of left mandible of first stage. 2. A.

9. Outer face of first maxilla of first stage. 2. A.

10. Outer face of second maxilla of first stage. 2. A.

11. Outer face of first maxilliped of first stage. 2. A.
121. Outer face of second maxilliped of first stage. 2. A.

PLATE II.

Figure 1:1. Outer face of third maxilliped of first stage. 2. A.

14. Posterior face of left chela of first stage. 2. A.

15. Posterior face of left second walking leg, first stage. 2. A.

16. Posterior face of left third walking leg, first stage. 2. A.

17. Posterior face of left fourth walking leg, first stage. 2. A.
IS. Posterior face of left fifth walking leg, first stage. 2. A.
19. Anterior face of one of left pleopods of first stage. 2. A.

PLATE III.

Figure 20. Dorsal face of telson of first stage, showing internal radiations, marginal spines,
and attachment of telson thread. 2. A.

21. Enlarged views of attachment of telson-thread to certain glandular spines on the

posterior edge of the telson of first stage. 2. D.

22. Detail of three such glandular telson spines still covered by cuticle of embryo.

From a larva just hatched, but not yet shed. 4. D.

23. Dorsal view of living larva in second stage. 290 mm., aa.

24. Left side of living larva in second stage. 290 mm., aa.

25. Upper face of left antenmile of second stage. 2. A.

26. Under face of left antenna of second stage, with flagellum represented in two

isolated parts. 2. A.

1 In this and the sul>sequeiit live figures the anterior arthrobranch has l>een dotted for distinctness.

?8 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS

PLATE IV.

Figure 27. Outer face of left mandible of second stage. 2. A.

28. Inner face of left mandible of second stage. 2. A.

29. Outer face of left first maxilla of second stage. 2. A.

30. Outer face of second maxilla of second stage. 2. A.

31. Outer face of first maxilliped of second stage. 2. A.

321. Outer face of left second maxilliped of second stage. 2. A.

33. Outer face of left third maxilliped of second stage. 2. A.

34. Posterior face of left chela of second stage. 2. A.

PLATE V.

Figure 35. Posterior face of left second walking leg, second stage. 2. A.

36. Posterior face of left third walking leg, second stage. 2. A.

37. Posterior face of left fourth walking leg, second stage. 2. A.

38. Posterior face of left fifth walking leg and pleuro branch. 2. A.

39. Posterior face of a left pleopod of second stage. 2. A.

PLATE VI.

Figure 40. Dorsal aspect of living larva in the third stage in normal attitude which makes
the telsou fore-shortened. 290 mm., aa.

41. Side view of living third-stage larva kept quiet by alcohol. 290 mm., aa.

42. Dorsal aspect of the left newly expanded pleopod of the sixth segment of the

third-stage larva. 2. A.

43. Dorsal aspect of the tclson of third-stage larva. 2. A.

CAMBARUS AFFINIS.
PLATE VII.

Figure 44. Posterior face of fourth left pleopod of adult female. 290 mm., aa.

45. Eggs attached to pleopod of adult female about twenty hours after being laid.

290 mm., aa.

4(5. Ventral aspect of posterior part of abdomen of first larva, showing attachment
of telson thread, the concealed sixth and free fifth and fourth pleopods. From
a recently hatched larva. 2. A.

47. Dorsal aspect of telson and sixth abdominal somite of first larva twenty hours

after hatching. 2. A.

48. Ventral aspect of terminal middle part of tekon of first larva dissected out of

egg-shell, showing attachment of telson thread to certain spines. 2. D.

49. Dorsal aspect of first larva as seen in Worcester's liquid. 290 mm., aa.

50. Right side of first larva, seen in Worcester's liquid. 290 mm., aa.

51. Front view of eyes and rostrum of first larva, seen in Worcester's liquid. 2. aa.

52. Pleopod covered by larvae in the first stage and 48 hours old; alive; some few re-

moved. Camera lucida on dissecting stand, Steinheil Aplanatic, No. 9.

53. Dorsal aspect of left antennule of first stage. 2. A.

54. Lower face of left antenna of first stage. 2. A.

55. Outer face of left mandible of first stage. 2. A.

56. Outer face of left first maxilla of first stage. 2. A.

57. Outer face of left second maxilla of first stage. 2. A.

1 In Figs. 32 to 37 the anterior arthrobranch is dotted for distinctness.

THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 79

Figure 58. Outer face of left first maxilliped of first stage. 2. A.

59. Outer face of left second maxilliped of first stage. 2. A.

60. Outer face of left third maxilliped of first stage. 2. A.

PLATE VIII.

Figure 61. Posterior face of left chela of first stage. 2. A.

62. End of chela of first stage, showing new cuticle and spines within old. 2. D.

63. Posterior face of left second walking leg of first stage. 2. A.

64. Posterior face of left third walking leg of first stage. 2. A.

65. Posterior face of left fourth walking leg of first stage. 2. A.

66. Posterior face of left fifth walking leg of first stage. 2. A.

67. Posterior face of left pleopod of first stage. 2. A.

68. Dorsal aspect of second larva, in Worcester's liquid. 290 mm., A.

69. Left side of second larva, living, copied from Andrews, :04.

70. Part of pleopod with some young in second stage left upon it. Drawn living,

with dissecting stand and Steinheil Aplanatic, No. 9.

71. Ventral aspect of telson of second stage with included sixth pleopods and anal

thread issuing from anus; living. 2. A.

72. Ventral view of right half of telson of second stage to show marginal papillae.

2. D.

73. Telson and part of intestine removed, with attached anal thread and portion of

cast shell, ventral views. In A normal relation is shown; in B the puckering
of the intestine when the cast telson shell is pulled away from the telson. 290
mm., A.

74. Portion of intestines and chitinous lining, made transparent to show the limit of

the cast-off lining (y) and the region (.<•) where still attached. 2. D.

76. Dorsal aspect of left antennule of second stage. 2. A.

77. Under face of left antenna of second larva. 2. A.

PLATE IX.

Figure 78. Outer face of left mandible of second larva. 2. A.

79. Outer face of left first maxilla of second larva. 2. A.

80. Outer face of left second maxilla of second larva. 2. A.

81. Outer face of left first maxilliped of second larva. 2. A.

82. Outer face of left second maxilliped of second larva. 2. A.

83. Outer face of left third maxilliped of second stage. 2. A.

84. Posterior face of left chela of second stage. 3. A.

85. Posterior face of left second walking leg, second stage. 2. A.

86. Posterior face of left third walking leg, second stage. 2. A.

87. Posterior face of left fourth walking leg. 2. A.

88. Posterior face of left fifth walking leg, second stage. 2. A.

89. Posterior face of left pleopod of second stage. 2. A.

90. Dorsal aspect of living larva in third stage. 290 mm., aa.

91. Left side of living larva in third stage, reduced i/> from 2 aa.

PLATK X.

Figure 92. Photograph of side view of adult female and its young in third stage climbing

under and about the body.

9,'!. Pbotograph of dorsal side of adult female, with its young in third stage climbing
over its back.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE -ANDREWS

PLATE 1

ASTACUS LENIUSCULUS: FIRST STAGE
E. A. ANDREWS, del.

SMITHSONIAN CONTRIBUTIONS' TO KNOWLEDGE-ANDREWS

PLATE II

ASTACUS LENIUSCULUS: FIRST STAGE
E. A. ANDREWS, del.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE— ANDREWS

ASTACUS LENIUSCULUS: SECOND STAGE
V.. A. ANDREWS, At].

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE— ANDREWS

PLATE IV

29

ASTACUS LENIUSCULUS: SECOND STAGE
E. A. ANDREWS, del.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE— ANDREWS

PLATE V

ASTACUS LENIUSCULUS: SECOND STAGE
E. A. Annmtws, del.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE— ANDREWS

PLATE VI

ASTACUS LENIUSCULUS! THIRD STAGE
E. A. ANDREWS, del.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE-ANDREWS
M V x / VJ

PLATE VII

49

OAMBARUS AFFINIS: FIRST STAGE
E. A. AHDMWS, del.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE— ANDREWS

PLATE VIM

CAMBARUS AFFINIS: FIRST AND SECOND STAGES
E. A. ANDREWS, del.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE- ANDREWS

PLATE IX

83

CAMBARUS AFFINIS: SECOND AND THIRD STAGES
E. A. ANDREWS, del.

SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE- ANDREWS

FIGURE 92

FIGURE 93

CAMBARUS AFFINIS: THIRD STAGE
K. A. ANDREWS, photo.

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