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NATIONAL ACADEMY OF SCIENCES.

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FOURTH MEMOIR.

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‘

THE EMBRYOLOGY AND METAMORPHOSIS OF THE MACROURA.

W.. K. BROOKS,
"PROFESSOR OF ANIMAL MORPHOLOGY IN THE JOHNS HOPKINS UNIVERSITY,

4

AND

1s i= HERRICK,

_ PROFESSOR OF BIOLOGY IN ADELBERT COLLEGE,

LATE FELLOW IN THE JOHNS» HOPKINS UNIVERSITY.
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ue Introduction. sure
‘Il. The life history of Stenopus hispidus.
Section 1. Natural history of Stenopus.
Section 2. Segmentation and the early stages.
~ Section 3. Metamorphosis of the larva.
Section 4, The adult. —
- Remarks.
_ List of species.
_ Literature of Stenopus.
by Sig The habits and metamorphosis of Gonodactylus chi-

ragra.
Section 1. The structure and habits of the adult.
Section 2. Metamorphosis. ~ .

uly. The metamorphosis of Alpheus. _ p
Section 1. The metamorphosis of Alpheus minos.
Section 2. The metamorphosis of Alpheus hete-
rochelis iu the Bahama Islands.
_ Section 3. The metamorphosis of Alpheus hete-
rochelis at Beaufort, North Carolina,
Section 4. The metamorphosis of Alpheus hete-
rochelis at Key West, Florida.
_ Section 5. The larval development of Alpheus
sauleyi.

V. Alpheus: A study in the development of the Crus-
: tacea.
Introduction.
_ Methods.
‘Parr First.
Section 1. The habits and color variations of
Alpheus. >
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CONTENTS.

Part First—Continued.

Section 2. Variations i in Alpheus heterochelis.

Section 3. The abbreviated development of
Alpheus and its relation to the environment.

; Section 4. The adult.

Section 5, Variations from the specific type.

Section 6. Measurements.

Section 7. The causes and significance of varia-
tion in Alpheus sauleyi.

Part SECOND.

Development of Alpheus.
Section 1. Structure of the larva of Alpheus
sauleyi.
Section 2. The origin of ovarian eggs in _—
Homarus, and Palinurus,
Section 3. Segmentation in Alpheus minos.

Section 4. The embryology of Alpheus. Stages
1-13.

Section 5. Notes on the segmentation of Crusta-
cea.

Section 6. Cell degeneration:
Section 7. The origin and history of wenderas
cells in Alpheus.
Section 8. The development of the nervous sys-
tem.
Section 9, The eyes.
Section 10. Summary.
_ Section 11. References.
Explanation of figures (accompanying each plate).

[With fifty-seven plates. ]

323

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CHAPTER LI. “rstacg,
INTRODUCTION.

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By W. K. Brooks.

No great group of animals is more favorable than the Crustacea for the study of the history
and significance and origin of larval forms, for these animals possess a number of peculiarities
which serve to render the problem of their life history both unusually interesting and significant,
and at the same time unusually intelligible; nor are these peculiar features exhibited, to the

‘same degree, by any other great group of animals.

The body of an arthropod is completely covered, down to the tip of each microscopic hair,
by a continuous shell of excreted matter, and as this chitinous shell is not cellular it can not grow
by the interpolation of new cells, nor can it, like the excreted shell of a mollusk grow by the dep-
osition of new matter around its edges, for there are no such growing edges, except in a few
exceptional cases, such as the barnacles. Once formed and hardened the cuticle of an arthropod
admits no increase in size, and as soon as it is outgrown it must be discarded and replaced by a
new and larger one. The new shell is gradually excreted, in a soft condition, under the old one,
and as soon as this is thrown off the new one quickly becomes fully distended and solid. Asa
result, from the very nature of the chitinous shell and the method of renewal which its structure
entails, the growth of an arthropod, from infancy to the adult condition, takes place by a series of
well-marked steps or stages, each one characterized by the formation of a new cuticle and by a
sudden increase in size.

In most arthropods the newly-born young are very different in structare from the adults, and
growth is accompanied by metamorphosis. As the changes of structure are. necessarily confined
to the moulting periods, the stages of growth coincide with the stages of change in organization, and
there is none of the indefiniteness which often characterizes the different larval stages of animals
with a more continuous metamorphosis. On the contrary tlie nature of each change is as sharply
defined and as characteristic as the structure of the adult itself. As the moulting period is fre-
quently a time of inactivity the animal may then undergo profound changes without inconvenience,
and the successive stepsin the metamorphosis of an arthropod are not only well marked, but often
very profound as well.

In these features all the other arthropods are like the Crustavea, but another consideration,
the fact that, with few exceptions, the higher Crustacea are marine, renders the problem of their
life history nite more intelligible than that of any other class of animals.

So far as the ontogenetic history of the metamorphosis of a larva is a recapitulation of ances-
tral stages in the evolution of the species its retention at the present day must depend to a great
degree upon the persistency of those external conditions to which the larval stages were originally
adapted.

This is true at least of all free larvae, which have their own battle to fight and their own living

5 to get, and while a larva inside an egg or within a brood pouch may possibly recapitulate obsolete

ancestral stages, the survival of a free larva depends upon its adaptation to its present environ-
ment. :

As compared with the ocean the inorganic environment of terrestrial or fresh-water animals
is extremely variable, and changes in climate, elevation, and continental configuration are accom-
panied by corresponding changes in enemies, competitors, and food, so that the conditions which

325

326 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

surround a modern terrestrial larva must, in nearly every case, be very different from those under
which the remote ancestors of the species passed their life, but while this is also true, to some
degree. of marine animals their inorganic environment is comparatively stable, and the persistence
of so many ancient marine types shows that the changes in the organic surroundings of marine
animals take place much more slowly than corresponding changes on land. x

This fact, joined to the definite character of the changes which make up the life history of a
marine crustacean, renders these animals of exceptional value for the study of the laws of larval
development, and for the analysis of the effect of secondary adaptations, as distinguished from the
influence of ancestry ; for while Claus has clearly proved that adaptive larval forms are much
more common among the Decapods than had been supposed, his writings and those of Fritz Muller -
show that no other group of the animal kingdom presents an equal diversity of orders, families,
genera, and species in which the relation between ontogeny and phylogeny is so well displayed,
but, while proving this so clearly, Claus’ well known monograph also shows with equal clearness
that this ancestral history is by no means unmodified, and that the true significance of the
larval history of the higher Crustacea can be understood only after careful and minute and exhaus-
tive comparison and analysis.

Greatly impressed by this fact, I began nearly ten years ago to improve the opportunities
that were offered by the marine laboratory of the Johns Hopkins University, for obtaining more
complete and detailed knowledge of the larval stages of a number of Macroura, and this work has
been prosecuted at every opportunity up to the présent time. Some of my results have been pub-
lished in my monograph on Lucifer, in the Phil. Trans. Royal Soc. for 1882, and others are incor-
porated in my report on the Stomatopoda collected by H. M. 8. Challenger.

This memoir contains the life histories of a number of additional species based in part
upon my own studies at Beaufort, North Carolina, and at Green Turtle Key and New Providence
in the Bahama Islands, but chiefly upon the researches which one of my students, Mr. F. H. Her-
rick, has carried on under my general supervision. In 1886 he undertook, at my suggestion, the
study of the embryology and metamorphosis of the Macroura, and devoted three years to this sub-
ject under my direction, and the results which follow are almost entirely due to his zeal and
energy. He has completed the study of several subjects upon which I had previously made a
beginning, so that my own unfinished notes have been incorporated with his researches, and our
respective shares in the work are as follows: The chapter on Gonodactylus is entirely based upon
my own researches; the chapter entitled ‘‘ Alpheus, a study in the development of the Crustacea,”
is entirely the work of Mr. Herrick; the one on the metamorphosis of Alpheus is based upon our
combined studies, and that upon Stenopus is almost entirely the work of Mr. Herrick, as my own
contributions to this life history are of minor value except so far as they supplement his work.

I shall now give a brief outline or summary of the chief results which are described in detail
in each chapter. 3

>

THE LIFE HISTORY OF STENOPUS HISPIDUS.

During the six seasons which I spent at Beaufort, North Carolina, I captured in the tow-net,
at different times, some six or seven specimens of a remarkable pelagic crustacean larva, all of
them well-advanced and in nearly the same stage of development.

Nothing was learned of the earlier larval life nor of the adult form of the animal, although
enough was made out to show that it is one of the few Macroura which, like Peneus and the Ser-
gestid, have retained the primitive or ancestral metamorphosis, and that its secondary modifica-
tions are very slight as compared with those of ordinary macrouran larve, and also that the
Beaufort larvee are new to science. (See Pls. rx and x.)

These larve have the full number of adult somites and appendages, and in side view they are
very suggestive of the Sergestidz. They are very much larger than ordinary pelagic larve and
are quite different from any known forms of Macroura. :

The chief locomotor organs are the last pair of thoracic legs, which are extremely slender, as
long as the entire body of the larva, ending in flattened elliptical paddles, which are used as
sweeps for rowing through the water. They are stretched out in front of the body near the ~

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MEMOIRS OF THE NATIONAL AUADEMY OF SCIENCES. Byes

middle line and are then swept backwards and outwards, describing at each stroke a circle equal
in diameter to about twice the length of the body. By the vigorous use of these oars the larva
skims rapidly through the water, and its movements are not unlike those of a Gerris,upon the
surface of a fresh-water pond.

Notwithstanding the importance of a complete knowledge of the life history of the animal to
which this sergestid-like larva belongs, I was unable to complete the study at Beaufort, although
I made careful drawings of two stages and filed them away for future use.

Immediately upon our arrival at Green Turtle Key, in the Bahama Islands, early in June,
1886, our attention was at once attracted to a small, graceful, brilliantly colored prawn which was
found in abundance among the coral. (See Pl. v.) It proved to be Stenopus hispidus, a species
which is chiefly known to naturalists through specimens from the Indian and South Pacific oceans.
It has been recorded as occurring in the tropical Atlantic, but our knowledge of the adult has been
very scanty and imperfect, and nothing whatever has been known regarding its life history until
Mr. Herrick devoted himself to its thorough investigation.

It is an active, timid animal, and is one of the most brilliantly colored of the crustacea. As
it is also one of the most widely distributed, it 1s noteworthy that while its color markings are so
prominent and conspicuous they are extremely well fixed and constant; so much so that the speci-
mens from the Indian Ocean and the South Pacific agree with those from the West Indies down
to the most minute markings.

The adults are found in pairs, a male and a female swimming together side by side and exhib-
iting evidence of strong conjugal attachment to each other.

The most noteworthy fact in its history is its world-wide distribution, and the question whether
this can be a result of any peculiarity in its structure or habits at once suggests itself.

We should expect, on general principles, to find the least specialized species the most widely
diffused; and one which holds its ground in so many parts of the world, and without any change
of structure finds a safe and congenial home in seas so widely separated, might be expected to be
of indefinite or slightly specialized habits, but this is not the case. In structure, in habits, in color,
and in external appearance, and also in its metamorphosis, Stenopus is one of the most highly
specialized of the crustacea; and it owes its ability to survive in many seas to the accuracy and
delicacy of its adjustment to. a narrow range of conditions, rather than to indefinite aud vague
adaptation to many conditions. :

Its antennz are unusually long and slender, and the acuteness of its senses, togéther with its
very remarkable alertness; the quickness with which it perceives danger, and the rapidity with
which it escapes; have tndoubtedly aided it in holding its own wherever it has gained a foothold
in a suitable locality, and no crustacean, with the exception, possibly, of Gonodactylus chiagra, is
better adapted for life in a coral reef. P

It is well protected from enemies by a thorny armor of hooked spines, which cover all the
upper surface of its body and limbs, and as all the hooks point forward the attempt of an enemy
to swallow a Stenopus must be difficult and painful.

These facts no doubt account for its survival, and the length of its pelagic larval life is beyond
question an aid to its wide dispersal and to the discovery of new homes.

While we cannot state that the adult will not at some time be found upon the Atlantic coast of
our Southern States, there is no evidence that this is the case, and the larvee which were obtained
at Beaufort, North Carolina, were undoubtedly hatched from eggs which were carried upon the
abdominal appendages of parents in the West Indies or on the Florida Keys; and these larve
had therefore wandered more than six hundred miles from their birthplace. The species might
therefore be diffused through a chain of coral islands six hundred miles apart, from a single start-
ing point, in a very small number of generations.

The eggs, which are very small, are laid at night, and the segmentation, which Professor

Herrick has thoroughly studied by sections, is entirely confined to the nuclei, the yolk remaining

undivided ; Stenopus therefore presents a most pronounced type of centrolycethic segmentation.
The great mass of the egg consists of a homogeneous mass of yolk granules, which takes no

part in the process of segmentation and probably contains no protoplasm. This yolk is aggre-

gated around a central nucleus, which divides, probably indirectly, into two, four, eight, sixteen

398 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

nuclei, and so on until the number is yery great. As this process of division goes on the nuclei,
each with an investing layer of protoplasm, gradually migrate to the surface of the yolk, and at —
last form:a superficial investing layer around a central yolk, out of which all the protoplasm has
been withdrawn.

The yolk does not divide up into typical yolk pyramids, although the putlnes of the blasto-
meres are sharply indicated by transitory superficial furrows. :

The embryonic area is soon marked out as a region where the nuclei are densely crowded, and
the point of invagination is indicated by a solid ingrowth which penetrates the yolk to form the
inner layers of the embryo. The subsequent stages of embryonic development were not followed
in detail.

The larva hatches in the afternoon, and during the following night the parent moults and lays
another brood of eggs.

At the time of its escape the larva is a Protozoea, and its later history is of great interest, since
it unites features of resemblance to Lucifer, Sergestes, Peneus, and to the prawns in bonus with
individual peculiarities in which it differs from all of them.

At the time of hatching (Pl. vi and Pl. x1, Fig. 25) it has sessile eyes, ibcomsaies antenne,
an enormous mandible, a deeply forked telson, a long rostrum, and a complete series of append-
ages as far as the first pereiopods, which are essentially like the third maxillipeds. The long
hind body has no appendages and is only vaguely divided into somites.

Five or six hours after hatching it changes into a true zoea, much like that of an ordinar 'y
macrouran (Pl. vit). The carapace becomes much enlarged; the rostrum is shortened to less than
half its former length, the mandible becomes small, the forks disappear from the telson, the eyes —
become stalked, the antennz are shortened like those of a zoea, and the maxillipeds Beceane the
chief locomotor organs.

As these larve could not be reared in captivity the later stages were studied from captive
specimens, but Professor Herrick has proved that the Beaufort larve are either young Stenopi or
else the larvee of some closely allied species which is at present unknown.

A specimen a little older than the oldest Beaufort specimen was captured at Nassau (PI. X11).
It isin the Mastigopus stage, with greatly elongated eyes, and with antennx which are gradually
approximating to those of the adult. The third maxillipeds are now extremely long and are the
largest of all the limbs, while the huge, oar-like fifth pereiopod of the preceding stage is now
reduced to a rudimentary bud, and the fourth is also reduced to a two-jointed rudiment.

It thus appears that, as in the Sergestidie, the last two pairs of *‘ walking legs” are shed Atter
the Mysis stage, to be again reconstructed in the Mastigopus stage. After several moults the
Mastigopus larva gradually assumes the adult form, the principal changes: being the Sapp
of the eyes and the reacquisition of the fourth and fifth pereiopods.

ALPHEUS.

The genus Alpheus includes a large.number of small, brilliantly colored crayfish-like Cru-
stacea, which are widely distributed, although all are essentially tropical. Two species range
as far northward as the coast of Virginia, but the true home of the genus is the warm water
between tide-marks or near the shore in corai seas, and they occur in the greatest abundance
and variety in all the sounds and inlets among coral islands. They are well adapted, in structure
as well as in habits, for a life among the coral, and of all the Crustacea which abound upon the
coral reefs the genus Alpheus is one of the most common and most thoroughly characteristic (PI.
I, II, and Iv).

Nearly every mass of sponge or alge or of coral rock or living coral which is fished up from
the bottom and broken to pieces contains specimens of one or more species of Alpheus, and pieces
are often found which fairly swarm with these little animals.

A few of the species wander over the bottom, and wandering individuals of other species are
found occasionally, but their true home is in the tubes of sponges and the holes and crannies in —
the porous coral limestone, or under the broken shells and fragments of limestone which lie upon ~

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 329

-

the buttom in shallow water. Occasionally they inhabit short, vertical burrows, which they con
struct for themselves in the sandy mud, but most of the species pass their life hidden in the shelter
which they find upon the reef.

The most conspicuous characteristic of eh genus is the great enlargement of the claws of the
first pair of walking legs. Both claws are large, but one of them is enormous, and it serves as a
most formidable weapon of offense and defense. In some species this large claw nearly equals
the body in size, and it is usually carried stretched out in front of the body, but one species carries
it folded down under the body and hidden, ready to be instantly pushed out to make a rapid thrust
at any enemy.

In nearly all the species the large claw terminates in hard, powerful forceps. The claw or
dactyle is provided with a plug, which fits into a well or socket in the other joint and probably
serves to prevent dislocation. When the forceps are opened the dactyle is raised so that the plug
just rests in the mouth of the socket. As soon as the claw is released it is suddenly and violently
closed, as if by a spring, and the solid stony points striking together produce a sharp metallic
report, something like the click of a water hammer, and so much like the noise of breaking glass
_ that I have often, when awakened at night by the click of a little Alpheus less than an inch long,
hastened down to the laboratory in fear that a large aquarium had been broken. In the open
water the report is not so loud as it is when the animals are confined in small aquaria, but Al-
pheus is so abundant in all the Bahama Sounds that a constant fusilade is kept up at low water all
along the shore. The animals are remarkably pugnacious and they will even attack bathers. They
are known to the inhabitants of the out islands as “scorpions,” and are much dreaded, although
their attacks are harmless to man. The snapping propensity is exhibited both in the water and
out by both sexes, and if two males or two females, either of the same or different species, are
placed together in an aquarium, a most violent combat at once takes place, and quickly ends by’
the destruction of one or both. Some species appear to pinch with the large claw, but it is more
frequently used like a saber for cutting a slashing blow. The edge of the movable joint is sharp,
and rounded, and the animal advances warily to the attack with the claw widely opened and
stretghed out to its full length. Watching its opportunity it springs suddenly upon its enemy,
instantly closing its claw with a violent snap and a loud report, and cutting a vertical sweep with
its sharp edge. I have often seen Alpheus heterochelis cut another completely in two by a single
blow, and the victim is then quickly dismembered and literally torn to fragments.

The abundance of these animals in coral seas is well shown by the fact that of the twenty
species which are known to inhabit the shores of the North American continent we found twelve,
or more than half, upon a little reef at Dix Point, a few rods to the eastward of our laboratory at
New Providence, in the Bahama Islands. ~*

Of the thirteen species which we found in the islands several are new, and as none of them
have ever been adequately described, an illustrated, systematic description of all the species is
now in preparation by Mr. Herrick. The present memoir deals only with the embryology and
metamorphosis of the genus. This is a new field, for nothing whatever has as yet been published
upon the embryology of any species of the genus, and all our knowledge of the metamorphosis is
contained in two short abstracts without illustrations on the metamorphosis of a single species,
Alpheus heterochelis. Rggs have now been obtained from all thirteen of the Bahama species, and
the first larval stages of most of them have been reared from the eggs in aquaria in the laboratory,
and the metamorphosis has been traced from actual moults.

THE METAMORPHOSIS OF ALPHEUS.

One of the most remarkable results of our study of the various species of the genus Alpheus
is the discovery that, while there is such a general similarity as we might expect between the
larval stages of the different species, the individuals of a single species sometimes differ more from
each other, as regards their metamorphosis, than the individuals of two very distinet species.
This phenomenon has been observed by us and carefully studied in two species—Alpheus hetero-
chelis and Alpheus saulcyi—and it is described in detail, with ample illustrations, in the chapter on
the metamorphosis of Alpheus. In the case of the first species the difference seems to be geo-
graphical, for while all the individuals which live in the same locality pass through the same series

‘

330 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

‘
of larval stages, the life history of those which are found at Key West is very different from that
of those which live on the coast of North Carolina, while those which we studied in the Bahama
Islands present still another life history. In the case of the second species—Alpheus sauleyi—the
difference stands in direct relation to the conditions of life. The individuals of this species inhabit
the tubes and chambers of two species of sponges which are often found growing on the same
reef, and the metamorphosis of those which live in one of these sponges is sometimes different
from thau of those which inhabit the other. In this species the adults also are different from
each other, but as we found a perfect series of transitional forms there is no good reason for
regarding them as specifically distinct, and in the case of the other species—Alpheus heterochelis—
we were unable, after the most thorough and minute comparison, to find any difference whatever
between aduits from North Carolina and those from the Bahama Islands, although their life histories
exhibit a most surprising lack of agreement. In fact, the early stages in the lite of Alpheus hete-
rochelis in the Bahama Islands differ much less from those of Alpheus minor or Alpheus normani
than they do from those of the North Carolina Alpheus heterochelis, and, according to Packard, the
Key West heterochelis presents still another life history.

In the summer of 1881 I received the American Naturalist with Packard’s very brief abstract
of his observations at Key West upon the development of Alpheus heterochelis, and read with great
surprise his statement that this speciés has no metamorphosis, since, while still inside the egg, it
has all the essential characteristics of the adult. As I had under my microscope at Beaufort on
the very day when I read his account a newly hatched larva of the same species and was engaged
in making drawings to illustrate the metamorphosis of which he denies the existence, and as my
experience in the study of other Crustacea had taught me that all the larve of a species at the
same age are apparently facsimiles of each other down to the smallest hair, Packard’s account
seemed absolutely incredible, and I hastily decided that, inasmuch as it was without illustra-
tions and was written from notes made many years before, it involved some serious error and was
unworthy of acceptance. This hasty verdict I now believe to have been unjust, since my wider
acquaintance with the genus has brought to my notice other instances of equally great diversity
between the larve of different specimens of a single species.

The phenomenon is, however, a highly remarkable one and worthy the most thorough exami-
nation, for it is a most surprising departure from one of the established laws of embryology—the
law that the embryonic and larval stages of animals best exhibit their fundamental affinities and
general resemblances, while their specific characteristics and individual peculiarities make their _
appearance later. }

As in most animals the adult life is most important, the adults have a more diversified envi-

“ronment than the young, and the divergent modification which is continually taking place to
perfect the adjustment between such organism and 1ts conditions of life chiefly aftects the adults,
so that specific characters and the slight differences between varieties or races are usually con-
fined to the adults, while the embryos and larve are, a8 a rule, more generalized.

This is true to a marked degree of those animals whose young are nursed or protected or cared
for in any way by their parents, and while it is less true of those animals whose independent life
begins very early, yet the same law holds with them also; and the chief scientific value of embry-

- ology lies in the fact that a knowledge of the early stages in the life of animals enables us to trace
their broad affinities and to distinguish them from more recently acquired differences; for the
early stages of two related forms of life share in common their more fundamental characteristics
and are essentially alike, while the adults differ from each other and exhibit the divergent speciali-
zations which are of more recent acquisition. :

It sometimes happens, however, that the early stages of two closely related species differ
greatly. This may occur when the larve of the one species lead a free, independent life, while the
young of the other species are protected in some way by the parent. For example, the compli-
cated metamorphosis which is so characteristic of starfishes is almost totally absent in those star-
fishes which are provided with brood-pouches. The same relation may also be exhibited when the
larve of one species of a genus have become adapted to a mode of life very different from that of
the larvie of the other species of the genus. Thus those species of Aiginide whose larve are para-

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 331

sitic multiply asexually during the larval life and build up complex communities, while nothing of
the sort occurs in those species with free larvie. ‘4

Many similar cases might be given, but we must bear in mind that they are all very different
from the one now under examination. In ali sach eases the difference is between the larvie of two
distinct species, while in Alpheus we have a similar difference between the larvie of individuals of
a single species.

Among other animals it is not very unusual for certain individuals which are placed under
conditions exceptionally favorable for embryonic development to be born in a more advanced stage
than the normal for the species, and in such cases the larval metamorphosis is abbreviated by the
omission of the earlier stages.

This abridgment of the larval life is not common, but many cases are known, and if the his-
tory of Alpheus were simply another illustration of this process of abbreviation it would not be at
all anomalous; although the existence of three well marked and fixed grades of abridgment in
Alpheus heterochelis, in three widely-separated localities, would still be remarkable and interesting.

The life history of the North Carolina form of this species is more abbreviated than that of
the Bahama form, and the metamorphosis of the Key West form is still more shortened, but, in
addition to the abridgment, the different forms also present most important differences in structure
and in the order in which the appendages are developed; differences which are much more funda-
mental and profound than the mere length of the Jarval life:

The various larval forms are described with so much detail in the chapter on the metamor-
phosis of Alpheus that it is not necessary to repeat them here, but the following very brief outline
will serve to call attention to a few of the most conspicuous features :

As several distinet species of the genus Alpheus pass through a long metamorphosis, each

‘stage of which is almost exactly the same in all the species, we may safely assume thag this is the

primitive or ancestral metamorphosis which was originally common to all the species. It has been
traced in Alpheus minor by me at Beaufort, North Carolina, and by Mr. Herrick in a similar species
at New Providence. Mr. Herrick has also traced it at New Providence for Alpheus normani and
Alpheus heterochelis. In all these forms the larva hatches from the egg in a form which is very
similar to Fig. 2 of Pl. xv1, and very shortly after hatching it» moults and passes into the second
larval stage, which is the one from-which Fig. 2 was drawn. This larva has all its appendages
fully developed and functional as far backwards as the third pair of maxillipeds. Following these
are three bud-like rudiments, to represent the first, second, and fifth thoracic limbs, and posterior
to these a long, tapering, imperfectly-segmented abdomen, ending in a flat triangular telson.

The locomotor organs are the plumose antenn and the exopodites of the three pairs of max-
illipeds. : . ;

After the second moult the larva passes into the third stage, which is shown in Pl. Xv1, Fig. 1,
and Pl, xvu, Fig. 1. The first and fifth thoracic limbs are,now functional; all the abdominal
somites are distinct and movable, and the uropod, or sixth abdominal appendage, has appeared,
and its exopedite is functional and fringed with plumose hairs, while its endopodite is rudimentary.
The five abdominal appendages have not yet appeared.

The first thoracic leg, which was represented by a bud in the preceding stages, has now
acquired a flat, basal joint and a swimming exopodite like those of the maxillipeds, but its endo-
podite is rudjmentary.

The fifth thoracic limb is fully developed and is the most conspicuous peculiarity of the larva
at this stage of development. It has no exopodite; its basal joint is not enlarged nor flattened,
and its long, cylindrical, slender shaft is prolonged at its tip into a long lance-like hair, whieh
projects beyond the tips of the antenne.

After its third moult the larva passes into the fourth stage, which is shown in Pl. Xvi, Fig. 3.

The carapace now begins to extend over the eyes, and the ears make their appearance in the
basal joints of the antennules. There are now five pairs of plumose locomotor exopodites, belong-
ing to the first, second, and third maxillipeds, and the first and second thoracic limbs. Between
the latter and the elongated fifth thoracic limb are buds to represent the third and fourth. The
telson has become narrow and elongated, and the uropods are fully developed, although there is
as yet no trace of the other abdominal appendages.

352 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ow

After the fourth moult the larva passes into the fifth larval stage, when it resembles Fig. 1 of
Pl. xxi, so far as concerns the anterior end of the bod y, from which it differs greatly as regards
the telson and uropods. The eyes are now well covered by the carapace, and the swimming
organs are the seven pairs“of exopodites belonging to the three maxillipeds, and the first four
thoracic limbs. The first five pairs of abdominal appendages are now represented by buds, like
those shown in Pl. xx1, Fig. 1, but the telson and uropods are nearly like those of Fig. 3, in Pl.
xx. The telson is narrow aa much elongated, and its marginal spines are very small.

During the moults which follow. the abdominal appendages become fully developed, the eyes
become completely covered by the carapace, the antennule develops a scale, the antennz elon-
gate, the swimming appendages of the midbody disappear, these appendages assume their adult
form, and the animal gradually becomes like the young Alpheus shown in Pl. xx, Fig. 2.

This life-history is common to Alpheus minor at Beaufort and’ New Providence and Alpheus
normani and Alpheus heterochelis at New- Providence, although the latter species presents a totally
different life-history at Beaufort. Before it hatches, this form, as shown in Pl. xx, Fig. 1, reaches
a degree of development which bears a general resemblance to stages two and three of the es
form, with certain differences which are pointed out in the sequel.

inmadintoly after hatching it assumes the form which is shown in Pl. x1x, Fig. 2, and Fig. 1.
The animal has now all the somites and appendages of the adult, but all behind the maxillipeds
are rudimentary, and there is little power of locomotion. The first»moult occurs in a few hours,
and the larva assumes the form shown in Pl. xx, Fig. 3, when it is no longer a larva but a young
Alpheus. The eyes are almost completely covered by the carapace, the ear is well developed, the
flagellum of the antenna has elongated, and the other appendages have assumed the adult form.
An older specimen is shown in Pl. xx, Fig. 2, and a still older one in Pl. xvu, Fig. 3. Careful com-
parison will show that no exact parallel can be drawn between any larval stage of this form and a
stage of the first form, and that we have to do with something more profound than simple accele-
ration of development. The Bahama heterochelis has, at first, three, then four, then five, and then
seven fully developed and functional exopodites, while the North Carolina form never bas more
than three. As regards the thoracic region and the first five abdominal appendages the Beaufort
larva, at the time of hatching, is more advanced than the fourth larval stage of the Bahama form,
while the uropods are like those of the Bahama form at the time of hatching.

In the latter the first and fifth thoracic limbs are the oldest, and the others appear in succes- |
sion, while all five pairs appear together in the Beaufort form. In the Bahama form the uropods
appear before and in the Beaufort form after the others, andl many minor differences show that we
have to do with profound modification of the life history rather than with simple acceleration.

Packard’s short account of the development of those specimens of this species which oceuy
at Key West shows that these differ from the Beaufort specimens about as these latter differ from
the Bahama specimens.

The second species is probably A. saulcyi, although Guérin’s figure and description of this
form are not in accord with it in some important points. It is found in the Bahama Islands, living
in the tubes and chambers of two species of sponge, a green one and a brown one. Those found
in the green sponges have many small eggs, while those found in the brown sponges have only a
few large eggs. The eggs from the green sponge hatch in the stage shown in Pl. xxi, Fig. 1. It
has rudimentary gills, the eyes are imperfectly covered, the antennules and antenn are beginning
to assume their adult form, and the exopodites of the three pairs of maxillipeds are thé chief organs
of locomotion, although all the appendages are represented. The abdominal feet are rudimentary,
however, and the uropods are covered by the cuticle of the telson.

Very soon after hatching the larva moults and assumes the form shown in Pl. xx1, Fig. 2. The
eyes are more completely covered, the antennules and antenne are elongated, the thoracic limbs
have the adult form and the rien pods are all functional.

In twenty-five or thirty hours after hatching it moults for the aecgua time and passes into
the third stage, which is shown in Fig. 8. It is no longer alarva, but a young Alpheus, with all
the structural characteristics and pugnacious instinets of the adult. , ‘

In a few cases the development of this species is still more accelerated, and a few eggs from
animals taken from the brown sponge hatched in the stage shown in Fig. 8, instead of the stage

.

Z op alt MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 333

% shown in Fig. 1. The following notes on the variations in the coloration and habits in Alpheus,
3 particularly in A. saulcyi, are taken from a paper ee Mr. Herrick published in the J ohns Hopkins
4 University circulars.

VARIATIONS IN THE HABITS AND COLORATION OF ALPHEUS.

.

5 Some of the species of Alpheus are usually or even universally found living as parasites within
By the water tubes of sponges, and it is extremely interesting to find that individuals of the same
x species, living in different species of sponges, may themselves differ greatly in color and in habits.
* A large brown sponge, Hircinia arcuta, which is not to be mistaken, grows on the shallow

reefs and off the shores of many if not all the Bahama Islands. This is called the “ loggerhead
: sponge” by the fishermen, and is found from just below low-tide mark out to one-half a fathom

or more of water, where its great size and sooty brown color distinguish it at once on the
oN ; white bottom. If a sponge colony of this kind be pulled and torn apart, one is certain to find it
, swarming with a small species of Alpheus, which quarter themselves in the intricately winding
pores of the sponge. Hundreds, or even thousands of individuals might be collected from a single
_largespecimen. These animals vary from one-eighth to three-fourths of aninchin length. They are
' nearly colorless, excepting the large chelw, which are tipped with brown, reddish orange, or bright
blue. The females are so swollen with their eggs or burdened with the weight of those attached
: to the abdomen’ that they can crawl only with great difficulty if taken from the water. The eggs
eae : are few in number and of unusually large size, their diameter varying from one twenty-second to
coe ~ one twenty-fifth of an inch, and their number from six to twenty. These are most commonly yellow;
but may be either bright green, olive, flesh color, brown, or dull white.

Another quite different sponge grows on all the reefs in from one to two fathoms or more of
water. There are several varieties of this, which may be told by their olive-green color, yellow
flesh, and clumpy, irregular shape, as well as by the putrescent mucus which some of them pour
out when broken open. In nearly nine out of ten of these sponges one will find a single pair of
Alphei which resemble those living in the brown sponge in most particulars, although they differ from
them in several important points.’ They are distinguished by their large size, and by their peculiar
ee and very uniform ‘color. They vary in length from two-thirds to one and two-thirds inches. The
: females exceed the males greatly in bulk owing to the great size and number of their eggs.

Both sexes are nearly transparent and colorless excepting the large claws, which are bright

as vérmilion-orange (Pl. Iv). The female is practically inert during the breeding season (which lasted

during our stay, March to July), and at such times is well protected in her sponge, or against any.

green surface, by the bright greén ovaries which fill the whole upper part of the body, and by the

mass of similary colored eggs attached to the abdomen below. Only two pairs, or four individuals,

; s out of a hundred or more which were examiried showed any variation from these colors. In these
the eggs were yellow, and the pigment on the claws more orange than red. The table which fol-
lows shows the variations between two large females taken respectively from the brown and green

‘ sponges, and between the size, number, and color of the eggs.
i aig Habitat of Alpheus. | Length of 9 mi of Diamefer. Color. Color of adult,
a e. ra + Fa E
ey Inches. Inches.
Aa 3 Brown sponge.... + 19 vy Yellow (variable). Large chelzw, red, blue,
"th eae a j or brown.
Be “— ; Green sponge . ---- 14; 347 vs Usually green; in this | Large chelw, always
A? : case yellow. orange-red.
Ss These two forms, apparently distinct, are seen however, by closer examination, to belong
uh to the same species, although they show very interesting variations. The Alpheus living in the
- brown sponges tends to vary in several ways, chiefly in size and in the color of the body and eggs.
z, ¥ The rostrum usually has three spines, but occasionally only two are present, the median one being
lost. It is evident that these animals are pertectly protected from outside enemies while within

_ the tortuous mazes of the sponge, as their numbers would show. Parasites such as Isopods, how-

Ss

334 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. AS a

ever, are not uncommon. ‘There has thus been no chance or need for natural selection to act along
the line of color. On the other hand, possibly, the Alpheus of the greet sponge does require color
protection, since the females are very sluggish during the breeding season, which extends over a
good part of the year. This animal is certainly well protected against any green surface, as already
stated. But as will be shown, natural selection has probably nothing to do with it. The bright col-
oring of the tips of the claws, which only are protruded from the place of concealment, recall the
similarly colored heads of boring annelids which abound on the reef, and may have a protective
significance. This evidence, however, is not very reliable. f

The colors of certain crustacea, and also the ‘color of their eggs, are known to vary greatly
with the surroundings. In the Alpheus parasites in the brown sponges these colors vary consid-
erably where the surrounding conditions are the same. However, the color of the ovarian eggs is
always the same as that of those already laid, and although these animals were kept for several days
at a time in differently colored dishes, we never observed any very marked change in the color of the
eggs, but these experiments were not continued long enough or carefully enough to be conclusive.
The eggs of Alpheus hecterochelis are almost invariably of a dull olive color, while as in the case of
the parasite of the green sponge, about one in a hundred has bright yellow eggs. In the first case
at least this is possibly an instance of reversion to one of the original colors from which the green
was derived by natural selection. In most species of Alpheus the color of the eggs is fixed and
uniform, and as already suggested may have a protective significance, but in a few other cases
where this is not true, the color is not only variable in different individuals, but seb also in
the same individual. : ,

In order to explain the variations which we find in these two forms, we must assume either (1)
that the parasites of the green sponge are a fixed variety with distinct habits, or (2) that they repre-
sent individuals which have migrated from the brown sponges and adapted. themselves to their
new surroundings, or further (3) that only those chance individuals with orange-red claws and
bright-green eggs, which occasionally occur in the brown sponge, find their way to the smaller
green species, where they acquire great vigor and size. This last supposition is evidently untena-
ble. If moreover the two forms, which were at first supposed to be specifically distinct, represent
fixed varieties, we ought to find the young or at least adults of all sizes in both sponges, whereas it is
only in the large brown variety that any small or undersized individuals oceur, while a single pair, of
large and tolerably uniform size, is invariably found in the exhalent chambers of the green sponges.

These and other considerations render it probable that the second (2) proposition above stated
is the correct one, viz, that the parasites of the green sponges were born in the brown variety, and
after attaining considerable size migrated thither, where they adapted themselves at once to their
slightly different surroundings, growing to three or four times their former size, and the females
acquiring bright green eggs, which become a source of protection in their new habitat. This view
implies the greatest variability in color and in size of the individual, and in the color of the egg,
which is more remarkable from the fact that it is quite unusual in this genus.

THE EMBRYOLOGY OF ALPHEUS.

At my suggestion Mr. Herrick undertook, in 1886, the study of the embryology of Alpheus,
and devoted a considerable part of his time for three years to this subject, and while he carried on
the work under my general supervision the results which he has reached are entirely his own, and
my share in the chapter which is devoted to this division of the subject is only that of an instructor.
I must call attention, however, to the fact that Mr. Herrick’s studies were begun at a time when
our knowledge of the embryology of the higher Crustacea was far less complete than it is at the
present time. From time to time brief abstracts of the progress of the research have been written
by Mr. Herrick and published in the Johns Hopkins University circulars, and the following cor-
rected summary of his results contains the substance of these preliminary reports.

The work was begun at Beaufort, North Carolina, and the eggs of the two species of Alpheus
which occur there were carefully examined and preserved for laboratory research, but much better
and simpler material was afterwards obtained at the Bahama Islands, the early stages were much
more thoroughly studied, and the development of the animals was traced in detail, step by step, —

" MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 335

from the first nucleus of the fertilized egg, through all the embryonic and larval stages, up to the
adult condition. The eggs of each of the thirteen species. which occur in the Bahamas were ob-
tained and studied sufficiently to ascertain what are the specific differences in development, and
four species were studied exhaustively, in detail. These four are Alpheus heterochelis, Say; A. mi-
nus, Say; A. saulcyi, and the Bahama heterochelis. Unless otherwise stated the following notes
on the early stages refer to the last species. The development in the egg is the same for all, except-
ing A. minor, which will be referred to separately. :

This prawn has proved to be a good subject in which to study the origin aud réle of certain
much disputed bodies, which are met with in several Crustacea, the “‘secondary mesoderm cells.”

SEGMENTATION OF THE NUCLEUS AND OF THE YOLK.

The egg when laid, is enveloped by a single membrane, the chorion or shell, to which is added
the secondary membrane of attachment. If the nucleus is unfertilized, it is not able to initiate the
process of segmentation. The fertile nucleus divides, and its products pass towards the surface,
until a syncytium of eight nuclei is formed. Either just before or after the division of these,
the yolk undergoes segmentation simultaneously over the whole surface into a similar number of
partial pyramids. Each yolk pyramid has a large nucleus at its base, while its apex fuses with
the common yolk mass in the interior of the egg. The process is now a regular one until 128 to 256
small segments are formed. The rate of cell multiplication is then retarded over one-half of the
egg, while it still continues and perhaps is accelerated over the remaining portion of it. The egg
thus loses its radial symmetry and becomes two-sided. It is important to notice that no products
of the segmentation nucleus aré left in the interior of the yolk. The superficial pyramidal
structure is lost; the primitive blastoderm is established, and there now takes place a general
migration of nuclei from the surface to the yolk within, but principally, as would be expected,

‘from that part of the egg where the blastoderm cells are most numerous, corresponding to the
future embryo. This is followed by a partial secondary segmentation of the food-yolk into balls.
The yolk-ball is apparently formed about the migrating nucleus, but as the latter is moving, this
segmentation is irregular.

Mr. Herrick has been able to follow very closely the entire process of segmentation in Stenopus,
where it is substantially the same as that just described, except that there is no general migration of
cells from the surface, prior to invagination. This is also true of Pontonia domestica, and it is quite
probable that the majority of macroura pass through the same phases in their early development.

Alpheus minor is anomalous from the fact that the products of the first nucleus instéad of
multiplying by regular binary division, multiply indirectly, and give rise to numerous nuclei,
many of which degenerate, before the blastoderm is formed.

THE INVAGINATION STAGE.

A slight invagination occurs where the superficial cells are thickest, and the egg becomes
what has been generally regarded as a modified gastrula. The depression is shallow, and does
not form an inclosed chamber within the yolk. The included cells multiply rapidly, and form a
mass of nearly similar elements, some of which pass into the yolk. The protoplasm surrounding the
nuclei of these cells is prolonged into a reticulum, which encloses myriads of small volk frag-
ments, and probably digests them by an intracellular process, after the manner of feeding amcebe.
The thickening in front of and surrounding the pit, which is now obscured, is the rudiment of the
abdomen. Anteriorly the “ procephalic lobes” or more properly the optic disks make their appear-
ance on either side of the long axis of the embryo, as circular patches of ectoderm. Meantime
nuclei wander from the cell mass below the abdominal plate to all parts of the egg. Some pass to
the opposite side, and take up a position beside the flattened epithelial cells, of what was the primn-
itive blastoderm. The majority, however, pass forward and upward in divergent lines from the

' sides of the abdominal plate, and eventually large numbers of these wandering cells settle down
over the dorsal surface of the embryo.

336 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

PRODUCTS OF CELL DEGENERATION. — "

At the beginning of the egg-nauplius period, when numerous wandering cells have passed
forward and joined the inner surface of the embryonic ectoderm, certain new bodies begin to appear
in great numbers. They vary in size from small refringent particles to bodies nearly as large
as ordinary nuclei. The latter stain deeply and nearly uniformly, but with high powers it is
often possible to demonstrate a clearer zone about them, which might be mistaken for a layer of-
cell protoplasm. How do these bodies, the so-called “secondary mesoderm cells,” originate and
what is their function? As to their origin there can be no doubt whatever. They arise by a
process of degeneration from the embryonic cells or nuclei, chiefly from those wandering cells just
described. Many of the latter may be seen to be swollen out and their chromatin divided into
coarse grains and balls of various sizes. The wall of the cell breaks down and thus sets the chro-
matin granules free, or, more correctly, the products of the degenerating chromatin. ;

These degenerating bodies are most marked in the fully developed egg-nauplius, where there
is a large accumulation of them around the csophagus and at the bases of the rudimentary
appendages. After this stage they generally disappear from these regions. Somewhat later,
however, when there is a well developed nervous system and six pairs of post-naupliar appen-
dages, a patch of ectoderm cells on the surface of the egg opposite the embryo proper becomes
noticeable. It reminds one of a median unpaired ‘dorsal organ.” A slight invagination appar-
ently takes place at this point, but at any rate a number of cells pass into the surrounding yolk,
and these give rise in the way described, to a swarm of minute particles of chromatin products.

Before any pigment is deposited in the eyes, it is easy to demonstrate the presence of blood
corpuscles in the stream of plasma which bathes the nervous system. They have the adult
characteristics, that is, they possess a deeply staining nucleus and a clear irregular body. In the
nauplius stage, moreover, some of the larger ‘secondary mesoderm cells” have a similar appear-
ance, but there is no evidence that they ever become blood cells. Mr. Herrick’s study of these
bodies has shown that Reichenbach’s views on the function of secondary mesoderm cells of Astacus
are probably erroneous. According to this naturalist they arise from the nuclei of the endoderm
cells, forming the ventral wall of the primitive stomach, and are converted into mesoderm.

THE GERMINAL LAYERS.

The apparent plasticity of the embryonic cells and layers and the comparative tardiness with
which they are clearly differentiated can not fail to impress anyone who follows closely the early
stages of development. The cell mass developed around the invaginate area, forming the thoracic-
abdominal process, can not be artificially divided into layers. It certainly represents very largely
the primitive mesoderm, but some of its elements pass to the opposite pole of the egg and become
almost indistinguishable from the superficial ectoderm, although it will be shown that they do not
pertain to this layer. A part of this mass remains as the mesoderm of the rudimentary abdomen,
while many of the cells which migrate from it degenerate and perform a nutritive function.

The endoderm does not appear as a definite layer until the egg-naupiius stage. It arises from
wandering cells which assume a peripheral position, and, joining the cells of the hindgut, form the
walls of the mesenteron.

THE EYE.

The optic discs appear as patches of ectoderm, one cell thick on either side of the long axis of
the embryo in front of the rudimentary abdomen. Before the appendages are definitely formed,
these have become thickened ectodermic discs. This thickening is due (1) to delamination, or to

a division of cells in a plane parallel with the surface; (2) to emigration of cells from the surface, _

due to crowding or to a division of superficial cells in a plane at rizht angles to the surface. A dise
of cells is thus formed which gives rise chiefly to the eye and its ganglia. The cord of cells uniting

the two optic dises represents mainly the future brain. The eye proper is due to the differentiation _

of the outer layer of the cells of this disc, while the ganglion is developed from the inner layer.

For fuller results of later studies not represented by these partial and preliminary notes, reference —

must be made to Mr. Herrick’s completed paper and to the summary of the whole history of the
development in the egg given at the end.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 337

GONODACTYLUS CHIRAGRA,

There are few orders of animals of which we are more ignorant than we are of the Stomato-
pods. They are well known as museum specimens, and every natural-history cabinet contains one
or two, which have been brought home as rare curiosities from distant seas; but we know hardly
anything of the habits of the living animals. They are abundant and widely distributed, but like
most rapacious animals they are very alert, taking alarm at the slightest disturbance and retreat-
ing to the depths of their burrows at the bottom of the ocean, where they are so completely hidden
fiom observation that their capture is difficult, and any attempt to study them in their homes is
almost out of the question.

The habits of Squill are tolerably well known, and in my report on the Stomatopoda, collected
by H. M.S. Challenger, I have given an account of the habits of Lysiosquilla based upon observa-
tions made at Beaufort, North Carolina; but, except for afew scattered and fragmentary notes in
the various descriptive papers, this is the whole of ow: knowledge of the order. During the sea-
sons of 1886 and 1887 I was so fortunate as to find in the Bahama Islands Gonodactylus chiragra
living in localities which were peculiarly favorable for observing its habits, and I am now able to
supplement my report upon the Challenger collections by an account of this interesting species, of
which little had hitherto been known, except the fact that if is the most cosmopolitan of the
Macroma abounding on the shores and islands of all tropical and subtropical seas.

I also obtained its eggs in abundance and succeeded in rearing the young from them in
aquaria, and am now able to make a contribution to a subject upon which there were hitherto no
direct observations, for it is a noteworthy fact that while the older larve of Stomatopoda have
long been known, and while many genera and species of them were carefully figured and described
and named by the older naturalists before their relationship to the adult Stomatopoda was sus-
pected, not a single species in the whole order has, so far as I am aware, been reared from the
egg and in this way identified with its specific adult.

While the adults usually inhabit burrows in the bottom the larvae swim at the surface of the
ocean, and as none of the animals which are captured in the surface net exceed them in beauty
and grace, their glass-like pelagic larve are familiar to all naturalists who have had an oppor-
tunity to study the surface fauna of the ocean. Their perfect transparency, which permits the
whole of their complicated structure to be studied in the living animal, their great size and
rapacity, the graceful beauty of their constant and rapid novements, can not fail to fascinate the
naturalist. Unfortunately they are as difficult to study as they are beautiful and interesting, and
notwithstanding their great abundance and variety, only two or three of them have been traced
to their adult form.

Unlike most Malacostraca the Stomatopoda, instead of carrying their developing eggs about
with them, deposit them in their deep and inaccessible burrows under the water, where they are
aérated by the currents produced by the abdominal feet of their parents. The eggs quickly
perish when deprived of this constant current, and as itis very difficult to obtain them at all, I know
of no Stomatopod which has ever been reared from an egg under observation. The older larvie
are hardy and are easily reared, but they areseldom found near shore, and microscopic research
is so difficult at sea that I know of only two cases in which they have been kept until they assumed
the adult form. As I have stated in my report on the Challenger Stomatopoda, I haye reared a
young Lysiosquilla excavatrix from an old larva which was captured at the surface, and Faxon
has in the same way obtained the young Squilla empusa. The young larve are common near
shore, but as they seldom survive a moult in captivity they can not be identified in this way.

The growth of the larve is slow and the larval life long, and as they are as independent and
as much exposed to changes in their environment and to the struggle for existence as the adults
they have undergone secondary modifications which have no reference to the life of the adult, and
are therefore unrepresented in the adult organism. The larvee have been arranged in genera and
species, but their generic characteristics are quite different from those upon which the adult genera
are based, and this is true in a still greater degree of their specific characteristics. As they
undergo great changes during their growth different stages have been described as distinct species
or even genera, and it is not easy to select from the rich gatherings which are brought home by

S. Mis. 94 22

338 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

collectors the successive stages in the history of a single species. Like the adults, they are widely
distributed, and a gap in a series from the North Atlantic may be filled by a specimen from the
coast of Australia or the Sandwich Islands, and the collection from a single locality may contain
the larvee of several widely-separated species of adults in all stages of growth as well as the larve
of deep-water species which are as yet entirely unknown.

The attempt to unravel the tangled thread of the larval history of the Stomatopods is there-
fore attended with very exceptional difficulties, and the earlier writers were content to rest after
the bestowal of generic and specific names upon the larve. As I found after the Challenger collec-
tion was placed in my hands that it was very rich in larve, I attempted to determine, by compari-
son, the larval series for each genus, and the methods which I employed for making the comparison
are fully stated in my report. As one of the results of this comparison I ventu.ed to describe the
general characteristics of the larva of the genus Gonodactylus (p. 113), and in PI. x11, Fig. 5, of
that report I figured a larva which I ventured to call the larva of Gonodactylus. A comparison of
that figure with Pl. xv, Fig. 11 of this memoir will show that this determination was correct, for
the larva of Gonodactylus chiragra which is here described is so much like the one figured in the
Challenger report that they belong, in all probability, to the same species.

~

CIPFA PTE RR. It.

THE LIFE HISTORY OF STENOPUS.
By Franots H. HERRICK.

This paper is the result of observations made at Beaufort, North Carolina, in 1881 and 1833,
and at Nassau, New Providence, in 1887, The marine laboratory of the Johns Hopkins University
was stationed at the latter point in the Bahama Islands from March until July of that year, and
with the means thus generously. afforded, I was able to considerably extend my studies upon the
Crustacea of these coral islands.

Professor Brooks found a number of peculiar pelagic larvee at Beaufort, and it is very probable
that they represent a part of the life history of Stenopus hispidus. Plates 1x and x, illustrating

- two important stages of these very interesting larve, are contributed by Professor Brooks, and
4 the descriptions of these stages are based entirely upon his observations

While the material gathered in a sojourn of afew months at the seashore is in many instances

incomplete, it seems worth while to bring out this sketch of the Stenopus, inasmuch as nothing

was previously known of its development, and indeed but very little concerning the adult form.

Stenopus hispidus is, in-fact, generally known to naturalists as occurring only in the Indian and

South Pacific oceans. It was at first quoted from the Atlantie (Cuba) by Von Martens (7) in 1872,

and it has not since been reported from the Western Continent, so far as we are aware, until we

7 rediscovered it at Abaco, Bahama, in 1886, but any assiduous collector on West Indian coral reefs
. must somewhere have hit upon it (v. Appendix I). 7

As the eggs are quite small, as is the case in all Crustacea with a protozoa stage, they are not
particularly well suited for study by means of sections, and no special attempt has been made to
trace out the history of the germinal layers, a subject which can be dealt with to better advantage
in other species. The Stenopi breed readily in aquaria, and several series of eggs, illustrating
fully the segmentation, and some early phases of development were prepared, and the sections
were afterwards made in Baltimore. These are given on Pl. vi. They are especially interesting,
since the segmentation is like that of Peneus studied by Haeckel, who relied wholly upon surface
observations. ;

The ova were immersed in Kleinenberg’s picrosulphuric acid and afterwards hardened in
alcohol. This answered sufliciently well for the purpose in hand, although it rendered the eggs
more resistant than is desirable.

I.—THE NASURAL HISTORY OF STENOPUS.

pit The Bahaman Stenopus (PI. vy) measures from 14 to 1? inches in length. All the appendages
are long and generally quite slender and delicate, especially the antennie, which give to this fori

Rg a very characteristic appearance in the sea. These are snow-white. They are carried widespread
7 and arch outwards in graceful curves. The flagella of the second or outer antenne are two and a
as half times the length of the body. In the act of swimming these are bent backward and outward,

while the outer division of the first or inner antenne is carried upward, and their inner branch is
. dizected forward. ,

The body is pure white or nearly so, excepting three broad transverse bands of reddish scarlet.
The first or most anterior of these color bands covers the front of the animal, involving the eyes

2 and bases of the antenn, and in some cases it extends behind the rostrum as far as the mandib-
< 339

340 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

ular or “cervical” groove. The second is nearly confined to the broad tergal surface of the third
abdominal segment, While the third zone crosses the last abdominal somite and impinges on the
tail fin. The appendages are all colorless excepting the third pair of legs which carry the large
pincers. These are similarly marked with four bands of the same bright color, As shown by the
colored plate two of them encircle the great claws, a third belongs to the carpus, and the fourth
to the meros or fourth segment of the limb. The bases of the third and sometimes of the fou. ch
and fifth thoracic legs are tinged with bright blue. The ovaries often give to the dorsal surface
of the females a light-greenish cast.

There is but little variation in the size and character of these markings in the same sex or in
different sexes, but it is most remarkable to observe how constant these colors are in individuals
of the species from different parts of the world. We possess two colored drawings of this spe-
cies* (which will be referred to again), one by Adams (5), from a living specimen taken in
the China Sea, and the drawing of Dana (6), who found the species on the coral reef of Raraka,
one of the Paumotu Islands, and at Balabac Passage, north of Borneo. Both of these, and especially
the Samerang plate, essentially agree with our Bahaman specimens, which in color seems to be
the more faithful copy of nature. Here the basal joints of the thoracic legs are colored blue as in
the Nassau form. Why should Stenopus, coming from different seas, retain the same colors and
markings, to a nicety of shade and pattern, while a cosmopolite like Gonodactylus chiragra (a Stoma-
topod) presents such wide color variations as to be as unlike as possible, so that scarcely any two
taken from the same place have a similar color pattern? To this question we can not at nee
give a satisfactory answer.

Alcohol soon removes all trace of color from the body, but the spots on the legs remain for a
longer time as light orange pea Both sexes are of nearly the same size, and, as already stated,
alike in color.

Being thus brilliantly decorated with the American colors, our crustacean soon acquired with
us the name of the “ Bandanna Prawn.” As we see this animal swimming deliberately in the
water we are reminded of some strange and fantastically colored insect. It is by far the most
showy, and for its size the most attractive, member of that giant family, the Crustacea, which
have their dwelling on the reef. One day, when out upon a wading and diving expedition, a pair
of these prawns was discovered by turning over a plate of loose coral, and was easily captured by
slowly raising the slab from the water into the boat; for this species, unlike some shrimps, is quite
helpless when once out of its element. More frequently, however, they led us to a long chase.

There seems to be considerable attachment between the sexes, since they are invariably found
in pairs, the male and female swimming side by side. On a still day they may be found clmging
to the mosaic of sponges and living coral, which form the reef bottom, but if disturbed they sud-
denly become very active, and, darting backward by sudden jerks, dive into some chink, out of
reach of the hand net.

Several females both hatched and laid eggs in aquaria in the month of June, but the breeding
season, as inferred from the capture of locomotor larve, probably extends throughout the spring
and summer months, if not throughout the entire year.

The eggs are very numerous. They are nearly spherical and measure one-fiftieth of an inch
in diameter. They were always of the same light opalescent-green color. The ova are laid at
night, but the process was not observed.

Three different females hatched their broods on the afternoons of June 4, 14, and 24, respec-
tively, and moulted and laid eggs during the following nights. As these animals invariably moult
just before laying their eggs, the latter are probably fertilized at the time they are laid. The
hatching of one brood lasted about 9 hours, from 2 o’clock in the afternoon until well into the fol-
lowing night. By 10 o’clock the same evening some of the larve had moulted for the first time.
The eggs are closely felted to the abdomen, and, as in all Decapods, they are cemented together
by a secretion which possibly comes from the oviducts during ovulation. They are fastened by
the same substance to the hairs which fringe the bases of the pleopods, chiefly to those of the first
and second pairs.

i Be wide s Milne- Edw ards feune (4), evidently made ons a specimen in which the natural colors had been removed
by alcohol. (See remarks, ete., under Section Iv.)

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 341
After a moult the colors are, as is usual, very bright, and the moulted skin, as it stands intact
supported by the antennz, may easily be mistaken for the living animal. These prawns make no
sounds and appear to be very timid. The surface of the whole anterior body and of the large
claws is thickly beset with tooth-like spines, the points of which are bent forward, and these
may be regarded as an admirable protection against being swallowed head first by an enemy. It
is also interesting to notice that the spines of the hinder part of the body project backward, and
may thus be of service to Stenopus when attacked from the rear. Their long sensitive antenne or
“feelers” and well-developed eyes doubtless warn them of approaching enemies, which, by their
rapid angular movements, they may easily escape. The extraordinary development of the eyes in
the older larvee (Pl. 1) is remarkable.
: The geographical distribution of Stenopus hispidus is very interesting.* H. Milne-Edwards,
in his “ Histoire naturelle des Crustacés” (3), gives the habitat of Stenopus hispidus (Latreille) as
the “Indian Ocean,” following Olivier (1) and the older writers. In the “ Régne Animal” of
Cuvier, third edition, ‘‘ Les Crustacés,” p. 137, he says: ‘‘ We know of only one species, reported
from the Australian seas by Peron and Lesneur.” The Samarang naturalists (5) met with it on
the coasts of Borneo and at the Philippines in 1843-46. Dana, in 183842, on the Wilkes Expe-
dition (6), found it in the South Pacific at the points already noticed. In 1872 E. von Martens (7)
describes the species for the first time from the Atlantic, in a collection of Cuban crustacea made
by Dr. J. Gundlach, and de Man in 1888 (9) quotes it from Amboina in his monograph on the

Decapoda and Stomatopoda collected in the Indian Archipelago by Dr. J. Brock.

- We can now add to this list the Bahama Islands (Abaco and New Providence). We have
also the interesting fact that the larva was taken on our coast at Beaufort, N. C., whither it had
probably been carried by the warm waters of the Gulf Stream. We may thvrefore expect to find
the adult Stenopus on the Florida Keys, but not much farther north, since this is essentially a
tropical form.

We thus have in Stenopus hispidus anether instance of not only the same genus, but also the

- identical species, occurring on the eastern shores of two continents. It seems not impossible that:

the prolonged larval period which this animal possesses may have played an important part in its

geographical distribution. This may be also true of Gonodactylus chiragra, but on the other hand

it can not be asserted of Limulus. In the last case the Asiatic and American forms are specifically
distinct.

Il. SEGMENTATION AND EARLY PHASES OF THE EGG.

The prawn, which hatched her zoéa brood on the 4th of June, laid eggs the next morning prob-

ably at about 6 o’clock, and as soon as discovered some of these ova were hardened at intervals of

. a few hours during the next two days. In this way a complete history of the segmentation was
obtained.

First stage.—The first eggs preserved (probably 5 to 6 hours after ovulation) are perfectly
opaque, nothing but the light-green yolk corpuscles showing through the shell or egg-envelopes.
Thin sections prove that the segmentation nucleus has divided, and that its two products lie remote
from each other. Physiologically speaking, we now have two cells, each consisting of a deeply
staining nucleus and perinuclear protoplasm. The first segmentation is evidently central. What
takes place is briefly as follows: Primitively wé have a central nucleus, about which protoplasm
is gathered. Around this again is the great mass of yolk, and the whole is encapsuled by the
protective chorion and the secondary membrane of attachment. The first division involves only
the nucleus and surrounding protoplasm. The_products as independent bodies now leave their
central position and seek the surface of the egg. In one instance one of these has reached the
surface (shown in PI. v1, Fig. 1), while the other is only halfway there on the opposite side. The
superficial cell, as seen by the figure, has the same characters as when buried in the yolk. In

* The reason for considering the Bahaman form identical with the Hispidus of Olivier, Latreille, Milne-Edwards,
Adams, Dana, and others are given on page 351.

342 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

another egg of the same phase neither cell is quite at the surface, so that the example given in
Fig. 1 may be taken to illustrate a tendency, not arule.* The yolk (Fig. 1, Y. C.) consists here,
as in subsequent stages, of homogeneous and tolorably uniform green Foy _No vacuolar
cavities are to be seen.

Second stage.—Four and one- aoe AES later the second segmentation is going on or is already
completed. The egg from which Fig. 2 was taken contains four nuclei with perinuclear protoplasm.
It was cut into a series of 50 ies of which the second represented is the twenty- first. Nuclei
occur in sections 21, 25, 29, and 35, none being as yet superficial. A portion of section 21 (Fig. 2)
is shown under a higher power in Fig. 3.

Third stage.—A fter three hours and twenty-five minutes have passed the third phase is ‘seacked
and we have eight cells, around whicb the yolk is superficially constricted into eight corresponding
lobes or segments. A surface view of this entire egg and also a section through it are shown in PI.
vi. Figs. 5 and 6, and a tangential section of one of the nuclei and lobes is given with more detail in
Fig. 4. The constriction furrows appear to be considerably deeper than they actually are, and we
might predicate a total segmentation of this egg without the knowledge which the section affords.
We have here a merely superficial indentation of the yolk, the great central mass of which is undi-
vided. ~ It is a close approach to the yolk pyramid stage seen in Astacus, Alpheus, Hippa, Pala-
monetes, and many other Decapods. The dividing planes, Figs. 7 and 8 (unless artificially pro-
duced), do not penetrate into the egg. The furrows extend inward to a plane just below or on a
level with the nucleus. : .

Each nucleus with its outer protoplasm may be spoken of as the cell, and it is hardly probable
that there is any protoplasm like that surrounding the nucleus in the other parts of the egg. The
nuclei increase gradually in size, as seen by comparing the figures of successive stages, and the
surrounding plasm, which they manufacture out of the yolk, is also of greater bulk. Each is a
flattened, oval disc, shown well in transverse section in Fig. 5 at a, and tangentially in Fig. 4.
It contains coarse grains and granules of chromatin, and the enveloping protoplasm radiates visibly

but a short distance between the yolk spherules. The long axis of each nucleus lies in a plane ~

parallel with the surface. Cell multiplication is in all cases indirect, as my observations show to
be the case with several other related forms, and this is undoubtedly the rule not only with the seg-
menting eggs of the Decapod Crustacea, but with those of all the Metazoa. There seems to be an
exception in the case of Alpheus minor.

Fourth stage—After another interval of an hour and five minutes there are sixteen cells re-
sulting from the fourth segmentation. The blastomeres are less sharply marked at the surface and
more distinctly polygonal. Six nuclei are cut by the section given in Fig. 7. They are nearer to
the surface than in the former stage.

Fifth stage-—The egg represented by Fig. 8 is three hours older than the last and has thirty-
two cells and the same number of superficial segments. Up to this time the egg has exhibited
radial symmetry. The nuclei are quite near the surface of the egg. They are more spherical and
the investing protoplasm is less conspicuous than formerly. The fissures between contiguous
blastomeres are becoming less and less prominent. ;

Sixth stage—After a longer period, nine hours and forty-five minutes, the process of regular .

division into smaller and smaller superficial segments has proceeded until 128-256 of these bodies
are formed. The cells lie at the surface, just under the chorion, and form a continuous envelope, the
primitive blastoderm about the central yolk. This yolk mass is not segmented, nor does it include
any nuclei which have not participated in forming the blastoderm. In one or two instances a cell
was observed just below the service. This may be interpreted as either having never reached the
surface or as having been there and moved below it towards the interior. But the general state-
ment is doubtless true that all cells reach the surface, and that there is no extensive migration to
the interior, as there is in Alpheus, before invagination.

* It now seems ardbaple to me that this papeenaiad cell represents the male and the eentral cell the female pro-
nucleus. A small, deeply staining body, which I interpret as an undoubted polar cell (not shown in Fig. 1), lies
underneath the chorion, not far from the superficial cell.

MEMOIRS OF THE NATIONAL ACADEMY OF SOLENCES. 343

Seventh stage.—In three hours and three-quarters from the last phase the blastodermic cells have
spread more rapidly at a given point on the egg, which loses its radial symmetry in consequence.
There is thus formed the embryonic area or first trace of the embryo proper.

Highth or invagination stage.—Three and a half hours later a portion of the blastoderm in the em-
bryonic area is invaginated, that is to say, some of its cells pass below the surface in a body, and
the invagination stage is reached. The invagination is solid, or nearly so, as is the case with
nearly all Decapods. Fig. 9 represents an oblique section of one end of an egg, through the area
of invagination, Ig. The epiblastic cells contain small oval nuclei. There are no yolk cells in the
interior of the egg. The vitellus is bere segmented into large, irregulaz fragments, each of which
is composed of yolk corpuscles similar to those seen in Fig. 4. It is just possible that this fracture
of the yolk, which is commonly seen in the eggs of other Crustacea, is artificially produced at
least to some extent, at this stage.

Ninth stage-—After another period of three and a half hours, while the external change is not
marked, the invaginated cells have rapidly multiplied and given rise to a considerable cell-mass
below the surface at that point.

Tenth stage.—In thirteen and a half hours from the last stage, or when the embryo is fifty-two
hours old, important changes have been effected. In surface view the embryo presents a heart-
shaped or somewhat three-sided area. The optic discs appear as widely separated patches of
ectoderm, united to the thoracic-abdominal plate, a mass of cells which forms around, but chiefly
in front of, the point of ingrowth. Sections through this egg show a considerable thickening in the
optic dises, and an accumulation of large granular cells in the abdominal area. These latter un-
doubtedly represent some of the primitive mesoderm and endoderm.

The phenomena just recorded are given in a more condensed form in the following table,
which shows the age and corresponding growth of the embryos at the successive stages. The age
of the first stage is assumed to be 6 hours, which is probably not far from the truth. )

In the above account we are constantly dealing with different eggs, and assume of course that
they are all at any given time in the same phase of development. -While this is not strictly true,
it is very nearly so. The eggs are at first about on a par, and it is only later that some become
handicapped, producing those slight differences which may be seen in embryos from the same
female.*

Time of hatching June 4, a.m.,early. Temperature 80° F. Diameter of egg »; inch.

Age ofegg. State of developmeut,

Stage.
Poy Glirsis ooo deems = 2 cells
% pla 5 9 7: eee ee 4 cells.

3 | 14 hrs. 55 min..... 8 blastomeres.

4, | 16 irs ey oes. 16 blastomeres.

Gp halouirerc sss es _ = 32 blastomeres.

6 | 28 hrs. 45 min. .... 128-256 blastomeres.
Vl ie ee First trace of embryo.
8-| Sagres So So. 2s. oe Invagination stage.

9+ 38s bra\.secscccc cba Pit obscured.
10} 52.hra..........-.. Optic discs and abdominal plate formed.

We thus have in Stenopus a type of the so-called “ centro-lecythal” segmentation, exactly
comparable to that of Penzeus, and essentially like that which is probably characteristic of a
large number of the Decapod Crustacea. The fact that all the protoplasm of the egg enters into
the blastoderm and that no yolk cells are now formed, is of some interest, and this subject, will
be considered more fully in a paper on the development of Alpheus.

* This is not true of the American lobster, Homarus americanus, in which I have made a very complete study of
the segmentation process. In a batchof segmenting lobster’s eggs, there is a decided lack of uniformity. Some ova
which afterwards continue to develop, remain with yolk unsegmented until the third or fourth day after fertilization.

344 MEMOIRS OF THE NATIONAL ACADEMY OF SOTENCES.,

Ill. METAMORPHOSIS, OR PERIOD FROM THE TIME OF HATCHING TO THE ADULT STATE.

A. Protozoéa or first larva (length=4™™).—Stenopus leaves the egg as a protozoéa, which may
be compared to one of the early larve of Penzus or Sergestes, but it is unlike either of them.
This first larva,which is very long and slender, is so coiled upon itself in the egg that the tail fin
overlaps the posterior end of the carapace. It requires considerable time after casting off the
shell to uncoil and straighten its appendages, especially the antenne and the long rostrum which
was bent under its body. 2

The figure on Pl. x1 exhibits some of the grotesqueness of this larva. This drawing was made
from an animal which had’ just wiggled out of its egg shell and was uncoiling its appendages.
The huge antenne are partially unfolded, while the rostrum R., is scarcely visible. Drawings of
parts of this immature protozoéa are seen in Pl. vu, Figs. 11-16, and the larva itself as it finally
appears, about two hours after hatching, in Fig. 11. If we compare with this the younger form in
Fig. 25, we notice some details, chiefly of a quantitative kind, in which they differ. Immediately
after leaving the egg the epidermic structures grow rapidly ; hairs or sets are developed ou all the
appendages, and the tail-fin acquires some new characters. The first larva does not swim well
until several] hours after hatching.

The Stenopus protozoéa (Pl. vi, Fig. 11) is 4™™ long, the rostrum alone being 13™™. It is color-
less, excepting the dark eyes and a few scattered blotches of brownish pigment upon the sides of the
body or on the tail-fiu, It swims chiefly by aid of its largely developed antenne, which are directed
forward as shown in the plate. These, with the rostrum, add considerably to the apparent length
of the body and serve to distinguish it, without the aid of a lens, from the second larva (Pl. vi,
Fig.17), which soon follows and swims about in the aquarium with the others. It is further character-
ized by the very large size of its mandibles (Pl. x1, Fig. 25, Md.) and by its forked telson-plate,
adapted for swimming. The forked locomotor tail-fin and large hairy antennz mark the protozoéa
stage in Crustacea generally. The carapace is only feebly developed, not nearly reaching to the bases
of the appendages. It is prolonged in front into a huge tapering cone, the rostrum, which is nearly
half the length of the body, This is beset with short spines and reaches considerably beyond the
antenne. About four segments of the abdomen are distinguishable from before backwards (Fig. 25).
The first and second, which latter is the largest, carry lateral spines, and the upper surface of the
second segment is also prolonged posteriorly into a median spine. The tail-fin at the time of hateh-
ing is sharply forked (Fig. 13) and is furnished with 6 pairs of rudimentary sets, of which the
median pair is the shortest, besidvs a pair of outer non-plumose bristles (Figs. 11, d, and 13, a.). In
the course of a few hours this organ has become functional and appears as shown in Fig. 11. The
hairs grow out and acquire thick lateral fringes; the outer pair (next to a) become rudimentary,
and three additional pairs of toothlike bristles make their appearance on the sides of the telson-
plate. por
The eyes are sessile. The inner or first antenne (Fig. 25, Al) are jointed, unbranched append-
ages. Each is tipped with a bunch of about four long sensory filaments and with a single seta. A
single plumose hair also springs from the distal end of the penultimate joint on its inner side.
The outer antenne are biramous. The inner branch consists of a simple stem, tipped with at
least two long hairs. The outer division is segmented at its extremity, and is garnished with
plumose set, chiefly on the inner margin, there being one or two to each segment. The gland at
the base of the antennal peduncle is conspicuous.

The mandibles are of enormous size in comparison with the other appendages. A view of the
labrum and right mandible is given in Pl. yu, Fig. 15. They are simple blades with rounded
edges, covered with minute horny teeth. There is no palpus. The first maxilla (Fig. 12) consists
of two stout branches tipped with bristles, and in the case figured they are spotted with pigment.
The second maxilla is a broad lobulated plate (Fig. 10). Each Jobe is provided with hairs,
excepting the outermost which corresponds, in part certainly, to the secaphognathite. Only a
single bristle was detected on this lobe in the specimen from which the drawing was made.

The three maxillipeds have each an exopodite, which is considerably larger than the other
branch, and which is furnished near the tip with not less than three pairs of locomotor hairs. The
undeveloped condition of these latter in an embryo just hatched but unable to swim, is well shown by

a

MEMOIRS OF THE NATIONAL ACADEMY OF SOIENOES, 345

Figs. 14 and 16, which represent the first and third mavxillipeds of the right side, as seen from
below. The endopodites of the second and third pairs possess four joints, of which the terminal
one carries set. There is one pair of thoracic limbs consisting of a stout locomotive exopodite,
similar to that of the second and third maxillipeds just described, and of a very short, indistinetly
segmented endopodite. The latter is armed with two terminal and three lateral plamose hairs on
the inner side.

B. First zoéa or second larva (length, a=5™"),—Five or six hours after hatching the pro-
tozoéa moults into a form which superficially resembles the macrouran larval type. (Pl. Vm,
Fig. 17.) The carapace of this larva has grown down so as to cover the basal joints of all the
appendages, and it also extends behind them. The rostrum is reduced to from one-half to two-
thirds its former size, and does not surpass the antennal hairs.

There is still put one thoracic segment with its appendages. All the abdominal segments are
formed, but none show any traces of limbs. The lateral spines of the first and second somites are
missing, but the median unpaired spine of the latter is greatly developed, and extends to nearly
the end of the third somite. The sixth somite, which carries the zoéal telson, is equal in length to
the third, fourth, and fifth combined. The fan-shaped telson, viewed from below, is represented
in Fig. 20. Comparing this with Fig. 11, we observe that it is no longer conspicuously forked.
The median notch has a short unpaired spine. There are six pairs of feathered hairs, the outer
ones still being rudiments exactly as in the first larva, and a non-plumose spine which ends the
series; the three rndimentary spurs seen in Fig. 11 being wanting. The eyes, which have acquired
short stalks, protrude slightly.

The antenne are shorter and are now no longer so important as organs of lecomotion. The
terminal joint of the inner antenna is reduced, but otherwise this appendage is but little changed.
The outer antenna ends in a stout hook, which is succeeded, on the indented margin of the inner
side, by a series of eight feathered hairs. The second joint of this appendage also bears a serrated
hooked spine at its outer extremity. The mandible is without a palp. It has a serrated edge,
and a prominent, inferior, compound tooth (Fig. 18).

The inner branch (coxopodite) of the first maxill (Fig. 19) carries three simple and three com-
pound spines, while the outer division consists of three segments with stout, plumose hairs, as shown
in the figure. ‘Lhe second maxillie (Fig. 21) are considerably altered from the form shown in Fig. 10.
There is an outer lobe (scaphognathite), bearing one large hair directed backwards and at least
four others which point in the opposite direction. The inner portion is lobulated into six or more
parts, allof which are well provided with stiff hairs.*

The first maxilliped is shown greatly enlarged in Fig. 22. Examining this in connection with
Fig. 14, we find that the exopodite consists of one segment and bears a limited number of hairs
(here two) at its apex. The endopodite is segmented and carries numerous hairs, which are
continued in small tufts along the inner margin to the base of the limb. The chief swimming
organs are the first and second maxillipeds and the first pair of thoracic legs. The inner branch
of the latter is considerably developed, and nearly equals the expodite in length.

There is a large irregular spot of red pigment on each side of the anterior half of the body
just above the base of the third maxilliped. The lobes of the liver (L) begin now to show dis-
tinctly through the carapace. The food yolk, which is present in small quantities in the stomach
of the protozoéa (Fig. 25), is finally absorbed. It was probably owing to this and to the fact that
I gave the lar¥ no food that suited their taste that they never reached the second moult, although
they passed a number of days in this condition. In course of several trials the animals at this
stage always became greatly crippled by particles of organic matter adhering to their body and
invariably starved. For later stages, therefore, connecting this zoéa with the adult, we have to
rely upon larve collected at the surface of the ocean.

©. Mysis or Schizopod stage—lIt is evident that the zoéa of the stage B passes into a mysis-
like form through the intervention of one or more moults, and we have two larve already noticed
belonging to the close of this period. They were collected by at Beaufort, N. C., July 14 and 15,

* The distal or terminal lobe represents the endopodite; the lobes next this stand for the basipodite, while the
second (?) proximal division at the base of the appendage correspond to the coxopodite.

-

346 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

1883. In the Beaufort specimen (Pl. rx) all the segments and appendages of the body are present,
and all of the latter are functional, excepting the first five pairs of abdominal feet, which are
rudimentary buds. The carapace is well developed, and terminates in front in a slender serrated
rostum, which is much shorter than in previous stages. The eyes are now large and prominent,
being mounted on long stalks. These organs, which are sessile in the protozoéa, undergo marked
changes in both size and form in the course of development. They reach a maximum in a later
stage, and are correspondingly reduced during the passage from the latter to the adult.

The inner antennz are biramous; the outer are reduced to a long narrow scale, armed with
bristles. The third pair of maxillipeds and first, second, third, and fourth pairs of thoracic legs bear
prominent swimming exopodites. The fifth pair of pereiopods characterize this larva by their
great length, and by the huge, paddle-shaped segment, which bears the small, terminal claw.
There is no exopodite to this appendage. The endopodites of the first, second, and fourth pereio-

pods are nearly equal; the third longer. The first five abdominal segments are of equal size.

and, as stated, carry rudimentary feet. The sixth segment, however, is long and narrow, and has
the uropods well developed.

D. Mysis stage.—The larva of stage C moulted into a form (P1. X) resembling the last, with the
addition of several important features. The inner antenne consist, as before, of a segmented stem

with two terminal appendages. The first and third segments of the antennular stalk are short, —

while the second is very long; spine nearly equal to length of basal segment; inner flagellum
very slender, shorter than the outer branch; the proximal, thickened portion of which carries
several (three) bunches of sensory filaments.

The antennal seale is as long as the antennular peduncle. The flagellum of the antenne now
appears as a slender filament, nearly twice the length of the scale. Possibly it is formed, as in
Penzeus, from a bud-like remnant of the inner ramus of this appendage in the protozoéa. The
third pair of maxillipeds and first to fourth pairs of thoracic legs are as in the previous stage, with
conspicuous exopodites fringed with sete. The endopodite of the fourth pair is longer than that
of the third; the fifth pair are twice as long as the fourth; and the breadth of the penultimate
segment is much reduced.

The first, second, and third abdominal segments are equal; the sixth is narrow, equal to length
of fourth and fifth. The telson is narrow, tapering, three times as broad at base as at apex; the
uropods are one-fourth larger than telson. Pigment is found as before, in the extremities of the
segments of the appendages. Large spots also appear on the abdomen and eyes.

BE. Mastigopus stage—On June 15 an older larva than the one just described was obtained in
the ocean outside the harbor at Nassau. It agrees in the main with the mastigopus of Sergestes.
The carapace ends anteriorly in a short spine or rostrum, which is bent up at an angle of about 40
degrees with the body. The eyes are mounted on very long naked peduncles. Both pairs of
antenn are biramous. The outer flagellum of the first or inner pair of antennie is the longest (Pl.
x1, Fig. 26), and it bears four or five bunches, containing in all about a dozen sensory filaments.
The inner branch is a bad. The second antenne extend as far forward as the joint of the first
pair, where the inner flagellum is given off. The HES of the second pair is wound into a
short spiral coil. -

The exopodites of the second pair of maxillipeds are rudimentary (Pl. x1, Fig. 31). The third
maxillipeds are now the stoutest appendages, and equal in length che third pair of thoracic limbs.
The first and second thoracic legs are slender; the third pair is the longest and thé terminal seg-
ment is bifid; the fourth is a short two-jointed rudiment; the fifth, corresponding to the huge
oar-like appendage of stage C, is reduced to a bud. J¢ thus appears that, as in the Sergestids, the
last two pairs of walking legs are shed after the mysis period, to be reconstructed again in the masti-
gopus stage.

All the abdominal appendages are functional. (PI. x1, Fig.27.) The last segment of the abdo-
men is nearly equal in length to the three preceding. It is onal compressed, and more nearly
resembles the adult form. In the act of swimming this larva carries the abdomen bent at nearly
aright angle to the rest of the body. It is colorless, excepting areas of red pigment at the bases
of the abdominal feet, and spots on the lower portions of the antennz and eye-stalks. There is
also a transverse band of the same color on the anterior part of the carapace.

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 347

PF. Mastigopus stage.—After it had been kept three days this larva passed through 1 moult,
by which only slight changes were introduced, The fourth pair of walking legs is now distinetly
jointed, the fifth remaining as a bud. The flagellum (endopodite) of the second pair of antenue
uncoils and speedily lengthens. The terga of the first and second abdominal somites bear on the
lower lateral margins of each side a short tooth. The larva lived four days without further eedysis.
Figs. 26, 27, 30, and 31 are from this stage.

G. Mastigopus stage [Pl. x1, Figs. 28, 29, 32-34, Pl. xm], (Length = 9"™).—An older larva,
caught in the net on May 7, is shown on P|. xm. The most striking features of this form are the
long trailing antennze (flagella of the outer pair), the actual length of which is about 1 inch, which
is more than twice the length of the larva. The remarkable eyes which this animal possesses give
it a very odd appearance. They are placed at the extremity of club-shaped stalks, each of which
is nearly 2" long. The distance between the eyes is 4.7™. In passing to the adult stage the
eye-stalks are much reduced. The outer antenne have a short peduncle; along seale, armed
with stiff hairs on the inner margin, and a long flagellum, all very much as in the adult prawn.
(Pl. xu, and PI. xm, Figs. 40,41.) The first pair of antenne are much less like the adult form. (PI.
xi and Vig. 40). Thestalk is longer and more slender than in the full-grown condition. The
flagella are short, the inner one still rudimentary, and the sensory hairs are retained.

The carapace has developed on it a lateral furrow, which is surmounted by a conspicuous
spine placed on either side at a point one-third the distance from the rostrum to the posterior end
of the carapace. The rostrum is short and stout, bent upward, and does not reach beyond a line
passing through the vesicula auditoria. The front of the carapace bears also a short dentiform
process on each side below the rostrum. These are the only indications of the fature spinous
armature of this region of the body. The abdomen and abdominal appendages are about as repre-
sented in Fig. 27. The telson is a short triangular plate, garnished with short bristles, and is
terminated by a pair of very small spines. The uropods are provided with a close fringe of inter-
locking, plumose hairs, which are Jongest on the inner margin. The outer lamella is one-third
longer than the inner and three times as long as the telson.

The first and second maxille of this larva are represented in Figs. 28 and 29. In Figs. 12, 19,
29, and 38 we have four stages in the evolution of the first maxilla, and we see that it undergoes
comparatively little change. No trace of a palpus (endopodite) was seen in the specimen exam.
ined (Fig. 29), the appendage consisting of a small inner (coxopodite) and a larger outer knob-
shaped branch (basipodite), each armed with short tooth-like spines. The second maxilla has also
the adult character. (Figs. 28, 42.) It consists of an elongated outer plate (scaphognathite),
fringed with a single row of plumose hairs; a palp-like endopodite, and an innermost lobulated
division (basipodite and coxopodite), each part carrying a few bristles.

The first maxilliped of stage F is given in Fig. 30. It consists of a basal portion (coxopodite),
which bears an inner and larger lobe (basipodite), having bristles on its proximal border; an exo-
podite tipped with a pair of bristles, and of an intermediate bud (endopodite) bearing a single
bristle. Part of the second maxillipeds is shown in Pl. xr and also in Fig. 31 (St. I'.). The
exopodite is rudimentary. The outer segments are covered with spinous bristles. We see already
a resemblance between these appendages and their adult forms. (Figs. 43, 45,) The third pair of
maxillipeds are still the largest limbs. (Pl. x1, Mxp. m1.) The terminal joint bears several long
spines. Compare with the adult limb seen in Fig. 46.

The pereiopods are slender appendages, of which the third pair are longest, as in the adult;
the second are longer than the first; the fourth and fifth are rudimentary. One of the first pair
of pereiopods is represented in Fig. 33. This appendage is nonchelate, unlike the adult stage; all
its segments are armed with long spines, and there is a cluster of serrate bristles on the inner side
of the proximal end of the terminal segment, and near it a similar cluster on the next. Similar
tufts of hair are found on the adult appendage. (PI. x11, Fig.47.) The terminal joint of the see-
ond thoracic limb is shown in Fig, 32; the basal extremity of the third, the fourth, and fifth are
given in Fig. 34. The second and third pair are chelate; the fourth is rudimentary; the fifth is
stilla bud. The abdominal appendages, excepting the sixth pair described above, are all unira-
mous. (Fig. 27.)

348 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

This larva is colorless, excepting large spots of reddish pigment, distributed much as in the
previous stage. There is a spot near the extremity of the eye-stalk and similar ones-on the abdo-
men. Some of the appendages are also tipped with brownish red. The attainment of the adult
characters is now mainly a question of the further growth of parts already present.

The above outline gives us a pretty complete history of the metamorphosis of Stenopus.
Between stages B and © a lacuna occurs, but it is not difficult to bridge over this gap. The
development of Stenopus is especially interesting, inasmuch as it combines certain features of the
metamorphosis of Penzeus, Sergestes, Lucifer, and the Prawns in general, but it differs essentially
from any of them. - Detailed comparisons are purposely omitted in this paper, but we will call
attention to the apparent similarity of the second larva of Stenopus (PI. vim, Fig. 17) to the zoéa
of Callianassa subterranea, figured by Claus.* The length in each case is 5™™, He says, p. 54:

Die jungen Callianassa larven besitzen beim Verlassen der Eihiillen eine ansehnliche Grésse, sind sehr lang-
gestreckt und tragen drei spaltiistige Fiisspaare, von denen sich das Vordere schon wesentlich der Formgestaltung
des spiiteren Maxillarfusses niihert. Der lange Stirnschnabel, sowie die Bestachelung des Abdomens, dessen zweites
Segment mit einem besonders langen Riickendorn bewafinet ist errinern an die oben beschriebene larve.
which applies perfectly to the Stenopus zoéa, except that the latter has the first thoracic segment
with its appendages, while, according to Claus, the first zoéa of Callianassa has not, although his
figure is not clear on this point. The rostrum, eyes, antennz, second maxillez, and maxillipeds
are nearly identical in the two forms. The differences are in the shape of the telson and in the
condition of the thoracic appendages. ‘The tail fin has a convex posterior edge, a median and two
lateral, short spines, and eleven intermediate pairs. The rudiments of the sixth pair of abdomi-
nal appendages show through the integument. Behind the maxillipeds, already “die kurzen,
schlauchformigen Anlagen simmtlicher Thoracalfiisse unter dem Integument bemarkbar sind.”

Among the Prawns, Penzus has apparently preserved most completely the ancestral history
of the Decapod Crustacea, and for this reason a thorough knowledge of the development of related
species is very desirable.

IV. THE ADULT.

STENOPUS (Latreille).
Cancer (Herbst). .
Palemon (Olivier).
Stenopus (Latreille) Léach, Desmarest, Roux, Milne, Edwards, Adams, Dana, ete.
Diagnosis of Stenopus hispidus (Latreille).—Body nearly cylindrical. Carapace with prominent rostrum and
distinct transverse groove. Outer antennz with long, bristle-bordered scale bent under the inner antennz
toward the middle line. Second maxillipeds with epipodite and long exopodite. Third mazxillipeds very

long and appendicular, with a rudimentary exopodite at base. First, second, and third pairs of pereiopods ©

chelate. The first and second pairs quite slender, ending in small shears. Third pair longest, bearing the
large claws. Fourth and fifth pairs of pereiopods slender and nonchelate. Carpus and propodus of the same
articulated into numerous rings. First pair of pleopods uniramous in both sexes, all the others biramous.

Special description.—Length, 37-44™” (14-13 inches). Thereis little difference in size between
the sexes, but the females are usually a trifle the larger.

Color: Body invariably white, crossed by three bands of reddish crimson. Appendages col-
orless, excepting the third pair of pereiopods, which are encircled by four wide zones of the same
color. These markings are not of uniform tint, but vary from bright scarlet to mottled orange red.
The basal joints of at least the third and fourth pairs of thoracic legs sky blue. Antennz snow
white. For further particulars under this heading, see P]. v, and See. 1.

The carapace (Fig. 37) presents a marked transverse fossa. It is covered with short dentiform
spines, largest on the front. The rostrum is elevated, extending hardly beyond the basil joint of
the inner antenn. It ends in a sharp terminal spine and carries six to seven stout, curved teeth
on the dorsal median line, besides a single spinule projecting downwards near the tip. From-the
single dorsal row of teeth two similar rows diverge, extending back to the transverse furrow. The

*C. Claus: “ Untersuchungen zur Erforschung der genealogischen Grundlage des Crustaceen-Systems.” Wien,
1876. Taf. vin, Fig. 1; also Figs. 2-7. :

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 349

rostrum also bears on each side a single row of about four teeth projecting forward. The under
side is unarmed. Several large spines occur in the angle behind the eye and on the basal joints of
the antenne.

The epidermic spines, which are characteristic of the Hispidus, though not confined to this
species, are found upon the dorsal surface of the entire body, on the third pair of pereiopods and
on the bases of the appendages generally. The first, second, fourth, and fifth pairs of thoracie
legs are destitute of conspicuous spines. The spines of the carapace and anterior abdominal terga
are bent forward ; those of the fourth, fifth, and sixth abdominal somites and of the tail fin are
appressed, stouter, nondentilate, and point backwards.

The telson is arrowhead-shaped; its free edges are garnished with short, closely set hairs; it
has a median groove, bordered on either side by a longitudinal elevated ridge, bearing spines; it
hardly surpasses the uropodal lamelle. The eyes project at right angles to the long axis of tne
body. They have dark brownish black pigment and are mounted upon short, stout stalks, covered
with small prickles. The labrum consists of a semicircular bar, the convex surface of which points
forward and bears two nearly median spines projecting downward. From its concave border is
suspended a lingulate appendage, which is supported by a thin, median, and vertical plate. The
inner antenne (Fig. 40) bear very long flagella, the disposition of which has already been noticed
(Sec. 1). The segments of the stalk are armed with stout denticles, and each division of the

- proximal portion of the outer flagellum or exopodite bears externally a sharp spine.

The outer antennw (Fig. 41) possess at their base a long, narrow scale (exopodite), which is
traversed by longitudinal grooves. Their inner borders, which meet in the middle line, are fringed
with closely set hairs. The stalk or protopodite is spiny, and the flagellum or endopodite is two
and a half times the length of the body of the animal. The mandibles (Fig. 39) bear very large
palpi, and have blunt interlocking teeth; a transverse farrow divides the cutting surfaces of each.
The first pair of maxillz (Fig. 38) consist of an inner (coxopodite) and outer branch (basipodite),
with a slender endopodite. The outer division or coxopodite is thickly beset with strong spines.
The second pair of maxillz (Fig. 42) are furnished with an elongated plate, the “bailer” or
scaphognathite, which is fringed with hairs, an inner lobulated portion (basipodite and coxepe-
dite), and an intermediate endopodite, which bears several plumose hairs at its distal end.

The first pair of maxillipeds (Fig. 43) consist of an inner lobulated portion (coxopodite and
basipodite), thickly studded with short bristles, an outer triangular plate (epipodite), and two
intermediate appendages. The innermost of the latter (endopodite) terminates in a stout spine.
It consists of two segments armed without by a row of long plumose hairs. The whip-like,
appendage exopodite next this is twice as long and is bordered with short hairs. In the second
pair of maxillipeds the basil portion consists of several lobules, tufted with hairs, and a small,
external epipodite. There is a stout incurved endopodite, with hirsute terminal joints, and a Jong,
slender exopodite. A transparent lamella springs from the outer side of the proximal half of the
the endopodite, and bears plumose hairs on its free margin.

The third pair of maxillipeds (Fig. 46) are long and conspicuous, somewhat less slender
than the first or second pairs of thoracic legs. The inner and outer borders are fringed with
long hairs. The outer border is deuticulated; the distal extremities of the segments, as of the
ischiopodite, produced into asharp spine. The basipodite is small, bearing the persistent and rudi-

“mentary exopodite, which is a slender palp equal in length to the ischiopodite. The first pair of

dereiopods (Fig. 47) are small, slender, and chelate. The second pair of pereiopods are similar to
the first pair, but longer.

The third pair of pereiopods, the “ great chelx,” differ somewhat in size, the right being some-
times larger and sometimes smaller than the left. The chela is compressed and slightly twisted.
There is a single row of stout regular denticles, forming a saw-tooth edge on either margin of the
** palm,” and several rows of lesser spines on the broad sides. There is also a longitudinal groove
extending to the base of the dactyle. The carpus is prismatic and bears about five rows of large
teeth. The ischium is more cylindrical, but similar. The dactyle and propodus possess each a
prominent tooth, which fits into a corresponding depression.

350 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

The fourth pair of pereiopods (Fig. 48) end in short bifid dactyles, the terminal claw bearing
a shorter proximal one below. The propodus is superficially segmented into from five to seven
rings, which vary in size. The right propodus may have five rings, the left seven. The carpus is
articulated into ten to twelve segments, commonly twelve, of variable or equal size. The fifth
pair of pereiopods is similar to the fourth, but shorter. The propodus bears from six to seven seg-
ments, the carpus from eight to twelve. In the fourth and fifth thoracic legs the number of
rings into which the propodus and carpus are divided differ within the above limits in different
individuals of either sex and on the right and left sides of the same individual. The pleopods are
all biramous, excepting the first pair, in which the endopodite is suppressed as shown in Fig. 44.
This pair of appendages is much smaller in the male. In the female the first swimmerets are
nearly as long as the following pairs and are fringed with long sete.

Measurements (in millimeters).

[ Locality: Nassau, New Providence, Bahama Islands. ]

Length from tip of rostrum to end of telson ....-..--..-.---
Length of carapax, including rostrum..-.-..--.--.----..-----
Greatest breadth, including spines ..-..--.--..--.-.--------
Greatest depth, including spines ...---.-..-...-.-.---.-.---
Length) ofrostrimeers eas seee sesh eee en ee eee
Distance between transverse furrow and tip of rostrum --.. -
Length of first abdominal tergum -...---.---.---..--.-.----
Length of second abdominal tergum.-.......---.----.-------
Length of third abdominal tergum ....-.-......---.-----.--
Length of fourth abdominal tergum..s-....----.-----------.
Length of fifth abdominal tergum .....-..------------------
Length of sixth abdominal tergum -....--.-.-.---..-----.--
Lénethy of telsonis sa. te ee eee eee ee aan eae tees
Gratest (breadth of telson. --2= ~225.-- sees oes eee eee eee
Lieneth of-eye-stalkoac, o-eicae cee eee ee oe een aoe
Greatest diameter of eye = --- 2. 2---2-)22 2. o-oo nee one
Breadth between 6yes 5--:2 226 cose seme ese ae emtine = Seem
Stalkvofinnerantenn® oe jo-co pease ieee ae ee eee
Length of terminal segment of the same---..---------------
Length of inner flagellum of the same....-....-------------
Length of outer flagellum of the same-_-...--..-..----------
Length of scale of outer antenn® .-.-....-.-.-----..--.-.---
Greatest bread th ofthe same=- = 2 a. eee
Length of stalk of outer antenne --...--..-------.----.-----
Breadth of stalk of outer antenna .--. ---- yee tee ee eee
Length of flagellum of outer antenn® .-...--.--------------
Breadth of flagelluin of same at inner end -...--.--..-..----
Length of third maxilliped__--.--. ---- --.----. .-.2 ==-.---.-
Length of terminal joint of the same ........---.---.-.-----
Length of basal joint of the same -=-. -2-._....-2:2--.-----
Breadth of basal joint of the same... --..--..---..--..-----
Length of exopodite of the same -....-...-.--.-..--..----.-
Lien eth:oF first:pereiopod soi tir, went ance te oe ate eee
Length of-propodus of same.--- 2. - - 55. eo sece enn eee eno ce
Breadth of propodus of same.=.. ..2-s--- -5- -- 2 oho one oe -
Length of dactyle of Sameé-s= 22-0 - -ae ee eee ne nese sees inae ase
Length ofearpus) of same... e.c> seat as aeee ee eee ae ae
Hengeth ofsecond pereiopod ene seesaeee > eee eae eee
Length of propodus of same.... ---. ---.---.---- ---2 ---- =
eng thof dactyle of same... - 2 - 2c Soe - ons nnn aeempeeeee
Breadth of propodus of same 22. ------ -- see eee ee eee
Héneth of carpus ofsame 7-3. —- - eo <2 oes cee eee cee
Length of meros of same ..-.---.---- = aeizkee see peta eo =
Length of left third peretopod ....---.-.-----.---- --s-<-----
LGN PUO MONO My st ec one Clap win sens ares od a ten SO ee ae
Greatest breadth of same with spines -...---.--..-..-.-----
Greatest depth of same with spines.....--.-.-.-.-.---.-----
Ligne thopaacnvless cP a4 sec siecsciset ot at epee ct cl eee

Mencth.ofcarpus Of samotes eo ees eset eco ee eee
Greatest breadth of carpus without spines.---..-.-...------
Greatest breadth of carpus with spines ......-.--.----..----
Length of meros of ‘same. = ssc -aeccniscseieace bees cceeeee
Length of right third pereiopod ...- 02. ce cece eene cone cues

s
MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 351
Measurements (in millimeters)—Continued.
SOK. cena cece ne enn nce c ew encamenswacn sce sacewneesecescccccwascnenncs fos ? fo t. t
baad |
Length of chela of the same.......-.--.--.---+..--.--..---- 18 LG acne aes
Greatest breadth of same with spines -.-..-.--.-.-.----.----- 5 ME bse eoce cd tee
Greatest depth of same without spines ....--.-....---.----- | 4 Stet \ areal mene | eee
BlGn Po OM ACuy le OUGAMO Somme eeeseeen sae sen cieldn ce sow fh 08?) c02|5- S222] sacs oe| sconce
Width over tooth Of daonyle:—tas4- ee denna tee nm nnd ose. senee>-| 2 -f5-s--.)--<--- fo seat lscamee
Length of carpus of right third pereropod --...--.----. ------
Greatest breadth of same with spines.....--...------.------
Greatest breadth of same without spines -.
Length of meros of same ..-..-.. --02 ---- «2 - E
Length of fourth pereiopod -... 25. c0ese conn cane --newcesee :
ERE OL OADbVIE OF GANIC j2-22.0 duinsien|oucdaven 7s <uens ssl en
Length of propodus Of BAMO\;..-5. J2aecsasa cane seem eens cane
is Number of rings in propodus...... 2... 02.0 22.5 2220 cee. ----
Eonpill of carpus Of 8AM) 20. . 22060-22222. odes aneeaanaan
NOM Ven OP TINTS It CALPUsiss. 2 2a < eos aeons c--7 eances a= oho
Length of meros of same.../.-..---- Ao pe on nee ccer |
Greatest breadth of meros......-....--...------------------ aa
Ven gtly oMitnt POFOlOPOd. <- 2. -sacn oon caea ense -2 ooto sen -aesn) OO
Length of propodus of same.--. .... .... ---.---- ---- ---+ 2-0 5
Number of rings in propodus...:......-.....-2.0.-...----.-| 6
Length of carpus of same <2. 22.25 6... 222 ese sees woes wsen| 15
INUMIOE Gh EIS OT OANDNS!scecanJe. cane wedsecaeansaea~ eoeet elo
Length of meros of same 1 9.5
Length of first pleopod ..-. .-. 3
Men Pa Bere Pleo NO wesc sa sso sue wo Tanase shale o> Goe~ oes |poke es
Length of inner lamella of same....-../---.----.--.-------- 4
Breadth of inner lamella of same.......-..-----------.-----| 1.5
Length of outer lamella of same... ........---.------------ A
Length of inner lamella of uropod.-......-....----.-------- 6.5
Length of outer lamella of uropod..........--.--..---22---- Carn
Greatest breadth of outer lamella of uropod ............---. 3

ReEmMARKS.—The earliest figure of Stenopus lispidus with which I am acquainted is that of »
Olivier, published in 1811 under the name of Palwmon hispidus (1, Pl. 19, Fig. 2). In this drawing
the third thoracic leg of the right side is represented as rudimentary. In explanation of this he
says: “La pince gauche manquoit et paroissoit repousser. Dans un autre, ’étoit la droite qui
manquoit et paroissoit repousser de méme.” The next drawing appears in Milne Edwards’s Atlas
(3, Pl. 25, Fig. 13) of 1837. Like Olivier’s plate this is crude and faulty.

A second and very much better likeness of the Hispidus by Milne Edwards came out in
Cuvier’s Le Régne Animal (4, Pl. 50, Fig. 20). This is represented as pale straw color and was
evidently made from an old alcoholic specimen. Some of the parts are also figured. Adams’s
figure (5, Tab. x11, Fig. 6), already noticed, and his brief description agree essentially with the
Nassau form. The antenne are not in their natural position, and should probably be more
than twice as long as represented. Of the habits of the species he says: ‘The Stenopus, Sicy-
onia, and Peneus, usually swim in a slow, deliberate manner forwards, and occasionally with
a sudden jerk propel themselves backward. They keep at a considerable distance from the shore
and seem to love deep still water, never appearing when the surface of the sea is ruftled.”
The drawing by Dana (6, Pl. 40, Fig. 8) represents the antenn of this animal for the first time
in a natural position. The antennal and antennular stalks are, however, much too slender, com-
pared either with Adams’s figure or with the Nassau form. The length is given as 3 inches, while
the Stenopus on the plate measures about 24 inches. So far as it goes his description agrees in the
main with my own. He says: ‘The legs of the first and second pairs and of the fourth and fifth
are colorless, and they are extremely slender, much more so than in the drawings hitherto giving
of the Hispidus; third pair is about one-fourth longer than body, fourth joint of second pair nearly
twice as long as hand; fourth joint of fourth pair 12-jointed,-and fifth joint 7-jointed; tarsus
minute (p. 606).” :

This extreme slenderness does not appear in the specimens examined by me, nor is it apparent
in Adams’s figure, which is one of the previous drawings referred to by Dana. In making the
drawing of the Nassau Stenopus (Pl. v) great pains were taken to represent all the appendages

dog MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

in their natural positions, and in their true relative proportions. In Adams’s plate the fourth
joint of the fourth thoracic leg has 16-17 rings, the fifth joint 8 rings. In the Nassau form’the
carpus has 10-12, the propodus 5-7 rings. In details like this, where the right and left sides of
the same iaaiecine are often unlike, it would be surprising to find agreement. Von Martens’s
short notice of the Cuban occurrence does not give us much additional knowledge, but there is no
doubt that the alcoholic specimens examined by him belong to the same species as that described
in this paper. He says: ‘‘ Ich weiss keinen erheblichen Unterschied zwischen diesen cubanischen
Exemplaren und den indischen anzugeben, welch letztere ich bei Amboina gesammelt habe. *
* * Nur erscheinen die indischen im Leben bunt roth gezeichnet, in Spiritus blass orange und
mehr hartschilig, endlich scheint Carpus und Hand des dritten Fusspaars bei ihnen minder vier-
seitig, doch ist dieser letztere Unterschied gering und fliessend.” He then adds that he would
not be surprised if it should turn out that the West Indian form was specifically different from the
East Indian. x

So far then as we can judge from the figures and meager descriptions in our possession, the
Asiatic Stenopus hispidus can not be regarded as specifically distinct from the American form.
Perhaps a point of difference worthy of remark is the length of the body from rostrum to end of
telson, which is given as 24 and 3 inches by Adams and Dana respectively. None of the Nassau
specimens which I have measured were more than 1? inches long. The data upon this point are not
conclusive, and, in view of our knowledge of local variations in this respect, can not be regarded
as of much importance. It is hoped that the descriptions and measurements which are here given
will afford a basis for future comparisons with the Pacific Stenopus hispidus.

List of species.
So far as I can learn, only five species of the genus Stenopus (Latreille) have been described, viz:

(1) Stenopus hispidus (Latr.):
Distribution: (a) Indian Ocean, Borneo, and Philippines (Adams).
(b) Paumotu Islands and Balabae Passage, north of Borneo (Dana).
(c) Amboyna, Cuba (Von Martens).
(d) Abaco and New Providence, Bahama Islands.
(c) “Red Sea, Indian Ocean, Indian Archipelago, New Guinea” (de Man).
(2) Stenopus spinosus (Risso) :
Mediterranean (Heller), teste Von Martens and de Man.
(3) Stenopus ensiferus (Dana):
Fiji Islands.
(4) Stenopus semilevis (Von Martens) :
(One specimen in the Berlin Zoélogical Museum, purporting to have come from the West Indies. Length 12™™,
Von Martens. )
(5) Stenopus teruirostris (de Man) :
Amboyna: Length 24™™, (More closely allied to Stenopus spinosus of the Mediteranean than to Stenopus
hispidus, and is the representative of the former in the Indian Ocean ; de Man.)

STENOPUS LITERATURE.

(1) Olivier: Encyclopédie Méthodique, Hist. Nat. Insectes, t. viii, p. 666, 1811.

(2) Latreille: Encyclopédie Méthodique, Hist. Nat. Crustaces, Arachnidses, et Insectes, t. 10, rage 1882.

(3) Milne Edwards, H.: Hist. Nat. des Crustaces, t. 2, p. 406, 1837.

(4) Milne Edwards, H.: Le Régne Animal, Cuvier; Les Crustaces, with Atlas, by Milne Edwards, p. 137.

(5) Adams and White: The Zodlogy of the Voyage of H. M. S. Samarang, 1843-6, p. 61, London, 1850.

(6) Dana, J. D.: U.S. Exploring Exped. U. S. N., 1838-1842, vol. xiii, pt. 1, Crustacea, p. 607.

(7) Martens, oh v.: Ueber Cubanische Crustaceen ; nach den Sammlungen Dr. J.Gundlach. Archiv. f. Naturgesch.,
38. Jahrg., Bd. 2 , 1872, p- 143.

(8) Heller: Grentaneea des siidlichen Europa, 8. 299. (I have seen only references to this paper.)

(9) De Man, J. G.: Bericht tiber dieim indischen Archipel von Dr. J. Brock gesammelten Decapoden und Stomato-
poden. Separat-Ausgabe aus dem Archiv. f. Naturgesch., 53. Jahrg., pp. 215-600, 17. Taf., Berlin, 1888.

.

CHAPTER III.
THE HABITS AND METAMORPHOSIS OF GONODACTYLUS CHIRAGRA.

By W. K. BRooKs.

(With Pl. 1, 11, xtv, and xv.)

THE STRUCTURE AND HABITS OF THE ADULT.

.

This well-known species is found along the shores and islands of all tropical and subtropical
seas, and our collections contain specimens from the Atlantic, the Pacific, and the Indian Oceans.
Among the many localities where its presence has been recorded the following may be named:
Bermuda, Florida: Keys, Bahama Islands, Cuba, St. Thomas, Brazil, Mediterranean, Cape St.

~ Roque, Samboanga, Samboanga Banks, Nicobars, Red Sea, Amboina, Indian Ocean, New Guinea.

It is subject to but little variation, notwithstanding its very wide distribution, and also notwith-
standing the fact that there are several other distinct species of Gonodactylus extremely similar
to chiragra, and distinguishable from it by only very minute differences. There is a well-marked
chiragra-like group of species all so close to each otber that their divergence from each other must
have been comparatively recent, and in view of this fact it seems remarkable thaf one of these
species should so persistently retain its identity when exposed to such a wide diversity of
conditions.

The species may be thus characterized: Stomatopoda with the sixth abdominal somite sepa-
rated from the telson by a movable joint; the hind body convex; and the dactyle of the raptorial
claw without spines and enlarged at the base; rostrum consisting of a transverse proximal portion
more than twice as wide as long, with subacute antero-lateral angles and a slender, acute median
spine which does not quite reach to the bases of the eyes; carapace nearly rectangular, three-fifths
as long as wide, leaving the dorsal surface of the second thoracic somite completely exposed ; an-
tero-lateral angles semicircular and projecting beyond the median gastric area, which is nearly flat,
and bounded by two nearly parallel gastric sutures, which are continued to the posterior edge of the
carapace, which is nearly transverse with rounded postero-lateral angles; the transverse cervical
suture is faintly marked, distané from the anterior margin about two-thirds of the length of the
carapace; second thoracic sonfite, somewhat narrower than the carapace, with acute lateral angles;
the eight following somites equal in width and wider than the carapace; the third, fourth, and
fifth thoracic somites about equal in length; the lateral margins of the third are straight, with
rounded angles, and as wide as the dorsal portion; the fourth is narrowed a little towards the
lateral edge, and the fifth still more so; dorsal surfaces of the free thoracic somites and of the first
five abdominal somites smooth ; hind body convex; all the abdominal somites have marginal lateral
earine, which are nearly linear, with the anterior end only a little wider than the posterior end;
postero-lateral angles rounded in the first four abdominal somites, rectangular in the fifth, and
acutely pointed in the sixth; there are no dorsal carine on the first five abdominal somites, and
no median dorsal carina on the sixth, which carries three pairs of swollen convex lateral carine,
which are equal in length and end posteriorly in acute spines, which are occasionally wanting
on the submedian pair; the external carina is much less swollen than the others, and it unites
at its posterior end with the laterial marginal carina; the spines of all the carinz project beyond
the posterior edge of the somite and lie in the same transverse plane.

S. Mis. 94-23

353

354 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

The fifth abdominal somite is somewhat longer than those in front of it, and about twice as
long as the sixth. The telson sometimes presents.slight variations, but most of its characteristics
are well marked, so that there is usually no difficulty in distinguishing the species by examining it.
It is considerably wider than long, and its median portion is occupied by a rounded prominence,
which consists of three broad, convex rounded carinz, none of them ending in spines; the median one
is longer than the others and spatulate at its posterior end, while the others have both ends obtusely
rounded and alike; external te the proximal end of each lateral carina, and almost directly under the
tip of the second, or intermediate dorsal carina of the sixth abdominal somite there is a small polished
hemispherical tubercle. The edge of the telson is folded into six teeth, of which the submedians
are largest and project farthest backwards; the tips of the intermediates are distinct and reach
about half way to the tips of the submedians; the laterals are obsolete on the dorsal surface, al-
though thin, small tips are distinctly visible on the flat ventral surface of the telson; each of these
six teeth carries a dorsal carina; that of the lateral is marginal and nearly linear, while the others
lie in the dorsal axes of the teeth and are thick and convex; that which lies above the submedian
tooth is short, and lies in the same longitudinal plane as the external carina of the median promi-
nence of the telson, while that which lies above the intermediate tooth runs nearly to the anterior
edge of the telson; the median edges of the submedian teeth are minutely serrated. slightly con-
cave, and meeting at an acute angle. There is a minute, nearly obsolete, tooth in the angle be-
tween the submedian and the intermediate, and the tips of the submedians are occasionally, but
exceptionally, tipped by movable acute spines. The dorsal surface of the basal joint of the uropod

ends posteriorly in an acute spine with a small lobe on the outer side of the base: its ventral sur-.

face ends posteriorly in a curved process divided into two acute curved spines, of which the outer
is much the stouter and usually considerably longer than the inner, although they are occasionally
nearly equal; the outer one has no marginal tooth. The paddle of the exopodite is about half as
long as the second joint, which carries a central terminal immovable spine, and usually eleven—
rarely twelve, and still more rarely ten—movable spines, of which nine are marginal and the tenth
and eleventh terminal, largest, and central to the paddle. The eyes are cylindrical, with rounded
cornez, and the first and second antenne are about equal in length, and more than half of the
second joint of the shaft of the first antenna is exposed in front of the eye.

In the Bahama Islands this species presents two well-marked color variations, which occur
side by side, specimens of both sorts being often found in burrows less than an inch apart. In the
one form the color is a uniform dull-olive without BpObs or markings of any sort, as shown in Pl. 117;
while the other form, which is copied in Pl. 1, Fig. 2, is more transparent and is delicately inpitind
over the entire dorsal surface in an SE but Senatant pattern of greyish-green pigment so
distributed as to form three transverse bands across the carapace and the large joints of the
raptorial claws and fine transverse bands across the telson, while over the rest of the dorsal
surface it forms a complicated reticulam. This difference is not sexual, for I found both males

and females of each color; nor is it distinctive of age, for, while all the largest specimens were otf’

the uniform green color, I found specimens of each color of all sizes except the largest. It is not
probable that there are two constant color varieties living side by%side in the Bahama Islands,
and J am disposed to think that the mottled transparent specimens are those which have recently
moulted, and that the color becomes more uniform as the cuticle hardens.

In the Bahama Islands this species inhabits burrows which it constructs in the coral reek ov
in masses of coral in shallow water, and, as nearly all the localities where its presence has been
recorded are in the coral area, it is probable that this-habit is pretty generally retained by the
species all over its habitat. I have found it most abundant in lagoons and sounds on shelving
beaches which are bare or nearly bare at low tide; and when a beach of this description is over-
hung by a limestone cliff, from which fragments fall into the water, each fragment is honeycombed
by their burrows. A crack or natural depression in the rock seems to be selected by the animal

when about to construct a new burrow, for most of the burrows opened into such cracks. The

mouth of the burrow is nearly circular and only a little larger than the body of its inhabitant, but
just within it widens out into a flask-shaped cave (PI. 111), with smooth, even walls and regular
curvature, and large enough for the animal to coil up or turn around insideit. Most of the burrows
are horizontal, but many are vertical with the opening below, and a few are vertical with the
opening above.

+9 at On

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 35D

The animals usually rest coiled up, with the eyes and antenn directed outwards, just within
the mouth of the burrow. They are always on the alert and reach out and snap at every small
animal which approaches, even when it is two or three times larger than the Gonodactylus. They
rarely pursue their prey, at least in the day time, and while a bait held near the mouth of the bur-
trow will usually tempt them as far out as the body can be stretched without leaving the burrow
they seldom go any further. In aquaria they are much more active at night than in the daytime,
and they may possibly wander more in search of prey at night than I have ever seen them do in the
daytime. They are solitary in their habits, and Ihave never found two in the same burrow. They
are pugnacious to an astonishing degree, and their fighting habits, as I have observed them in
aquaria, are so fixed and constant that they must be constantly exercised by the animals when at
hume. When two specimens are placed together in an aquarium they at first appear to be un-
conscious of each other, but more careful examination will show that their eye stalks are in con-
stant motion following each movement of the enemy. They soon assume a position in which they
are face to face, although they may be on opposite sides of the aquarium, and the constant motion
of their eye stalks shows how intently each movement is watched. Soon one attempts to get be-
hind the other, but each such attempt is frustrated, until finally they are brought close together,
face to face, and soon one springs suddenly upon the other and attempts to pinch some unprotected
part. They then spring apart and eye each other again to repeat the attack at short intervals
until one is disabled; the other then springs upon him and soon tears him limb from limb, dis-
jointing all the free somites of the body and tearing out and devouring the flesh.

I was not able to learn how the burrows are made, for none which I kept in captivity made
burrows. The regularity and smoothness of the burrows and their adaptation to the shape and
size of the body indicate that they are constructed by the animals themselves. The habit of bur-
rowing in hard rock instead of soft mud is a fortunate one for the naturalist; for, while it is almost
impossible to obtain the eggs of an ordinary Stomatopod without using a steam dredging machine;
it is easy to get those of Gonodactylus by breaking up the rock in which it lives.

While adult Stomatopods are abundant and widely distributed, their eggs are almost unknown,
for most of them inhabit deep burrows under the water, where it is no easy matter to capture the
adults, and even when these are caught they do not carry eggs even in the breeding season, for
the eggs are not fastened to the appendages as they are in most Crustacea, but are deposited at
the bottoms of the inaccessible burrows. As they are dependent upon the aération which is pro-
duced by the current of water which the parent pumps through the burrow by means of the valve-
like paddles of the abdominal feet, they die when deprived of this current. The eggs are sometimes
obtained, but unless they are found in an advanced stage of development it is difficult to rear
them, and I know of no Stomatopod which has been reared from the egg under observation except
the Bahama Gonodactylus chiragra. As the pelagic larvee are large and conspicuous they are
often captured at the surface of the ocean in the tow net, and the number of genera and species of
Stomatopod larve which have been described is nearly equal to the number of adult species which
are known, and the opportunity to identify even one of these larve by actually rearing it from the
egg is a most noteworthy and important occasion.

The habits of the Bahama Gonodactylus afford this opportunity ; for the nature of the rock
which it inhabits prevents the construction of a deep burrow, and as the fragments of rock may
easily be carried ashore and broken up the eggs can be obtained without difficulty. At the time
of my first visit to the Bahamas I was engaged in correcting the proofs of my report on the Chal-
lenger Stomatopods, and one of the motives of the expedition was the hope that I might possibly
obtain Stomatopod eggs. A day or two after our arrival Dr. E. A. Andrews brought me a Gono-
dactylus and a bunch of yellow eggs, which he had picked out of a rock which he had broken to
pieces while searching for Annelids. The eggs were newly laid, and, while they were obviously
those of some crustacean, there was no evidence that they belonged to Gonodactylus except the
fact that they were found among the fragments of a rock which also contained this apimal. As
soon as I saw the eggs and heard how they had been obtained I started for a point where the
beach was covered with fragments of coral rock. It was then late in the afternoon and growing
dark, but I waded into the water and carried ashore as large a rock as I could lift. After I had
thrown this on to a larger rock and broken it to pieces there was just daylight enough to show me

356 MEMOIRS OF THE NATIONAL AGADEMY OF SCIENCES.

(

the Gonodactyli scattering in all directions, and the masses of yellow eggs which were spattered
over the large rock which I had used as an anvil; but the problem was solved, and I went home
and to bed, confident that I should next day get all the embryological material I needed.

As shown in PI. 11, the animal molds or shapes the mass of eggs into a hemispherical cap,
which fits over the convexity of the hind body and lies between it and the stone wall of the bur-
row. The parent reaches out to snatch at passing prey, but so long as she is undisturbed she
remains in the burrow. When the burrow is broken open she quickly rolls the eggs into a ball,
folds them under her body in a big armfal, between the large joints of her raptorial claws, and
endeavors to escape with them to a place of safety. The promptness with which this action is per-
formed would seem to indicate that it is an instinet which has been acquired to meet some danger
which frequently presents itself. It would seem as if a cave in a solid rock were a pretty safe
refuge from all enemies except a naturalist with a geological hammer, and it is difficult to say
what the accident is which has thus been provided against. The larger beads of growing coral
are often broken off by the waves, and loose fragments of rock are overturned by severe storms,
and it is possible that, when alarmed by a violent shock, it flees from its cave to escape the
danger of being crushed when the rock is torn from its place and turned over. At any rate its
habit is the reverse of that of most burrowing animals, for they usually retreat to the depths of
the burrow when alarmed. This is true of all the Stomatopods which I have had an opportunity
to observe except this species, and the chief use of the burrow of Squilla empusa is for refuge in
danger, while Lysiosquilla excavatrix darts down its burrow at the least poe and can not be
driven out even when the sand has been dug up on all sides of it.

THE METAMORPHOSIS OF GONODACTYLUS CHIRAGRA.

That feature of the life of Stomatopods upon which new data are most to be desired is the
history of the early larval stages, and an abundant supply of the eggs of Gonodactylus chiragra
rendered it an easy matter to obtain this history for that species. I also obtained a complete series

of eggs for studying the embryology, but, as a few preliminary sections showed that this was of

slight interest and that there is no essential difference from other Macroura as regards the egg
embryology, this subject was not studied.

Most of our knowledge of the metamorphosis of Stomatopods is based upon the comparative
study of collections of alcoholic specimens, and the direct observations on living larve are very
seanty. In 1882 Faxen published an account (Selections from Embryological Monographs com-
piled by Alexander Agassiz, Walter Faxon, and E. L. Mark, I Crustacea, Cambridge, 1852, Bull.
Mus. Comp. Zool., Vol. 1x, No. 1, Pl. vin, Figs. 2 and 3) of observations made three years before
upon a young Squilla empusa which he had reared from an Alima larva; and in a paper which
was published in 1879 I described (On the larval stages of Squilla empusa) a series of similar larvze
which I had studied while they were alive, and which was sutliciently complete to warrant the
statement that they were the young of Squilia empusa, and that this species probably hatches from
the egg in the Alima stage. In my report on the Challenger Stomatopods (Report of the Scientific
Results of the Voyage of H. M. S. Challenger during the years i873~76, xv1, part XLV, 1886) I
have given an account of the metamorphosis of Lysiosquilla excavatrix which I had reared at
3eautfort, N. C.: but except for these observations our knowledge of Stomatopod metamorphosis
rests upon the Comparative study of preserved specimens, and, while the series which are picked
out from miscellaneous collections sometimes present pretty satisfactory evidence as to the adults
which they represent, this sort of indirect evidence can not be conclusive.

Large and varied collections of larvie have been compared for the purpose of selecting those
which form stages in the same series, and of ascertaining as accurately as possible the adult aftini-
ties of theoldest larvie, by Claus (Die Metamorphosen der Squilliden, Abhandl. d. k. Gesellsch. d.
Wiss., Gottingen, Bd. xvi, pp. 1-55, Pls. I-vm11, 1871) aud myself (Challenger Rep., pp. 81-114). My
own report was, so far as this subject goes, a supplement to Claus’s work, for in its preparation I
availed myself of his methods and results, amplifying and completing many of his observations,
and confirming some of his results and correcting others. Combining his work with my own, I
devoted a chapter of my report to the discussion of the larve, and gave a scheme or outline of
the probable metamorphosis of each genus of adult Stomatopods. =

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 357

Stomatopod larvee or Hrichthidw, as they were named before their larval nature was suspected,
have been divided into four genera, Hrichthoidina, Hrichthus, Squillerichthus, and Alima. Of these
four the first, Hrichthoidina, is simply a younger stage in the life of the Hrichthus, and the third,
Squillerichthus, a tully-grown larva of the Hrichthus type, so that the genera become reduced to
two, Hrichthus and Alima. Of these two genera, one, Alima, is much more sharply defined than
the other, Hrichthus, which contains a number of divergent types, of which I have shown that
five may be clearly distinguished, and I have proposed, for these five, names which indicate the
adulf genus to which each corresponds. I have shown that there are many reasons for believing
that all Alimi are Squilla larvie; Alimerichthus, the larvie of Chloridella; Brichthalima, the larvee
of Coronida; Lysierichthus, the larvee of Lysiosquilla, and Pseuderichthus, the larvie of Pseudo-
squilla. The remaining larval type may be distinguished from the Lysierichthus by the shallow-
ness of its carapace, which is not at all infolded, and by the position of its postero-lateral
spines, which arise very close to the dorsal middle line; while it may be distinguished from the
Pseuderichthus larve by the length of the posterolateral spines, which are at least half as long as
the carapace, and also by the fact that the telson is wider than long and longer than the long
outer spine of the uropod. Tor this larval type, which was represented in the Challenger collec-
tion by many specimens, I proposed the name Gonerichthus, giving, at the same time, many
reasons for regarding it as the larya of the genus Gonodactylus. Several of these larve were
selected and shown in PI. x11, Fig. 5, Pl. xu, Fig. 9, and Pl. xv, Figs. 1 and 5, of my réport; and
I pointed out that in all of these larvie, as in the young Gonodactylus, the sixth abdominal somite
has a pair of submedian spines near its posterior edge, and its posterolateral angles are produced
into acute spines. The telson is slightly wider than long, and its submedian spines are long and
slender, but shorter than they are in Pseuderichthus. The telson is notched on the middle line,
and there are from fourteen to twenty small secondary spinules on its posterior edge, between the
submedians. There is one small secondary spinule internal to the base of the lateral marginal
spine, avother internal to the base of the intermediate,,and a third midway between this and the
submedian.

In Pl. xy, Figs. 5 and 6, of my report, as in the young Gonodactylus, the outer edge of the
proximal joint of the exopodite of the uropod is fringed by nine marginal spines, the terminal one
longest, and the outer spine of the basal prolongation is much longer than the inner, but not so
long as it is in Pseuderichthus. A comparison of the telson of the young Gonodactylus with that
of the other larval types will show that the one now under discussion is the only one which exhibits
this resemblance, and as this larva never exhibits any traces of marginal spines on the dactyle of
the raptorial claw it must pertain to some known adult with an unarmed dactyle or else to a new
genus. It is not probable that a larval type which is so common pertains to an unknown adult
genus. The larve are not Protosquilla, as this genus has the telson fused with the sixth abdom-
inal somite, while it is free in the older larve; nor are they Pseudosquilla, for they have no movable
spinules on the tips of the submedian spines of the telson; and as all the other genera of Stoma-
topods except Gonodactylus have the dactyle armed, the only remaining genus is Gonodactylus,
and the structural characteristics of the oldest larve indicate that they are the young of species
in this genus.

Led by these considerations I did not hesitate to speak of these larve, in the Challenger
report, as Gonerichthi, or young Gonodactyli, and to give this larval form as one of the diagnostic
characteristics of the genus. This determination rests, however, upon circumstantial or indirect
evidence; and, while the evidence is quite conclusive, I was nevertheless pleased to obtain more
positive proof from the larvie which I reared from the eggs of Gonodactylus chiragra.

Like many other Crustacea which inhabit the coral reefs, this species has its metamorphosis
abbreviated and it hatches from the egg in an advanced condition. It is shown just before hatching,
seen from behind in PI. xtv, Fig. 1, and from in front in Fig. 2. The large yolk covers the dorsal
surface, and the larva is doubled on itself, so that the telson and the tip of the abdomen are visible
in a front view. The first five abdominal somites are indicated before it leaves the egg, and the
first five pairs of abdominal appendages are fully developed, although the other appendages, with
the exception of the mandibles and the large raptorial second maxillipeds, are either absent or rudi-
mentary, The eyes are large, and even before hatching they are movable, although they are
nearly sessile. : \

3958 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

The larva, immediately after hatching, is shown in side view in Pl. xrv, Fig. 3; in ventral view
in Pl. xv. Fig. 8, and in dorsal view in Fig. 7 of the same plate. The carapace is nearly half as
long as the entire animal, and its posterior border, which is deeply emarginated, crosses the midde
line over the posterior edge of the tenth somite; the somite which carries the appendages which
are usually called, in the decapod Crustacean, the second pair of legs. There is a short, rather
stout rostrum, and the anterior end of the carapace, which covers about half the eyes, is nearly
semicircular. The posterolateral spines are short and curved outwards; there are no secondary
spines external] to their bases, but there is a small median dorsal spine on the posterior edge of the
carapace, while the anterolaterals are absent. The antennule consists of a two-jointed shaft with
two flagella, one terminal and the other arising from the dorsal surface of the distal joint of the
shaft. The antenna consists of a rudimentary exopodite, which is cylindrical and ends in five
swimming hairs, although it is of little use in locomotion. The large eyes are subspherieal,
nearly sessile, and they touch each other on the middle line dorsal to the antennules. The man-
dibles are enormous and the two pairs of maxilla rudimentary, as are also the first pair of maxil-
lipeds, while the second pair, the large raptorial limbs of the adult, are well developed, although

the dactyle is not folded backwards upon the penultimate joint or propodite. The third, fourth,

and fifth maxillipeds, corresponding to the third maxillipeds and first and second ambulatory
limbs of decapods, are rudimentary, and the three following appendages are absent, although all
the corresponding somites are indicated as well as their ganglia. The abdomen is abont twice as
wide as the thoracic region and somewhat more than half as wide as the carapace... The first five
somites are distinct and all end in acute posterolateral angles. The suture which separates the fifth
from the unsegmented region, which represents the sixth and the telson, is obscure, and this
region is longer than wide.

The abdominal appendages gradually decrease in size from the first and largest to the fifth
pair, but all have their adult structure, except that they,carry no gills and all are functional.
The telson has four marginal spines on each side. Its posterior edge is slightly notched and ear-
ries Seven or eight pairs of minute movable spines. The newly hatched larvze swim actively about
by meaus of their abdominal feet, not by flexing and extending the abdomen, and notwithstand-
ing the presence of a great mass of food yolk in the walls of the stomach they eat voraciously.
By a lucky chance I found their proper food at once, Several bunches of the eggs of some
unknown Nudibranch were in the aquarium in which the first brood hatched, and the larve, nearly
a thousand in all, soon settled down upon them, covering them completely, and at once began
tearing them off and eativg them. When washed away from them by means of a jet of water they
swam about the aquarium for a short time, but soon settled down upon the eggs again. As these
eggs are not very abundant they can hardly be the only food of the young larvze, although I could
find nothing else that they would touch, and they refused the eggs of ali other Nudibranchs. At
this stage the heart consists of a large anterior chamber in the region of the second maxillipeds
and a large dorsal vessel running as far as the fifth abdominal somite, with a pair of ostia in each
somite.

After about sixty hours they moulted and assumed the form which is shown in side view in Pl.
xiv, Fig.4. The rostrum and the spines on the posterior border of the carapace have lengthened,
but its shape and relative size are about as before. The second antenne are more clearly divided
than before into a shaft and a scale, which has lost its hairs and is more flattened. The first pair
of maxillipeds have made their appearance in the adult form, and the second pair are much larger
than before, and the dactyle is now folded back onto the edge of the flattened penultimate joint. In
all other respects the larva is like the younger one, but a little longer and with less food yolk. In
about a week after hatching they molted again and passed into the third (Erichthus) stage, which
is Shown from above in PI. xv, Fig. 9, and in side view in Pl. xtv, Fig. 5. The rostrum is now greatly
elongated and reaches to the tips of the antennules. Small anterolateral spines have made their
appearance, as weil as a small spine external to the base of each posterolateral. These latter are
greatly elongated and very slightly divergent. A great change in the shape of the carapace has
taken place, as will be seen by comparing Fig. 7 of Pl. xv with Fig. 9. Its lateral margins are
nearly parallel, and its greatest width only a little exceeds that of the abdomen. Its posterior
border is now nearly transverse and crosses the middle line above the last thoracic somite. -The

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 359

sixth abdominal somite has separated from the telson, but its appendages are not yet developed.
The seale of the antenna is now fringed with hairs, and the eyes are divergent, with well devel-
oped stalks. The raptorial claws have greatly increased in size and are beginning to approximate
to the adult form, while at the earlier stage they closely resembled the chel of the third, fourth,
and fifth pairs of maxillipeds of an adult Stomatopod. From this time on to the end of its larval
life the young Erichthus of Gonodactylus chiragra presents the characteristics of that larval type
for which I have proposed the provisioual name Gonerichthus; and, while the resemblance grows
stronger as the larva grows older, it is unmistakable even now, and still clearer after the next molt,
when it assumes the form shown in PI. xtv, Fig. 6, from above, and obliquely from below in PI. xv,
Fig. 10.

The antennulary flagella are now beginning to elongate, and that of the antenna is now rep-
resented by a bud, but there are no new appendages, although the sixth abdominal somite is now
indicated. Although it is very much younger than the Gonerichthi shown in my Challenger report
in Pl. xv, Figs. 1, 5, 6, and 11, it resembles these larvee in the following features as well as in
many minor points: The rostrum is long and reaches beyond the tips of the antennules, and it has
four or five median teeth on its ventral surface. The anterolateral angles of the carapace end in
acute spines pointing forwards, and the anterior edges are inclined towards each other, so as to make
at the base of the rostrum an angle alittle greater than a right angle. The lateral borders of the
carapace are nearly parallel, and the posterolateral spines long, slightly divergent, and with a
small acute spine external to the base of each. The carapace covers all the five thoracic somites
and all or nearly all of the first abdominal, and its posterior border is transverse. The median
dorsal spine, which was carried on the posterior edge of the carapace of the younger larve (Figs. 3,
4, and 5 of Pl. xiv), has disappeared, althouga it persists until a much later stage in the larve
shown in Figs. 1,6, and 11 of the Challenger report. The hind body is now nearly three-fourths
as wide as the carapace.

The lateral margins of the telson still carry, as they did during the earlier stages, four nearly
equal marginal spines on each side; of these the most anterior is the external, the next the inter-
mediate, the third a secondary spinule, and the fourth, which, at the stage shown in Fig. 6, Pl. xtv,
forms the posterolateral angle of the telson, is the submedian. The posterior border between the
submedians is very slightly notched and nearly transverse. All the Challenger Gonerichthi are
very much older than this larva, and their telsons are more developed. The spines especially are

- much more elongated; but in Figs. 5 and 6 of Pl. xv of the report the secondary spine can be

clearly recognized about halfway between the submedian and the intermediate.

With the assumption of the form shown in Pl. xv, Fig. 10, the habits of the larva undergo a
sudden change. Up to this time, while able to swim briskly about by the use of their abdom-
inal appendages, they spent most of their time near the bottom of the aquarium, seldom going
up more than an inch or two, although they are quite able to reach the top of the water, which
was about 10 inches deep, and when masses of Nudibranch eggs were suspended near the surface
of the water they quickly discovered and fastened upon them.

Up to this time, also, they were peaceful and did not attack each other. Several hundred sur-
vived the molt which precedes the beginning of their pelagic life, but all of them soon died and none
passed this stage, which is the one shown in Fig. 10. They now left the bottom, and became rest
less, swimming continually at all levels in the water. They refused to touch the eggs of which up to
this time they had been so fond, and I could find nothing else which suited their appetites, but their
proper food is, beyond question, small swimming animals of some sort, for they now began fighting
among themselves, and when two met they would seize each other with their raptorial claws, and
then tumble over and over together, until they struck the bottom, when both died. The survivors
would not touch the dead bodies, although most of them soon shared the same fate, and the rest
became weak and soon died. ;

At the same time that I was studying the growth of the captive larvee I captured several older
ones in the surface net, and one of them somewhat older than Fig. 10 is shown in Figs. 11 and 12.

‘The third, fourth, and fifth maxillipeds are now developed and are like those of the adult; and

360 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

the three pairs of free thoracic legs, and the uropods are represented by buds. An umber of moults
and probably an interval of many weeks intervenes between this stage and the one shown in Pl. xv,
Fig. 11 of the Challenger report.

The life history of this species of Gonodactylus, in the Bahama Islands at least, is thus seen
to be extremely simple. It hatches as an Erichthus and remains an Erichthus until it assumes its
adult form ; and as the successive appendages make their appearance they have from the first the
structure which they are to retain through life. The statement which I made in my Challenger
report (p. 55), that Gonodactylus hatches from the egg in the Hrichthoidina stage and subsequently
changes into an Erichthus, is an error, at least so far as Gonodactylus chiragra is concerned,
although it is possible, in view of the great variation which we have observed in a single species
of Alpheus, that in other regions, where the adults have different habits, the larva may batch ina
younger stage. Coral-dwelling crustacea seem to exhibit a tendency towards the abridgment of
their metamorphosis, and it is not at all improbable that other species of Gonodactylus may have
an Erichthoidina stage. ¢ 5

The Challenger collection contains a bottle of very minute and young larvee in the Erichthoi-
dina stage, and one of these is shown in Fig. 3 of Pl. x11 of my report. Comparison between this
and the newly hatched Erichthus of our species, PJ. xiv, Fig. 3, will show many points of resem-
blance, and future research may possibly prove that it is the larva of Gonodactylus, although the
statement that all Gonodactyli hatch as Erichthoidine is an error.

CHAPTER) LV.

THE METAMORPHOSIS OF ALPHEUS,

By W. K. Brook anp F. H. HERRICK.

(With Pls, I, II, IV, XVI to XXIV. )
Section I.—THE METAMORPHOSIS OF ALPHEUS MINOR FROM BEAUFORT, NoRTH CAROLINA.

This small species is found in abundance at Beaufort, North Carolina, andin the Bahama Islands,
and itis no doubt widely distributed along our southern coast. At Beaufortitis found in shallow
vertical burrows in the sandy mud which forms the bottom of most of the land-locked sounds
between tide marks. It is also met occasionally in shells, and under loose stones and oyster
shells.

During its development, between the time when it hatches from the egg and the time when it
acquires the adult form, it passes through a long metamorphosis, divided into many stages. Its
life history has been traced by one of the authors at Beaufort, and by the other at Nassau, and the
individuals from both these localities pass through exactly the same series of changes. As we
also find that other species, such as Alpheus normani, pass through the same metamorphosis, the
life history of Alpheus minor may be regarded at the primitive or ancestral life history of the
genus, which originally characterized all the species; although it is now retained in its perfect form
by only a few, and has undergone secondary or recent modifications in the others.

THE FIRST AND SECOND LARVAL STAGES.

The stage in which the larva hatches from the egg is of very short duration, as it molts and
passes into the second stage within a few hours after hatching. No drawings of it were made
before the change, but this is very slight, and the description of the second stage holds true in all
essentials of the first stage, except that the tips of the exopodites of the three pairs of maxillipeds,
and the plumose hairs on the antennules and antenn:e are not fully extended until after the change.

The second larval stage is shown in PI. xvi, Fig. 2, and in Pl. xvu, Fig. 2, and various organs of
the larva during the first stage are shown in Pl. xv1, Figs. 4, 6,7, and 8, and Pl. xvi, Fig. 4. In
Pl. xvi, Fig. 4, is the antenna of the first larval stage, Fig. 6, the first maxilla, Fig. 7, the second
maxilla, Fig. 8, the mandible, and Fig. 4 of Pl. xviu, the first maxilliped. As shown in Pl. xvu,
Fig. 2, and in Pl. xvt, Fig. 2, the locomotor organs of the larva during the first and second stage
are the plumose exopodites of the antennz and of the three pairs of maxillipeds. There are no
functional appendages posterior to the maxillipeds, and the large eyes are freely movable and
entirely uncovered. :

The larva has all its appendages fully developed and functional as far back as the third pair of
maxillipeds. Following these are three bud-like rudiments of the first, second, and fifth pairs of
thoracic limbs, and posterior to these a long tapering abdomen, divided into six segments, there
being at this time no joint between the telson and the sixth abdominal segment. During the first

361

362 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

stage there are no traces of any abdominal appendages, but in the second stage, the outlines of
the sixth pair are faintly visible under the cuticle of the telson, as shown in PI. xvI, Fig. 2.
The stomach is almost completely free from yolk, and the surface of the body is marked ‘by
red and yellow pigment spots, which are very constant in position and number, and are well shown
in the figures. :

As shown in Pl]. xvi, Fig. 2, the antennule consists of a stout shaft composed of a long basal
portion with no trace of an ear and a much shorter distal joint, which Carries externally a much
shorter and smaller joint with four sensory hairs, and internally a long slender plumose hair, which
is not fully extended until after the first moult. At this stage this hair is almost sessile upon the
shaft, although its base is destined to give rise to the long flabellum of the antennule of the
adult.

The antenna has a large exopodite, which is fringed with plumose hairs, and is an efficient
organ of locomotion. During the first larval stage this exopodite, which is destined to become
the flat scale of the adult antenna, is cylindrical and distinctly annulated, as shown in PI. xvi, Fig:
4. At this stage it is divided into a basal portion and five movable joints, about equal in total
length to the basal portion. After the first molt the annulations become less distinct, although
the “scale” is still eyligdrical, as shown in Pl. xvi, Fig. 2, The basal joint of the antenna is about
equal in length to the “scale,” undivided, and it carries upon the inner edge of its-distal extremity
a small, short, movable joint, with a single, long, plumose hair, which is “telescoped” before the
first moult, but fully extended afterwards. This short joint is the rudimentary antennal fla-
gellum, which in the adult is equal in length to the entire body of the animal.

The mandible is shown in Fig. 8. It is deeply cleft into two branches, the outer one with two
rows of large, strongly marked dentations, and the inner one with a rudimentary palpus, two rows
of hairs, and a finely serrated cutting edge. The first maxilla is very small, but it does not appear
to be rudimentary. It is shown in Pl. xvi, Fig. 6. No exopodite could be made out. There is
a small endopodite, with one long, plumose hair, and two basal joints, one with two sharp cutting

hairs and the other with one. The second maxilla is shown in PI. xvi, Fig. 7. The two basal”

joints are feebly indicated, and each carries three slender, simple hairs. The endopodite carries
two terminal hairs, and the flat exopodite is fringed by seven. I could not determine whether
these hairs are plumose or not. The three pairs of maxillipeds are functional and they present
features which are characteristic of the genus Alpheus (see Pl. xv1,Fig. 2). Each has a large,
flattened, polygonal, basal joint, which carries upon its inner edge a few short, sharp teeth, and
upon its outer edge a long, flat exopedite, with plumose swimming hairs, and an endopodite
which presents several peculiar features.

The endopodite of the first maxilliped is very short and two-jointed, that of the second is
somewhat longer and five-jointed, while that of the third is very greatly elongated, without traces
of joints, and ending in a long, simple hair which, as shown in PI. xviu, Fig. 4, is telescoped before
the first moult, but immediately afterwards becomes lengthened, as shown in PI. xv1, Fig. 2, until
it reaches forward beyond the tips of the antennules and antenne. Following the maxillipeds are
three pairs of buds to represent the first, second, and fifth pairs of thoracic limbs. The first bud
consists of a single branch, which is shown by its subsequent history to be the exopodite. The
second has two branches, a short exopodite, and an extremely short endopodite, while the third
consists of a somewhat longer, but still rudimentary, shaft, which represents the endopodite of
the fifth thoracic limb, and has no trace of an exopodite,

The hind body is divided by joints into five abdominal somites, behind which is a long und1-
vided region to represent the sixth abdominal somite and the telson. Before the first moult none
of the abdominal appendages are present, but after this molt the sixth pair are faintly indicated
under the integument of the telson, as shown in PI. xvi, Fig. 2. The telson itself is broad, sub-
triangular, with its posterior border nearly straight and transverse. It carries eight pairs of stout
plumose hairs, of which three pairs are much longer than any of the others and nearly equal.
This set of three spines is placed at the angle of the posterior edge on a lobe or elongation, which,
while it is so slightly marked as to scarcely interrupt the triangular outline, is still very distinct
and easily recognizable. Of the remaining five spines on each side of the middle iine, one is on
the external border, and the other four on the posterior edge between the group of three and the
middle line. The internal one is very small and might easily be overlooked.

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MEMOIRS OF THE } tet gota ACADEMY OF SCIENCES. 363

=

THE THIRD LARVAL STAGE.
(PI. xvi, Fig. 1.)

After molting the second time the larva assumes the form shown in Pl. xvt, Fig. 1. It is also
shown, much less enlarged, in side view in Pl. xvi, Fig. 1. The first and fifth thoracie limbs are
now functional, the second is represented by a bud, all the abdominal somites are distinct, and
the sixth abdominal appendage has made its appearance. The first five abdominal appendages
are still unrepresented, and the endopodite of the sixth is rudimentary, although its exopodite is
fully developed and functional.

Those appendages which were presentin stage two have undergone little change. The external
branch of the antennule has, in place of the four sense-hairs of the earlier stage, only two, which
are much longer than before. The long terminal hair of the inner branch has lost the marginai
hairs of the earlier stage and is now simple, while two plumose hairs have made their appearance
on the lower surface of the distal joint of the shaft. The scale of the antenna is still cylindrical,
but the annulations which marked it during the earlier stage have disappeared. The flagellum
still consists of only one short joint, and the long terminal hair which it carried at the earlier stage
has disappeared. The mandibles, maxille, and maxillipeds are about as they were before, but the
endopodite of the third mhescllipad has almost completely lost the long terminal hair of stage
two, and has also become relatively shorter, and is now divided into four joints.

The first thoracic leg, which was rudimentary in stage two, has now acquired a flat basal
joint and a plumose exopodite, like those of the preceding appendages, but the endopodite is
represented only by a rudimentary knob or bud upon the anterior edge of the basal joint. The
second thoracic limb is, as it was at the earlier stage, a two-lobed bud. No buds have as yet
appeared between it and the base of the fifth thoracic appendage, which is now fully developed
and forms the most conspicuous peculiarity of this stage in the development of Alpheus. It has
no exopodite, its basal joint is not enlarged nor flattened, and its long, slender, cylindrical shaft,
made up at this stage of four joints, is prolonged at its tip into a long, slender, tapering, simple
hair, the end of which reaches beyond the tips of the antenne when the appendage is in the posi-
tion shewn in the figure Pl. xvi, Fig. 1. The appendage seems to have little power of motion and
it seldom deviates much trom the position shown in the drawing, being usually carried closely
pressed against the ventral surface of the body between the bases of the other appendages, with
its tip directed forward. All six abdominal somites are distinct and movable, but the first five
have as yet no traces of appendages. The first four somites are short and equal, the fifth 1s nearly
as long as the first four together, and the sixth is very narrow and almost twice as long as the
fifth. The endopodite of the sixth abdominal appendage is present and of considerable size, but
it is not as yet functional, although the exopodite, which is not very much larger, is fringed by
six long, plumose, swimming hairs and is used in locomotion. The two spines which are carried
upon the lateral margins of the telson at an earlier stage have disappeared, and there is less dif-
ference than before in the relative sizes of the others, but the general form is the same.

FOURTH LARVAL STAGE.

The subsequent history of Alpheus minor was traced by one of the authors-at Beaufort and
by the other at Nassau, but as the stages which follow were found to be almost exactly like the
corresponding stage of other species which had already been drawn, 1t did not seem to be advisa-
ble to make new figures, and in the remainder of the description the illustrations which are
referred to actually represent the larvie of other species. After its third molt the larva of
Alpheus minor passes into its fourth stage, when it becomes almost exactly like the fourth. larval
stage of Alpheus heterochelis, shown in Pl. xvii, Fig. 3. There is little change at the anterior end
of the body, except that the carapace now begins to extend over the eyes, and the ears have made
their appearance in the basal joints of the antennules. The mandible has lost its outer branch,
and the basal joint of the second maxilla, P). xy1, Fig. 5, carries on its inner edge three hairy lobes.
There are now five pairs of swimming appendages in place of the three of stages one and two, and
the four of stage three. ‘These five are the exopodites of the first, second, and third maxillipeds

364 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

=

and those of the first and second thoracic legs. The endopodites of the maxillipeds are as befcre.
The endopodite of the first thoracic leg, which was represented in stage three by a rudimentary
bud, now appears to be entirely wanting. The second thoracic limb, which in stage three was :
represented by a bilobed bud, now consists of a basal joint, with a large, functional, plumose
exopodite and a rudimentary, bud-like endopodite. Between this appendage and the base of the |
fully developed fifth thoracic limb there is a row of buds to represent the third and fourth thoracic

limbs, which became developed after the next molt. The fifth is about as it was in the preceding

stage, and it carries no trace of an exopodite. The abdomen is about as before, except that the

endopodite of the sixth abdominal appendage, the only one yet represented, is now fully devel-

oped and fringed like the exopodite by long, plumose, swimming hairs. The telson has become

elongated and narrow, and the spines upon its posterior end are much smaller than before.

THE FIFTH LARVAL STAGE.

None of the figures of the larve of other species exactly represent the larva of Alpheus minor
after the next molt. The eyes are now partially covered by the carapace, and the swimming
organs are the seven pairs of fully developed exopodites belonging to the three pairs of maxillipeds
and the first four pairs of thoracic legs. At this stage these four pairs of appendages reacquire
their endopodites, and the anterior end of the body is similar to that of the larva shown in PI. Xx1,
Fig. 1, from which, however, it differs greatly as regards the telson and the sixth abdominal ap-
pendage. The first five abdominal appendages are now represented by buds like those shown in
Pl. xx1, Fig. 1, and in Pl. x1x, Figs. 1 and 2, but the terminal portion of the abdomen is nearly like
that of Fig.3 in Pl. xx. The telson is greatly elongated, narrow, and its terminal spines are
very small.

THE OLDER LARVAL STAGES OF ALPHEUS MINOR.

During the successive molts the abdominal appendages become fully developed, the eyes be-
come completely covered by the anterior edge of the carapace, the antennz become elongated, the
antennule develops a scale, the swimming exopodites of the maxillipeds and thoracie legs disap-
pear, these appendages assume their adult form, and acquire gills, and the animal gradually be-
comes like the one shown in Pl. xx, Fig. 2, which is a young Alpheus of another species. _

THE METAMORPHOSIS OF ALPHEUS HETEROCHELIS FROM THE BAHAMA ISLANDS.

In the Bahama Islands this species passes through a series of stages which, except for a few
minor differences of detail, are exactly like those in the life history which has just been described.

This fact is remarkable when it is known that the life history of the same species is very
different at Beaufort, North Carolina, and that Packard has described still another life history
for specimens of the same species which he studied at Key West.

FIRST LARVAL STAGE.

The Bahama specimens hatch from the egg in the stage shown in side view in Fig. 1 of Pl. xv1ir.
As this larva agrees in all details of its structure with the first stage of Alpheus minor shown in
Pl. xv, Fig. 2, already described, no further description is necessary.

THE SECOND LARVAL STAGE.

Like Alpheus minus the Bahama specimens of Alpheus heterochelis molt within a few hours
after hatching, but they undergo no essential change, and Pl. xv1, Fig. 2, exhibits all the essential
characteristics, although this figure was drawn from a specimen of Alpheus minor.

The most noteworthy specific difference is in the relative length of the marginal spines of the
telson. In the first and second larval stages of both species there are eight pairs of spines, one
pair on the outer edge and seven on the posterior edge, as shown for Alpheus minor in PI. xvi, Fig. 2,
and for Alpheus heterochelis in P|. xvi, Fig. 3. In both species the pair next the median line are
rudimentary and the next pair very small, but the three which arise from the rounded angle of the

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 365

telson are much more nearly equal to the others in Alpheus heterochelis than in Alpheus minor. If,
as seems probable, the triangular telson of the macrouran zoéa is a secondary modification of the
deeply furcated telson of a more ancient protozoea, then the first larval stages of Alpheus minor
are in this respect more primitive or protozoean than those of Alpheus heterochelis.

THE THIRD LARVAL STAGE.

This is shown from below in PI. xv, Fig. g; and a comparison with Fig. 1 of Pl. xv1 will show its
very close resemblance to Alpheus minus at the same stage. The only essential difference between
them relates to the rudimentary thoracic limbs. In both species the first thoracic limb has a
functional swimming exopodite and a rudimentary endopodite, and in both the fifth thoracic limb
has a greatly elongated jointed cylindrical endopodite and no exopodite, but between these limbs
Alpheus heterochelis has buds to represent the other three pairs of thoracic limbs, while Alpheus
minor has buds for only one pair, and the other buds do not appear until after the next molt.

THE FOURTH LARVAL STAGE OF ALPHEUS HETEROCHELIS.

This is shown from below in Pl. xv, Fig. 3, and there are no noteworthy differences between
it and Alpheus minor.

THE LATER STAGES OF THE BAHAMA ALPHEUS HETEROCHELIS.

The transformation of the larva into the adult Alpheus occupies a number of molts, and the
general character of the changes will be understood by the study of Pl. x1x and xx, although
these plates were drawn from Beaufort specimens of the species.

THE METAMORPHOSIS OF ALPHEUS HETEROCHELIS FROM BEAUFORT, NORTH CAROLINA.

As shown in PI. xx, Fig. 1, this, before it hatches from the egg, reaches a stage of develop-
ment which somewhat resembles stages two and three of the Bahama specimens. There are many
important differences however, and the stage in which it hatches is not directly comparable with
any stage in the life of the Bahama form, nor in that of Aipheus minor. Just before hatching it
has, like the Bahama form immediately after hatching, three pairs of fully developed swimming
maxillipeds, but it also has buds to represent all five pairs of thoracic legs. The antennary scale
and flagellum are much more advanced than they are at a much later stage in the Bahama form,
and the abdomen is much more distinctly segmented. The larva, immediately after hatching, 1s
shown in side view in Pl. xrx, Fig. 2, and in ventral view in Fig. 1. The antennule and antenna
are shown on a larger scale in Figs. 3 and 4, and the mandible and first and second maxillw in
Figs. 5, 6, and 7 of the same plate. The animal now has all the appendages which are present in
the adult, but all behind the maxillipeds are rudimentary, although they all become functional
after the first molt, as shown in Pl]. xx, Fig. 3.

The antennule, Pl]. x1x, Fig. 3, has a long cylindrical shaft made up of three joints fringed
with plumose hairs and terminating in an exopodite with sensory hairs and an endopodite or
flagellum, which is short and rudimentary but much longer than it is in the younger stages of the
Bahama specimens. The antenna, Fig. 4, presents even greater differences. The flagellum is
about as long as the scale, and two jointed, while the scale itself is flat, although its tip still pre-
sents traces of a primitive segmented condition. It is, however, of little use in swimming, and in
fact the larva has at this stage only very feeble locomotive power. The eyes are stalked and
movable and almost completely uncovered. The mandible is simple and without a palpus, as
shown in Fig. 5. The first maxilla, Fig. 6, is very small, but apparently it is not rudimentary as
its two lobes carry cutting hairs. The second maxilla, Fig. 7, is a broad flat plate, very much
more developed than that of the newly hatched Bahama specimen shown in PI. xvi, Fig. 5.

The three pairs of maxillipeds (Pl. x1x, Fig. 1) are almost exactly like those of the newly
hatched Bahama larva (PI. xvut, Fig. 1) or those of the Alpheus minor at the same stage (Pl. XVI,
Fig. 2), but the thoracic appendages (PI. x1x, Fig. 1) are entirely different, and the ventral surface
of the body is covered by a mass of limbs closely crowded, all pretty well developed, but all as yet

SOE Se —_ ae a .

566 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.
funectionless. Careful examination shows that there are five pairs (the five pairs of thoracic limbs),
and that all but the last pair are biramous. In all, the exopodites are longer than the endopodites,
which decrease in length from in front backwards, while the endopodites increase in length. The
later history of these limbs shows that the exopodites never become functional, as they do in the
Bahama form, °

All six abdominal somites are distinct, although the line separating the sixth from the telson
is faintly marked. The first five pairs of abdominal feet are represented by five biramous buds

projecting beyond the outline of the body, while the sixth pair are only faintly outlined under the:

cuticle of the telson, which itself presents a most important difference from that of the young
Bahama larva, as it is not triangular, but spatulate; and of the eight pairs of setze the three pairs
whieh in Alpheus minor lie on the lobe at the angle of the telson are not on a distinct lobe, nor do
they differ in size from the adjacent sete.

This larva molts a few hours after hatching, and at once undergoes the most profound changes,
and assumes the form shown in Pl. xx, Fig. 3. Itis no longer a larva, but a young Alpheus.
The eyes are almost covered by the carapace, the ear is well developed, and all the appendages are
present and functional and essentially like those of the adult. The antennule bas two flagella, each
with several joints. The flagellum of the antenna is more than twice as long as the scale and is
composed of twenty-two joints, while the scale has its final form.

The first maxilla (Fig. 5) has a large club-shaped lobe, fringed with short hairs, and a rudi-
mentary endopodite, while the second maxilla (Fig. 6) is a broad flat plate with cutting lobes and a
short, rod-like endopodite. The three pairs of maxillipeds (Figs. 7, 5, and 9) have assumed the char-
acteristic Macrouran form and are no longer concerned in locomotion, while the thoracic limbs have
elongated into the five pairs of ambulatory appendages of the adult, although they still retain
their rudimentary exopodites. The abdomen is now like that of the adult, and the telson (Fig.
4) islongand narrow. An older specimen is shown in Fig, 2 and a still older one in PI. xvii, Vig. 3.

Comparing the history of the Bahama form with that of the North Carolina form, the most
conspicuous peculiarity, and that which first attracts attention, is the great abbreviation of the
latter. The Beaufort specimens hatch in a much more advanced condition than the Bahama speci-
mens, aud, while the latter pass through many larval stages, the former quickly assume the adult
form. This is not all, nor is it even the most fundamental difference between them. The develop-
ment of the Beaufort specimens is not simply accelerated; it is profoundly modified, so that ne.
exact parallel can be drawn between any larval stage of the one and a stage of the other. The
statement that the Beaufort specimens pass, before ieaving the egg, through stages which are
exhibited during the free life of the Bahama specimens would do violence to the facts; for the
difference between them is very much more fundamental than this statement would imply. For
example, the Bahama form has at first three, then four, then five, and then seven schizopod feet
with functional swimming exopodites, while the Beaufort form never has more than three. As
regards the thoracic region and the first five abdominal appendages the Beaufort larva, at the time
of hatching (Pl. x1x, Pig. 1), is more advanced than the fourth larval stage of the Bahama form
(Pl. xvint, Fig. 3), while the sixth pair of abdominal appendages are like those of the Bahama form
at the time of hatching (PI. xvi, Fig. 3). In the Bahama form the first and fifth thoracic limbs are
the oldest, and the others appear in succession from in front backwards ; all five pairs make their
appearance together in the Beaufort form. In the Bahama form the sixth pair of abdominal feet
appear before and in the Beaufort form after the others. Many minor differences of the same
general character show that we have to do with profound modification of the life history rather
than with simple acceleration.

THE DEVELOPMENT OF ALPHEUS HETEROCHELIS FROM KEY WEST.

According to Packard’s account the specimens of Alpheus heterochelis which oceur at Key West
differ from those which oceur at Beaufort in about the same way that the latter differ from those
from the Bahamas, as the metamorphosis appears to be entirely absent in the Key West speci-
mens. Packard states that, while still inside the egg, they had all the appendages of the adult
in essentially the adult form. There were five pairs of thoracic legs and the first pair had large

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 367

chelz, and the eyes were nearly sessile. In this case also there seems to be modification as well as
acceleration, as Packard says that there were only five pairs of abdominal feet and that these were
well developed. It may seem to some that the fact that these three forms present such great and
constant differences in development is a reason for regarding them as three distinct species, but,
whether we hold that they belong to one, two, or three species, they will still furnish proof of the
existence of profound modifications in the life histories of adults which have remained almost
exactly alike. :

Careful and minute comparison between adult specimens from Beaufort and Nassau showed
the closest agreement in nearly all particulars (v. Chap. v, Pt. First, Section 11), and it has there-
fore seemed best for us to regard them as belonging to q single species; the more so since our
discovery that different individuals of another species found at Nassau (Alpheus saulcyi) differ from
one another during their larval stages in somewhat the same way that the Beaufort specimens of
heterochelis differ from the Bahama specimens.

Alpheus minor and Alpheus heterochelis are very distinct species. The adults have diverged
from one another so far that one could not possibly be mistaken for the other; yet the life history of
the Bahama heterochelis is so exactly like that of Alpheus minor, both at Beaufort and in the
Bahamas, that the same figures of the early stages will serve for both; for the larval stages of
heterochelis have undergone local modifications, while the adults have remained almost absolutely
unchanged, except as regards the reproductive elements and their product.

SECTION V.—LARVAL DEVELOPMENT OF ALPHEUS SAULCYI.

An egg of Alpheus saulcyi just ready to hatch is shown in Pl. xx1, Fig.5. The large claws are
plainly visible through the transparent shell. The antennz are folded back alongside the body,
while the abdominal and closely packed thoracic appendages are directed forward. The telson
overlaps the head. .

First larva (length, = 735 inch).—Fig. 1 shows the larva as it is just hatched. It belongs to
the variety found in the brown sponges. The various parts may be seen more highly magnified in
Pl. xx, Figs. 4, 6,7,9, and Pl. xx11, Figs. 1-8,12. In both varieties the animal hatched as a schizo-
pod, loosely infolded in a larval skin, but not invariably, as I have noticed that in one or two cases,
where females of the longicarpus with very few, perhaps half a dozen eggs, produced young, the
metamorphosis was completely lost, the larvze being in a stage corresponding to that usually at-
tained after the second molt and represented in Pl. xxi, Fig.8 This is referred to again at
the end of the section.

To return to the first larva (PI. xx1, Fig.1); this is fifteen one-hundredths of an inch long. It
is semi-transparent and colorless, except for spots of characteristic red and yellow pigment sprinkled
freely on the abdomen, the telson, and appendages. Rudimentary gills are present and a remuatt
of unabsorbed green yolk is cOnspicuous in the stomach. The carapace covers the bases of all the
thoracic appendages but the last pair. It is produced forward into a short simple spine, the ros-
trum, which extends between the eyes. There is a rudiment, on either side, of the ocular spines
(Pl. xx, Fig. 6), which soon grow forward and give to the front the characteristic trident shape.
The eyes project forward, only the extreme base of the stalk being covered by the carapace. A
median eye or ocellus is present just below and between the bases of the lateral eye stalks.

Both pairs of antennz are biramous and jointed. The antennules (Fig. 8) consist of a stout
peduncle, a short endopodite, and a shorter bud or outer branch, which bears several bunches of
sensory filaments. The peduncle is composed of three segments, as in the adult; the basal joint
being four times the length of either of the other two, and bearing on its outer side a rudimentary

_ aural scale. The upper margin of each joint carries one or more plumose hairs. The antenne

(Pl. xxu1, Fig. 7) are formed on the adult plan. There is an inner antennal stalk consisting of
two joints, bearing a rudimentary flagellum, and an outer scale or exopodite. The distal margin
of the exopodite is garnished with plumose hairs and carries a short outer spur.

The mandibles (Fig. 12, drawn from a larva after the first moult) are deeply cleft, as in the adult.
The outer branch is dentated at its distal end and carries a palpus. The first maxillie (Ivig. 6,

368 MEMOIRS OF THE NATION AL ACADEMY OF SCIENCES.

shown with more detail in Fig. 3, Pl. xx11) have adult characters. They are biramous. The endo-
podite is stout and toothed at its apex. The more slender outer division bears a short spine
near the distal end. In the second maxillie (Fig. 6, Pl. xx1) the scaphognathite or respiratory
plate is most prominent. This is now composed of an anterior portion, bordered with from six to
twelve long plumose hairs and a posterior, rudimentary, and hairless lobe. The inner division
(endopodite) has the adult form, while the innermost lobes of the adult appendage (PI. xxtv. Fig.
9) are unrepresented.

The maxillipeds are all biramous appendages, and their exopodites are the principal swim-
ming organs. The endopodite of the first pair is short and stout and divided at its tip. That of
the third pair is three-jointed and equa] in length to the exopodite. In the first pair of thoracie
legs (Pl. xxi, Figs. 4 aud 7) the inequality of the chele is very marked, and, as we have alrea‘ly
seen, it is so for some time before hatching. Individuals differ somewhat in this respect. The
articulations of the carpus and meros are distinct. The exopodites of this and of the three suc-
ceeding pairs of thoracic limbs are tipped with rudimentary invaginated hairs. The second pair of
pereiopods (PI. xxu, Fig. 1) are chelate, but the articulations of the carpus are not distinet. The
third pair of pereiopods (Fig. 2) end in “bidentated dactyles and have short exopodites. The
fifth pair are without swimming organs.

All the abdominal appendages are present and functional, excepting the sixth pair. They
have only very short hairs until after the first moult. The first pair (Pl. xxi, Fig. 5) consist
of a larger outer and smaller inner blade. This endopodite remains rudimentary in the adult
male, but nearly equals the exopodite in length in the female, as will be seen by reference to Pl.
XxIv, Figs. 4 and 5. This convenient sexual mark probably appears early, but can not be relied
upon at this stage. The second (Pl. xxv, Fig. +) and three succeeding pairs of pleopods have a
stout base, an outer blade like that of the first pair, and a shorter endopodite which bears on its
inner margin a lobule or palp. The sixth pair, or uropods (PI. xx1, Fig. 9), are not yet free. The
inner and smalier divisions point forward, meeting on the middle line. The telson, which termi-
nates the body, covering the outer uropodal limbs, is a rounded, spatulate plate, with a median notch.
Its free posterior edge is fringed with seven pairs of plumose spines, the first or median pair being
rudimentary, and the next four succeeding pairs long and nearly equal.

"Second larva (length, 48; inch).—The first moult takes place either immediately or very soon
after hatching. The animal as it now appears is shown in PI]. xx1, Fig. 2. The principal external
changes thus produced are the following: (1) The rostram and ocular arches extend farther over
the eyes. (2) Both divisions of the antennules are considerably extended. The flagella of the
antenpe are from three to four times their former size and are articulated into twenty to thirty
rings, the scale still not passing the peduncle. (5) The thoracic appendages have more of the
adult characteristics. The articulations of the carpus of the second pair are distinet. The exo-
podites of the first four pairs are functional, and the last pair has grown forward. (4) The
pleopods presently acquire swimming hairs; the telson plate is free and the uropods are func-
tional for the first time. (5) The last thoracic segment is still uncovered and the eyes are
incompletely hooded.

Third larva (length, about + inch).—The third larva as it appears after the second moult,
which takes place in twenty-five to thirty hours after hatching, is represented in Pl. xx, Fig.
8. It has now the general adult character, and can not be called a larva in the strict sense. At
even this early age the pugnacious instinct is strong, and although only about one-sixth of an
inch long, it snaps audibly the fingers of its large ‘‘hand,” which is carried extended forward. It
also swims on the bottom of the jar in all respects like the adult. Only a few globules of yolk
remain in the stomach. The gills are now quite prominent. They are evidently functional to
some degree, and were so, possibly, at an earlier date. The yellow and red pigment cells have
nearly all disappeared or are temporarily withdrawn from view.

A most prominent change at the second moult is the extension forward of the rostrum and
the ocular spines, which form a hood over each eye. The antennal peduncle surpasses the scale,
and its flagellum nearly equals the carapace in length. As in the adult, the large chele are very
prominent. The exopodites of the thoracic appendages have dwindled to rudiments. The view
of the head of a four-days old Alpheus is shown in Fig. 3, Pl. Xxt.

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 369

The fourth form (after third moult).— When six or seven days old the third moult is passed,
but only slight changes are introduced. The small chela and the inner and outer antenne of this
phase are given in Figs. 9, 10, 16, Pl. xxm. The inner branch of the antennules is still relatively
short; the basal or aural spine extends to nearly the end of the first joint. The bristle-bordered
plate of the antennx has now developed a considerable spine near its outer extremity, a rudiment
of which appears in the first larva (Fig. 7). This represents the squamal spine, to which the plate
is ordinarily attached, in the adult. The spine is here developed from the plate. The latter nray
disappear, as we shall see further on, to be finally regenerated from the base of the spine. The
small chela has the adult form.

The fifth form (after fourth moult).—These animals moulted the fourth time ten days after
hatching. Very little change was apparent, except in size, and beyond this point we did not follow
them. e,

METAMORPHOSIS OF ALPHEUS SAULCYI FURTHER ABBREVIATED.

As was Stated above, the metamorphosis of Alpheus saulcyi may be still further accelerated
so as to practically disappear altogether. This fact is illustrated by a young Alpheus hatched
in a glass dish April 25 (Pig. 17, Pl. xxi). The prawn (var. longicarpus) was taken from a brown
sponge. The eggs, half a dozen in number, were slow in developing. The small chela is shown
in Fig. 15.

This phase corresponds with that usually attained after the second moult (shown in Fig. 8,
Pl. Xx1), with which it corresponds in size and color. All the thoracic and abdominal appendages
have nearly the adult form, the exopodites of the former being rudimentary, as in Fig. 8. The
large chela is most prominent, being nearly as large again as the smaller one. The eyes are partly
hooded, but not so much as the four-day old prawn represented by Fig. 3. The Alpheus had to be
held in a compressorium in order to be drawn, so that the parts are slightly distorted by pressure.
At the time of hatching most of the hairs on the appendages generally are in a rudimentary
condition.

S. Mis. 94.24

. e
7.
ALPHEUS: A STUDY IN THE DEVELOPMENT OF CRUSTACEA.
By Francis H. HERRICK.
CONTENTS. >
Introduction. Part SEcOND—Continued.
Methods. IV. The development of Alpheus—Continued.
Part First: BHighth stage: Nine pairs of appendages present.
I. The habits and color variations of Alpheus. Ninth stage: Eye-pigment formed.
II. Variations in Alpheus heterochelis. Tenth stage: Ganglia of ventral nerve-cord
III. The abbreviated development of Alpheus and its distinct and completely separated from the
relation to the environment. skin.
IV. The adult. Eleventh stage: Embryo about to hatch (Al-
V. Variations from the specific type. pheus heterochelis).
VI. Measurements. Twelfth stage: First larva (Alpheus saulcyi).
VII. The causes and significance of variation in Al- Thirteenth stage: Young Alpheus, four to ten
pheus sauleyi. days old.
ParRT SECOND: V. Notes on the Segmentation of Crustacea.
I. Structure of the first larva of Alpheus sauleyi. VI. Cell Degeneration. f -
Il. The origin of ovarian eggs in Alpheus, Homarus, VII. The Origin and History of Wandering Cells in
and Palinurus. Alpheus.
Ill. Segmentation in Alpheus minus. VIII. The Development of the Nervous System.
IV. The development of Alpheus. IX. The Eyes.
First stage: Segmentation to formation of blas- The median eye of the larva and adult.
toderm. General anatomy of the eye-stalk.
Second stage: Migration of cells from blastoderm Structure of the ommatidium.
to theinterior, The invagination-stage. Arrangement of the ommatidia.
Third stage: Optic disks and ventral plate. The development of the compound eye.
Fourth stage: Thickening of optic disks. Ru- (1) Origin of the optic disk.
diments of appendages. (2) Development of the retina and the
Fifth stage: Rudiments of three pairs of ap- optic ganglion.
pendages. Optic disks closely united by The eye under the influence of light and dark-
transverse cord. Degenerative changes. ness.
Sixth stage: The egg-nauplius. X. Summary of Part Second.
Seventh stage: Seven pairs of appendages XI. References. -
formed. Explanation of figures (accompanying each plate).
[With thirty-eight plates. ] ;
INTRODUCTION. Fa

The observations offered in this memoir were undertaken at Beaufort, North Carolina, in 5
June, 1885, at the Marine Zoological Station of the Johns Hopkins University. But little was
accomplished, however, until the next and following seasons, 1886~87, when I enjoyed the advan-
tages of this laboratory in the Bahama Islands. ~

A part of this memoir was accepted as a thesis for the degree of Ph. D. by the Board of
University Studies of the Johns Hopkins University in May, 1888. :

I take this opportunity of thanking Professor Brooks for his invaluable counsel, aid, and
encouragement from the beginning to the end of the work.

At Nassau, New Providence, during a sojourn of four months (March to July, 1887), I had the
rare opportunity of a making a comparative study of a large number of Crustacea. At least thir-
teen species of Alpheus were discovered on the coral reefs and shores of New Providence, and
in all these the eggs have been obtained, and in nearly all the larve or first zoéas have been hatched
in aquaria. Many of these forms are new or but little known, and when the means of publication

is found it is hoped that their comparative and systematic zodlogy can be fully illustrated.
370 :

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 371

The majority of the decapod Crustacea have a long and complicated metamorphosis. That
in a few forms the early stages are jumped, so that the young hatch in practically the adult condi-
tion, is a remarkable fact, and the discovery of a probable cause for this phenomenon in Alpheus
is one of the most interesting results of that part of our work which deals with the metamorphosis
of the genus. .

The development of Alpheus has never, I believe, been previously studied, excepting the
metamorphosis of the two Beaufort species, so that there is no work of others to refer to, which
bears directly upon our subject. But the literature of the Arthropods is very great, commensurate
indeed with the size of the group. During the progess of this work a number of important papers
have appeared which are referred to either in the text or in notes. While much is known of the
Arthropods as a whole and of that large division of them included under the Crustacea, it is
probably true that a great deal of this knowledge is of a very fragmentary and unsatisfactory
nature. There is great need for detailed and full accounts of the development and organogeny
of many forms in order that the relations of the various members of the Arthropod type may be
clearly established.

The present work may be regarded as a contribution toward supplying the need just men-
tioned, but how imperfectly it is unnecessary to say.

' The plan of making observations upon other Crustacea for comparison with the more detailed
studies of Alpheus has been as yet ouly partially carried out. The early stages of Stenopus hispidus,
Homarus Americanus, and Pontonia domestica have, however, been followed, and less completely
those of Hippa talpoides and Palemonetes vulgaris.

Spence Bate (3) states that the shortened development of Alpheus was first described in his
memoir, with drawings, communicated to the Royal Society in 1876, from a specimen procured in
the Mauritius. He named his specimen Homaralpheus, “from the impression that species producing
a Megalopa could not be placed in same genus as those producing a Zoéa.” He says: “The orig-
inal of my drawing is 2"™™ in length and was procured from a specimen 14"™ long, resembling the
figure that I have given of Alpheus minus, Say. An inspection of this drawing (3, Pl. oxxu, Fig. 1)
leaves some doubt as to whether there was not an error in referring this form to the genus. The
general shape is unlike that of Alpheus, the abdomen being three times as long as the carapace,
and there appear to be only three pairs of thoracic appendages behind the chelipeds.

Packard (46) in 1881 was the first to describe a shortened metamorphosis for Alpheus heterochelis.
In some brief notes published in the American Naturalist of that year, he states that both this and
the small green Alpheus (A. minus) occur in abundance at Key West, Florida,in the excurrent open-
ings of large sponges. This fact is interesting, and probably significant also, as will be later
shown. Packard describes the first larva of this Florida form as mueh further advanced toward
the adult state than is the first zoéa of the Beaufort species, according to the observations of
Brooks. In fact it more nearly agrees with the first larva of a Bahaman Alpheus soon to be described,
in which the metamorphosis is nearly lost. “The Nassau form of Alpheus heterochelis has, as I have
recently ascertained, a complete metamorphosis. The bearings of these facts will be discussed
further on.

The larval development of the Beaufort Alphei was studied by Brooks (7) and a short
abstract of his results was published in 1882. This is all, I believe, that has been previously done
on the embryology of these Crustacea. Several abstracts of the present work appeared in 1887~88
(20-22). P

METHODS OF WORK.

Several species of prawns, such as Stenopus and Pontonia, repeatedly laid eggs while kept in
aquaria, and doubfless I should have succeeded equally well with Alpheus, if sufficient pains had
been taken. As it was, only two or three individuals gratified me in this respect, but in each case
the ova failed to develop. The animals were therefore taken from the sea with eggs in the earliest
phases of development, and were kept under observation in an aquarium for the length of time
required. The ova were then carefully removed from the pleopods, and were hardened at intervals of
thirty minutes or one hour or a longer time, according to the phase orage of theembryo. By obtain-
ing a number of series in this way the whole life history within the egg could be followed, and by

372 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES,

this means I was able to observe the peculiar movements of the wandering cells and the formation of
germ-layers, which are often very difficult to interpret, when werely upon material taken by chance.
Experience with the use of Perenyi’s fluid in preparing the eggs led me to discard this reagent
altogether, and to substitute for it Kleinenberg’s picro-sulphuric acid, made up either with water
or 30 per cent alcohol. The alcoholic solution works equally well and economizes time. The Pe-
renyi is too violent and uneven in its action. While it serves fairly well in some cases, it generally
swells out the membranes or shell by the rapid endosmosis, and distorts some part of the egg or
embryo in consequence. The egg is frequently deformed and the shell ruptured. ‘The ova should
be transferred directly from the killing fluid to 70 per cent alcohol, and they will then generally
retain their normal shape, and can thence be removed to alcohol of a higher grade for permanent
keeping. If, however, they are carried from the Kleinenberg fluid to a weaker alcohol (30 per
cent), distortion is sure to follow, the capsule bursting and the egg sometimes exploding.
Preparations of the entire embryo as well as sections were made, but very little was attempted
with the living egg. For surface preparations the hardened ova were first punctured to allow
the fluid to penetrate the shell more easily and they were then stained entire, in Kleinenberg’s
hiemotoxylon. They were afterwards shelled, when this was possible; saturated with paraflin by
the turpentine-parafiin method, and were then mounted. While the paraffin was congealing they
were carefully placed in position with a hand lens. This last important and often troublesome
process was rendered easy by the differential property of the stain, which affects only the embry-
onic cells, leaving the ylok, which in preserved eggs is of a light straw color, unaltered. The
embryonic tissues are thus made to appear nearly black on a light background. The embryo was
then cut away from the rest of the egg by the microtome razor; attached to the slide by collodion
and mounted in balsam; or the egg was cut in two and both halves were similarly treated. All
drawings which represent surface views excepting Fig. 10 were made from objects thus prepared.
In general, Kleinenberg’s heemotoxylon proved to be the best staining fluid, and it is especially
useful in this case, where the massive yolk contains numerous elements, the relations of which it is
important to determine. The carmines are less serviceable, since the food yolk is also affected by
them. Soda carmines (Beccari’s formula) proves to be incapable of removing pigment from the
eyes, although it is specially recommended for this purpose. This may be easily effected by soak-
ing the entire tissues in very weak solutions of nitric acid for a considerable length of time. Gaule’s
quadruple stain of hzeemotoxylon, eosin, saffranin, and nigrosin was also tried with excellent results,
but this method is very laborious, and since our inquiries do not extend in most cases, to cell
structure it is unneccessary.*
Perenyi’s fluid is sometimes available for swelling the chorion and thus aiding in its removal,
although the embryo is liable to injury. It is also helpful in studying the egg with low powers.
The food yolk, which is often dark green, is affected less actively by this reagent than the embry-

onic tissue. ‘The latter is turned to a waxy whiteness and is thus clearly defined for a short time,

but the yolk is soon decolorized unless the eggs are transferred to water, becoming pink, and finally
light yellow after preservation in aicohol.

PART FIRST.
y I.—THE HABITS AND COLOR VARIATION OF ALPHEUS.

Some facts of general interest have been gathered from a study of the Alpheus in its natural
environment on the coral shores and reefs of the Bahamas, and in giving these we will limit our-
selves mainly to the three species which have contributed the material for the history of the em-
bryo, viz: Alpheus minus Say, from Beaufort, N. C., A. heterochelis Say, from Beaufort, N. C.,
and Nassau, New Providence, and A. saulcyi, from Nassau, New Providence. The genus
Alpheus comprises numerous species spread over a large part of the globe, many of which are
closely connected by intermediate forms. From North America upwards of twenty species of
Alpheus have been described; five are known to inhabit the eastern coast of the United States,
three from Florida, and two others (A. minus and A. heterochelis), which range from Panama to as

“In studying the development of the lobster, which has also a large egg, I have found it necessary to adopt new
methods, especiaily in the treatment of the eggs for surface preparations. In most cases the egg-membranes are best
removed by the aid of hot water.

ro ‘
ee) ee ee

ean

>.

™

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 373

far north as Virginia. From Florida and Cuba nine species are recorded. I have found twelve
species of this prolific genus, or about one-half the number described for the whole American con-
tinent, inhabiting the beautifal little reef of growing coral called Dix Point to’the eastward of
Nassau Harbor and along the margins of the little bay which was just in front of our laboratory.
Another species (A. eebsteri Kingsley), first reported from Florida, was also discovered on Green
Key reef, a few miles from Nassau.

From collections which [ made at Abaco and Andros Islands, I am led to believe that the
different species are quite generally distributed in the Bahamas, and as these islands have prob-
ably been largely populated from the South, we may expect the same forms to occur at Cuba and
at other West Indian Islands, This genus, however widely distributed, is essentially tropical and
abounds in all coral seas. Of the great family of the Crustacea which make their home on the
submerged reefs of growing coral, Alpheus is perhaps the most prominent and thoroughly charac-
teristic. They pop out of almost every rock which is brought up from the bottom, and every loose
head or block of growing coral, with its clusters of alga, sponge, and sea fans, which you pull
from the reef, resounds with the click of their little hammers. ‘

Some of these animals lead a semi-parasitic life in sponges, or seclude themselves in the porous
limestone which forms the solid floor of the beach, and others, again, live under loose shells and
stones in the white coral sand. Some are highly and beautifully colored, and with few exceptions
the pigment is characteristic of the species for any locality. In all cases the claws of the first
pair of walking legs are enormously enlarged and serve as formidable weapons of defense so re-
markable in this genus, and in most there is the greatest disparity in the size of these claws, one,
either the right or left, being the larger. One species, the habits of which are peculiar, carries
the larger of these claws so folded under the body as to be completely concealed. It ean, however,
quickly withdraw this weapon and make a rapid thrust when an enemy comes near.* By the scis-
sor-like blades of the large claws a sharp metallic report is produced. This is true of nearly all the
species, and so abundant are many in these islands that a constant fusilade is kept up along some
of the shores at low tide. This snapping propensity is shared by both sexes whether in or out of
the water, and it is undoubtedly correlated with their pugnacions habits. If two males or females
of the same or different species are placed in the same aquarium, they will dismember each other
in a very short time, and one is usually literally torn to pieces. ;

The sounds emitted by Alpheus heterochelis are the loudest I have beard from any member of
this genus. We frequently kept this species in glass dishes in our room for several days at a time,
and sharp reports liké the explosion of a small torpedo or pop gun were heard at intervals through
the day and night. It sometimes swims with its large claw so widely opened as to suggest dislo-
cation. This weapon then reminds one of a cocked pistol, and the report apparently follows in
the same way\that the click follows the impact of the hammer on the lock. I have given this
mattter no closer attention, but find that, Mr. Wood-Mason, who is quoted in a notice on“ Stridulating
Crustacea” t in “Nature,” (65) has offered another explanation. According to this observer the
sound always accompanies a sudden opening of the claws to their fullest extent, and may be caused
either by impact of the dactyle upon the joint to which it is articulated or “by foreible withdrawal
of the huge stopper-like tooth of the dactylopodite from its pit in the immovable arm in the claw.”
It seems most probable to me that the sound is caused by impact, and most likely by the rapid
closure of the finger into its socket.t :

“This species is entirely new. The large concealed claw suggests a poison apparatus. The “ fingers” are ex-
ceedingly slender and sharp at the points. Although kept for over a week in an aquarinm it emitted no sounds.

t According to Wood-Mason sound-producing organs in Crustacea were first brought to notice by Hilgendorf, in
V. der Decker’s “Reisen in Ost-Africa (Crustaceen),” and were afterwards observed by himself in his dredging ex-
pedition to the Andaman Islands. The stridulating organs—scrapers and rasps—may be either on the carapace and
appendages or on the appendages alone.

{Both Kent and Wood-Mason speak of the sounds emitted by the Alphei as if produced by the extension or
opening of the claw. As pointed out above, it is just the other way, the sound following upon the impact of dactyle
and propodus, when the tooth of the dactyle is not pulled out of its socket but driven into it. None of the conditions
of piston moyement are present. The walls and floor of the pit are relatively soft, while the tips of the claw are
dense and stony. The ‘‘click” can be artificially produced when the claws are clamped with rubber, whether the
‘*stopper” is present or not.

374 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

In Alpheus heterochelis the dactyle of the large pincers is a curved blade which shuts down

into a groove on the occludent margin of the “thumb,” and closes over the latter like a pair of
shears. The huge stopper-like tooth is borne on the inner and proximal edge of the dactylopodite
and fits neatly into a corresponding pit in the “thumb,” in line with the groove just mentioned.
The object of this plug is evidently to steady the movable dactyle and to prevent lateral strain
and the dislocation which might result, and thus to give it a strong grip on any object which it
has seized. In alcoholic specimens in which the relations of the parts are well preserved the stop-
per works freely in and out the well, and not like a “tightly packed piston from a cylinder closed
at one end.”

(The claw is widely opened, before the sound is produced, but the sound is not produced while
the claw is open, but at the instant when it is violently and suddenly closed. It is due to the
impact of the “thumb” and “finger,” and I have frequently seen specimens of A. heterochelis,
when prepared for combat, facing each other for several seconds with claws distended to the
utmost. In these cases the “snap” does not come until the claw is closed. In fighting the 7
claw is not used as a clasper, but as a saber. The sharp external edgeis a weapon of such efficiency
that I have seen individuals killed and almost cut in two by a single blow.—W. K. B.)

A large brown sponge, Hireinia arcuta, which is not to be mistaken, grows on the shallow
reefs and off the shores of all the Bahama Islands which I visited. It is found from just below
low tide mark out to one-half a fathom or more of water, where its great size and sooty brown color
distinguish it at once on the white bottom. These “loggerheads” are round and much flattened (the
smaller ones more vase-shaped), and of a coriaceous texture; they sometimes measure 14 feet in
diameter. There is commonly one, sometimes two, large exhalent chimneys into which small fish,
young spring lobsters, and other Crustacea, often beat a hasty retreat. It is easily broken open since
it has no consistent skeleton. Ifa sponge colony of this kind is pulled and torn apart, one is certain
to find it swarming and crackling with a small species of Alpheus, which quarter themselves in
the intricately winding pores of the sponge. The sounds emitted from every fragment of these
mutilated sponges remind one forcibly of ‘‘ those made when sparks are taken by the nuckles from
the prime conductor of a small electrical machine,” as Wood-Mason remarks. Hundreds of indi-
viduals may be collected from a single large specimen.

These animals have an average length of about 12™", They are nearly colorless, excepting
the large chelie, which are tipped with brown, reddish orange, or bright blue. The females are so
swollen with their eggs or burdened with the weight of those attached to the abdomen that they
can crawl only with great difficulty, if taken from the water. The eggs are few in number and of
unusually large size, their diameter varying from one-twenty-second inch to one-twenty-fifth inch,
and their number from six to twenty. These are most commonly yellow, but may be either bright
green, olive, greenish white, brown, brownish yellow, or dull white. The ova and ovarian eggs
have always the same tint in the same individual. Although translucent and apparently colorless,
upon close inspection the body is seen to be sprinkled with cells of reddish and yellow pigment.

Another quite different sponge grows on all the reefs in from one to two fathoms or more of
water. There are several varieties of this, which may be told by their olive green color, yellow
flesh, and clumpy, irregular shape, as well as by the putrescent mucous which some of them pour
out when broken open. In about nine ont of ten of these sponges one will find a single pair of
Alpheus (rarely more than this), which resemble those living in the brown sponge, but differ from
them in several important points. We are concerned at the present with the color variations only.
They are distinguished by their large size (averaging about 23" in length) and uniform color.
The females exceed the males greatly in bulk, owing to the large size and number of their eggs.
Tn both sexes the large claws are bright red (v. Pl. rv, and for details section Tv).

The female is practically inert during the breeding season, and at such times is well protected
in her sponge or against any green surface by the bright green ovaries which fill the whole upper
part of the body and by the mass of similarly colored eggs attached to the abdomen below. Only
two pairs, or four individuals, out of a hundred or more which were examined showed any variation
from these colors. In these the eggs were yellow, and the pigment on the claws was more orange
than red. The table which follows shows the variations between two large females taken, respec-
tively, from the brown and green sponges, and between the size, number, and color of the eggs.

MEMOIRS OF THE NATIONAL, ACADEMY OF SC] ENCES. 375
Habitat of Alpheus. | Length of 9. aye of Diameter. Color. Color of adult.
Inches. Inches.
Brown sponge. .- + 19 ay Yellow (variable)... .| Large chelw,red (blue
or brown in others. )
Green sponge. --- 1}; 347 vs Usually green; in | Large chelw, orange-
this case yellow. red.

These two forms, although apparently distinct, are seen, however, by closer study to belong to
the same species; but besides the more superficial variations just mentioned, there are others of a
more remarkable character, the morphological significance of which is considered in sections IV
and v.

Of this species, Alpheus saulcyi, Guérin, it is necessary, for descriptive purposes, to distin-
guish two varieties, viz:

Alpheus saulcyi, variety longicarpus (from brown sponges),
Alpheus sauleyi, variety brevicarpus (from green sponges).

These two varieties shade completely into each other by numerous intermediate forms. The
longicarpus varies greatly in size and in the color of the body and eggs (besides the other more
profound variations mentioned in section V), while the brevicarpus type from the green sponges is
more uniform in size and stable in color and other characters. The former variety is well pro-
tected from outside enemies while in the tortuous mazes of its sponge, as its great numbers would
show, if any evidence under this head were needed. The enemies which invade them successfully
seem to be parasites.* y

Possibly the variety inhabiting the green sponge does require color-protection, especially since
the females are very inert during the breeding season. They are, indeed, admirably protected
when exposed on the green surface of sponges, alge, ete. The bright color on the tips of the large
claws, which only are protruded from the places of concealment, recall the similarly colored heads
of boring annelids, which abound on the reef, but this fact may have no significance.

It seems quite probable that if we have in this Alpheus a case of protective coloring, it is due
very largely to individual adaptibility. This view implies great individual plasticity, which does
not appear in any of the species of Alpheus known to me within a restricted area.

The colors of certain Crustacea, and also the colors of their eggs, are kuown to vary greatly
with the surroundings. In the Alpheus, parasitic in the brown sponges, these colors vary consid-
erably where the surrounding conditions are the same. However, the color of the ovarian eggs is
always the same as that of those already laid, and, although these animals were kept for several
days at a time in differently colored dishes, I never observed any very marked change in the color
of the ovary, but these experiments were not continued long enough or carefully enough to be con-
clusive. The eggs of Alpheus heterochelis are almost invariably of a dull olive color, while, as in
the case of the parasite of the green sponge, about one in a hundred has bright yellow eggs. In
the first case at least this may possibly be an instance of reversion to one of the original colors
from which the green was selected. In most species of Alpheus the color of the eggs is fixed and
uniform for any locality, and, as already suggested, may have a protective significance; but in a
few other cases, where this is not true, the color is not only variable in different individuals, but
probably also in the same individual. ;

Alpheus heterochelis from Beaufort, N. C., is uniformly of a dark olive-green color, with some
red and blue on the appendages. It lives in the beds of oyster shells, which are more or less

*A parasitic Isopod, probably a Bopyrus, is found on both the varieties, but is most common with the dweller in
the brown sponge.» It appears as a tumid bunch, firmly rooted in the branchial cavity or to the under side of the
abdomen. In this connection I will mention another curious parasite which was found infesting the eggs of a single
female taken from a brown sponge at Abaco. This is a large, spherical, unicellular organism in the encysted state.
The egg, with the embryo, is packed full of them. (v. Fig. 199 and section 1v, Part Second.)

In looking over a collection of unpublished drawings of Crustacea, made by the associates of Louis Agassiz and
deposited in the library of the Museum of Comparative Zoélogy of Harvard College, I find a sketeh (by H. J. Clark,
December 23, 1857) of a Bopyrus taken from the branchial cavity of Alpheus heterochelis.

376 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

exposed at low tide. Alpheus minus has a similar environment and is similarly colored. Alpheus
heterochelis from Nassau, New Providence, on the other hand, lives under loose stones, amid the
white coral sands of the beach, and is noticeably transparent, looking as if the color had been
bleached out of it. The body is sprinkled with dots of brown pigment. The claws and legs are
pale greenish. Young and old are invariably colored alike. “ :

In a collection of adult Alpheus of either sex of the same or of several species, where there is
a difference in size of the large claws, it is noticed that either the right or the left, indifferently,
may be the greater. As we will see, this differentiation of the chele begins in one instance before
the animal is hatched. Is this right and left handed condition to be explained by inheritance
from the parents? In about forty larvee of a small brood of Alpheus saulcyi, all invariably had the
left claw enlarged, and in a smaller number (al! that were preserved), from another female of the
same species, the left chela was also in each case the larger. This would indicate that the young
of the same mother have always the same claw, either right or left, the greater, and that this phe-
nomenon is one of direct heredity from the parents. But to prove this it is only necessary to trace
right and left handed broods to parents which are themselves right and left handed, respectively.
This, unfortunately, I have not done, as my attention was not called to the subject while at the
seashore.*

The breediug season of Alpheus begins at Beaufort, N. C., about April 1. It covered the
period of our stay at Nassau (March to July), and probably began earlier and lasted considerably
later.| There the temperature is high and remarkably constant, the annual range being about 15°
(temperature of air 70° F. in March, 80° in June), and in consequence the early phases of devel-
opment are rapidly passed. Not one prawn in a hundred was found with eggs in an earlier stage
than that of yolk segmentation.

II.— VARIATIONS IN ALPHEUS HETEROCHELIS.

A renewed comparison of Alpheus heterochelis with the Nassau form lends support to the con-
clusion already reached that we here have to do with two varieties of the same species. There are
certain differences, which systematic zodlogists might regard as of specific value, but they are no
greater than we have proved to exist among individuals of the same species living in the same
sponge. (v. Section V.)

The Nassau specimens average smaller, but the chief difference lies in the shape of the small
chela. The propodus of this appendage in the Nassau form is relatively shorter and tbicker in
both sexes. Both fingers are nearly cylindrical, and covered with hairs, which are distributed
either singly or in tufts. In the Beaufort heterochelis there is a striking variation in the small
chela which appears to have escaped detection. Judging from the small collection at my command
it is a sexual variation. In the females the small chela is like that of the Nassau form, but is
usually longer and slenderer. The dactyle is about one-half the length of the propodus. In
the males the dactyle is relatively much shorter, and has a median longitudinal carina which is
continued into the apex of the claw. In transverse section the dactyle is trihedral, with two con-
cave sides, corresponding to the deep groove on either side of the keel. These grooves are fringed
with a row of stout plumose set. Similar rows of setz occur on the sides of the opposing
“ thumb.”

Perhaps the most interesting variation which I have observed in the Beaufort heterochelis has
reference to the size of the egg. The eggs in this locality have an average diameter of about one

“Mr. J. J. Northrop, of Colambia College, while at Nassau in the winter and spring of 1890, kindly offered to
collect for me some specimens of Alpheus saulcyi with young. On February 10 he collected six females, five from green
sponges, one of which had a brood of sixteen young, and one small female with three larve from the ‘‘ loggerhead”
sponge. In the first instance the left chela was the largest in the mother and in each of the sixteen young. Yn the
latter, two had the right claw enlarged and one the left. The inference is suggested that when the claw of the same
side is invariably the greater in all the young, this character is doubly inherited from both father and mother, but the
data are insufficient to settle this point.

t Professor H. V. Wilson found this species breeding around Green Turtle Key from July until December. Mr.
Northrop found newly hatched young early in February. It therefore breeds the year-through, which is probably
true of many of the Crustacea.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 377

twenty-fourth inch, but two females were found which carried a few bunches of very small eggs, nor-
mally glued to the anterior swimmerets. These eggs measured only one fifty-third to one sixty-fifth
inch in diameter, that is, the contents of the smaller was about one-twelfth that of the larger egg.

This occasional production of very small eggs exhibits a tendency, which is still present in
the species of this locality to-day, to revert to its old metamorphosis long since laid aside.

lll.—THE ABBREVIATED DEVELOPMENT OF ALPHEUS AND ITS RELATION TO THE ENVIRONMENT.

Related species, as a rule, resemble each other more in their early stages of development than
in their adult state. This is not, however, invariably true, since all animals, whether young or
adult, must adapt themselves to their environment or be destroyed. It is probable that animals
in all stages of growth are equally plastic and tend to vary with the varying conditions of life.

The early life in large classes of the animal kingdom, as fishes, birds, and mammals, is spent
either in the protecting membranes of the egg or within the body of the parent, and is thus but
slightly affected by external conditions, and suffers little change in consequence. In other groups,
on the contrary, and in the Crustacea in particular, the case is very different. Here the young
are usually hatched in a very immature condition, and lead a life of their own at the surface of
the ocean, wholly independent of their parents. They have accordingly adapted themselves to this
mode of life, and the variations thus entailed have led to the production of the zoéa, a locomotor
larva, fundamentally different from the aduit. We may regard the zoéa as a secondary, adaptive
form, directly descended from an ancestral protozoéan type. After passing a longer or shorter
period (usually of several weeks) at the surface of the sea, the adult state is gradually reached
through a complicated series of changes, and the animal adapts itself to new conditions on the sea
bottom or on the shore.

Now, if the habits of the adult and larva should tend to converge, if the adults should adapt
themselves to an entirely new environment, which it is necessary for the young to become fitted
for at once as soon as hatched, we would expect that the zoéal stages, formally assumed to bridge
over a gap which no longer exists, would be dropped or shifted to the egg. This seems to have
actually taken place, and is illustrated in a remarkable manner in the genus Alpheus.

Most of the species, which are very numerous, inhabit the shores, in common with many
related forms, and, as already stated, they abound on coral reefs. They all, as a rule, hatch as
zoéa-like and have a complicated metamorphosis. Two species have been discovered, however,
which have adopted a parasitic life, and in each the larval period is accelerated. In one, which is
semiparasitic, the metamorphosis is partially abbreviated ; in the other, which is completely para-
sitic, the metamorphosis is completely lost. Still more interesting and significant is the fact that
one of the species in one locality is nonparasitie and has a complicated metamorphosis, while the same
species from another locality is parasitic and has the metamorphosis abridged.

We will now consider more particularly the history of these two forms, in order to make a
clearer comparison. The species are—

Alpheus heterochelis, from Beaufort, North Caralina.
Alpheus heterochelis, from Key West, Florida.
(2) Alpheus saulcyi, from Nassau, New Providence.

Alpheus heterochelis, from Nassau, New Providence.
ws

ALPHEUS HETEROCHELIS FROM THE BAHAMAS.

This species, found at Nassau, exemplifies the development common to the genus, as seen, for
instance, in A. normani (Kingsley), which is closely associated with it, A. minus Say, and in many
other Bahaman forms. It is one of the common species at Dix Point, and may be found in abun-
dance on the shore of the little bay, in pools left by the ebb tide, under shells or loose fragments
of coral.

First larva (length = } inch).—The three pairs of maxillipeds, each with long exopodites ending
in feathered hairs, are the principal locomotor organs. Two pairs of rudimentary thoracic legs
are present, All the abdominal segments, but none of their appendages, are formed.

378 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.
The antennules consist of a stout jointed stalk, the terminal segment of which bears four 3

sensory filaments. A long plumose spine springs from the extremity of the second joint on the
inner side.

The antenne are biramous, the two branches arising apparently out of a common basal segment.
The outer division is a seale-like plate. It bears on its extreme inner border a row of plumose hairs,
eight to ten in number. The endopodite is slender and shorter than the scale. It terminates ina -
short spine or denticle, from near the base of which springs a long plumose hair. The eyes are
large and uncovered. The mandible is simple.

The telson is a broad triangular plate, the terminal side of which is garnished with the charac-
teristic zoéal spines, the number, relative size, and position of which vary slightly in the different
species. There are in this case eight pairs of these spines. The first or median pair is rudimen- i
tary; the second is not half the length of the third. The lateral angles of the plate are each
prolonged into a short lobe, bearing three spines. There is no marked median notch, but there is
a slight median depression. The rudiments of the sixth pair of abdominal appendages are plainly
seen.

Second larva.—With the first molt the endopodites of the maxillipeds lengthen. Three pairs
of rudimentary pereiopods are now present, the last of which are the longest. Of the pleopods
only the sixth pair are represented, whether free or not was not observed.

ALPHEUS HETEROCHELIS FROM BEAUFORT.

The peculiar metamorphosis of the Beaufort Heterochelis was described in 1884 by Brooks, who
also showed that in this respect it departs widely from the associated Alpheus minus.

The form in question is hatched as a larva with preparations for the schizopod stage. It has the
usual swimming organs, but all the thoracic legs are present in the condition of rudimentary buds.
The abdominal segments are formed, and the buds of the first five paiis of feet belonging to them.
The eyes are not completely covered by the carapace. At the first molt the rudiments of the
sixth pair of abdominal feet are added, and the larva undergoes profound changes. All the ap-
pendages are now functional and the eyes are nearly hooded. With later molts the adult char-
acters become more pronounced, but the marked difference of the great claws appears only after
several months.

ALPHEUS HETEROCHELIS FROM FLORIDA.

The short description, given by Packard in 1881, of the first larval stage of this species from
Key West, where it inhabits sponges, has already been alluded to. From this we infer that the
development is considerably more abridged than in the Beaufort case. This is also indicated by his
figure of one of the abdominal appendages. He says: The eyes are nearly sessile, the yolk nearly
absorbed, although the embryo (in the egg) was near the time of hatching. Theantennz are “ well
developed.” All the thoracic legs are present, their joints distinct, “ the first pair about twice
as thick as the others, the claws rather large, but not so disproportionately so as in the adult form,
but as much so as in the larva in the second stage of the lobster. Abdomen broad and flat. spatu-
late at the end, much as in theadult. There were five pairs of abdominal feet or swimmerets, each
with endopodite and exopodite, like those of the second larval stage of the lubster.”

ALPHEUS SAULCYI FROM THE BAHAMAS.

In this form, the metamorphosis of which is fully described in another paper, we have either
an abridged development in which the general adult characters, very marked in the first larva,
are all acquired in twenty-four hours after hatching, or a case where the short metamorphosis is
done away with entirely, so that the animal leaves the egg in the full adult form.

Comparing the histories just given with the one before us, we find that the first larva of
Alpheus saulcyi is about equivalent to the third larva of the Heterochelis from Beaufort, and rather
more advanced than the first larva of this species from Florida.

The eggs of the Alplei, with the development unabridged, are invariably small and quite
numerous. In the two species, however, with shortened metamorphosis, the ova are fewer and many
times larger. Moreover, as would be expected, the degree of abbreviation is correlated with the

—
ae

Re ete se

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 379

size and number of the eggs. These and the other facts which we have been considering are
given in tabular view below:

Species. Habits. Metamorphosis. eee eee Lae 4 f
)
| Inch. Inches.
Alpheus minus (from Beaufort).| Non-parasitic - ...--- Complete ...-.-.. -- "500 ae | 4-1
A. heterochelis (from Nassau) ...|....do0 ...-....-..----|---- 0 BE eS 300-500 toads | 8_]}
A. heterochelis (from Beaufort) .|....do ......-. .-| Abridged. -----| 150-300 ty- or 1-1}
A. heterochelis (from Florida) .-| Semi-parasitic....--.}....d0 -...--...---.|.--------- {ne ed PEAR coe
A. sauleyi (var. breyircarpus) ...| Completely parasitic.| Nearly lost ...-.- -. 100-350 vr | 4-1}
A. sauleyi (var. longicarpus)....|....do .........---.--| Completely absent 5-20 v5—vy | i ll
(in some cases). /

* Number not accurately determined.

The eggs of Alpheus are usually spherical when freshly laid, but they change their shape,
becoming more elongate in course of development and increase somewhat in size.* The eggs of
A, saulcyi are usually oblong. They vary from one twenty-eighth to one twenty-third of an inch,
taking the mean of the long and short diameters. The extreme limits of the number of eggs vary
somewhat from the numbers given above, which are the average limits.

In the genus Aipheus we thus have several stages in the abbreviation of the metamorphosis
between the macronran zoéa stage and the adult form. What is the cause of this gradual suppres-
sion of the zoéa like form? The conclusion seems to be unavoidable that in the Bahaman species
this shortened life of the larva is directly related to the conditions of life. As the adults of the
species in question became more and more dependent upon a semiparasitict mode of life, it would
be clearly beneficial to reduce the larval period, in order that the young might be hatched fitted to
live in an environment similar to that of the adults. It the zoéa brood were swept ont to sea by the
tides, and were to spend several weeks in the larval condition at the surface of the ocean, the
chances for large numbers to find particular sponges along the shores, when the adult state was
reached, would be greatly lessened. It is likely that the larvie of this Alpheus are never carried far
from the shores, but while they undoubtedly leave the sponge in which they are born, they prob-
ably establish themselves very soon in a newone. (The young remain a short time after hatching,
attached to the swimmerets of the mother.)

This supposition is strengthened by what we know of the peculiar history of Alpheus heterochelis.
The Nassau heterochelis probably never changed its adult habits or adopted a parasitic mode of life ;
consequently it has retained undisturbed its complex larval development. The Floridian form has
become a parasite, and its metamorphosis is accelerated as the result. From this the Beaufort
Alpheus with its less abridged development has doubtless been derived (the species extending north-
ward from the Gulf of Mexico), and it is within the possible, at least, to suppose that in this form
the metamorphosis, once lost by parasitism, is now being reéstablished.

No fewer than three species of macroura, together with the Alpheus above described, occur in
the large brown sponges (/Hireinia arcula) of the Bahama islands. These (one of which is also an
Alpheus) live in the larger oscula, are less regular in their oecurrence, and evidently have not
adopted a stationary parasitic life. In none of them is the metamorphosis of the larva abbreviated.
Alpheus minus is also reported as occurring in the large exhalent openings of sponges at Key West,
but in this case we do not know, first, whether this is a fixed or only a transient habit, and
secondly, we know nothing of its metamorphosis under these conditions.

Thus while in Alpheus the abbreviated metamorphosis may be explained as an adaptation
to a parasitic mode of life, the question is probably often complicated by conditions which are not
easy to determine. There is a general tendency among the higher forms of certain groups, as in
the Cephalopods among the Mollusca, to reach the adult conditions rapidly by omitting some of
the early embryonic stages.

* An egg of A. sauleyi var. longicarpus, just ready to hatch (Pl. xxt, Fig. 5), measures ;45 by fy inch.
t The Alphei which inhabit sponges are commensals rather than parasites in the strict sense. They derive pro-
tection from the sponge colony, and receive the benefit of the circulating currents of water which are set up within it,

880 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

An abridged larval development has been attributed to the following macroura: The lobster
Homarus americanus; the crayfishes, Hippolyte polaris; Paleemonetes varians; Palemon potiuna; Pa-
lemon adspersus and Briphia spinifrons (as first observed by Rathke, according to Packard); Bytho-
caris leucopsis (observed by G. O. Sars, according to 8S. I. Smith); Alpheus heterochelis, and A. sauleyi.
To this list we must probably add the names of many deep-sea decapoda, Munidopsis, Glypho-
crangon, Elasmonotus inermis, Sabinea princeps, Acanthephyra gracilis, and Pasiphaé princeps, as
inferred by S. I. Smith, on account of the extraordinarily large size of their eggs. An egg of
remarkable dimensions is that of ‘ the little shrimp (Parapasiphaé sulcatifrons,) which carries only
fifteen to twenty eggs, each of which is more than 4 millimeters in diameter, and approximately
equal to a hundredth of the bulk of the animal producing it—a case in whieh the egg is relatively
nearly as large as in many birds!” ‘Although the great size of the eggs,” says Prof. Smith, “is
highly characteristic of many deep-water species, it is by no means characteristic of all, and the
size of the eggs has no definite relation to the bathymetrical habitat, and is often very different in
closely allied species, even where both are inhabitants of deep water (59).”

The larval life of both terrestrial and fresh-water Crustacea is generally short as compared
with that of marine forms, and the case of the crayfish may find an explanation in the well-known
law that fresh-water life tends to shorten the development, as is Shown in a remarkable manner in
the fresh-water variety of Paleemonetes varians, described by Boas (4). Why, on the other hand,
it is beneficial for the lobster to abbreviate its larval development is not plain, since its young at
the present time hatch apparently under the same conditions as other pelagic larvie, and, like
them, swim at the surface of the ocean. S. I. Smith (58) and Ryder (55) have given accounts of
the larval history of the lobster. (Since this paper was written I have undertaken a revision of
this subject, and the results will be given in a fully illustrated report to the United States Com-
missioner of Fish and Fisheries.) While this animal hatches in a precocious state its life at the sur-
face is by no means short, since, according to Ryder, it ordinarily requires seven weeks to pass
through.six molts. The first larva hatches in a schizopod stage, but there are no abdominal legs
and theantenne are somewhatrudimentary. The first ecdysis, according to Ryder, does not occur
until from three to six days after hatching.* It is in the second stage that the second to fifth
pairs of abdominal appendages make their appearance.

The third stage is preceded by a molt ten to fifteen days after hatching, and now the append-
ages of the last abdominal segment are formed. After the fourth molt (fifth stage) the young
lobster, now 14™™ long, quite closely resembles the adult. It swims more on the bottom. The
flagella of the antennz are equal to the cephalo-thorax in length. The exopodites of the thoracic
legs are reduced to bare rudiments. The chelipeds show adult characters. The first pair of swimn-
merets are developed in the seventh stage, at the end of which ee is a decided difference between
the great claws.

It will be seen that the fifth-stage in Ryder’s account, attained at the end of the third week,
nearly corresponds with the third larva of Alpheus sauleyi (Fig. 8, Pl. XX1) as it appears twenty-four
hours after hatching, but the latter has the more decided adult characters. The young Alpheus
is further advanced than the lobster at the time of hatching and reaches maturity in a remark-
ably shorter period.

Boas calls attention to the fact that while the young of the salt and fresh water forms of
Palemonetes varians are very different, the adults of these two varieties resemble each other very
closely. Much more remarkable is the case of Alpheus heterochelis, even if we regard the Nassau
form as a distinct species, and that of Alpheus sauleyi, where we have the same species living in
the same sponge, hatching now as a larva and now as a form possessed of all the external adult
characters.

Both the long and short metamorphosis has been attributed to the West Indian shore crab
Gegarcinus. This highly colored crab (Gegarcinus ruricola) is very abundant at Nassau, and from
its exceptionally large egg we may safely infer that the development has here been shortened.
Fritz Miiller (42) has found abbreviated development in the South American crabs, Trichodactylus
and dAglea (‘mountain crab”). . :

“A delicate moulted skin, which is easily overlooked, either comes off with the egg membranes at the time of
hatching or is shed shortly after, as my own observations have clearly shown.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 381

The habits of the hermit crabs, though secondarily acquired in comparatively recent times,
have had no tendency to shorten the larval period. This is also true of the Pinnotheres. Simi-
larly the commensalism of such forms as Pontonia domestica, which lives in the mantle cavity of
several species of Pinna, has in no way affected its er atopiant

IV.—THE ADULT.

The Alpheus whose development has just been traced was provisionally named Alpheus pre-
cox (22), in allusion to its greatly accelerated metamorphosis. It has since been found to agree in
most particulars with the description and figure of Alpheus saulcyi given by Guérin in Ramon de
la Sagra’s History of Cuba (18). In Guérin’s drawings the long spine (squamal spine) of the
antenne is represented as continuous throughout its length with the scale, and the carpus of the
second pair of thoracic legs as divided into three segments. The segmentation of the carpus of this
appendage is one of the most constant of specific characters. If these figures are accurately
drawn, the two forms in question are certainly not specifically identical; but though not at first able
to satisfy myself on this point, or to decide from the short and imperfect description, it seemed
best after further study to adopt Guérin’s name.

The systematic zodlogy of the genus’ Alpheus is in a very unsatisfactory state, and in the
absence of adequate and well executed drawings, and too often with only vague or general descrip-
tions, the attempt to idengify the less known species is apt to be attended with most doubtful
success. :
It is now necessary to complete the account of the metamorphosis of this Alpheus by giving
a description of the adult form. The Alpheus sauleyi resideut in certain ty sponges found on
the Bahama reefs is regarded as the typical form of this species.

DIAGNOSIS.
‘

Carapace ends anteriorly in three spines. The median spine or rostrum inclined, especially in the
female ; arises from the edges of the carapace, like the lateral or orbital spines; barely surpasses the latter
in length; without keel. Body and appendages generally smooth; large chela slightly twisted, smooth, no
transverse constrictions; small chela subcylindrical, short; dactyle nearly straight, slender, one-half as long
as propodus; carpus of this appendage short. Aural spine of inner antenna variable in length; rarely sur-
passes the middle of the second segment. Basal segment of outer antenna is produced into an outer, inferior
spine, and an upper rudimentary spur; articulated with it is a squamal spine, on which is developed a con-
spicuous scale. Carpus of second pair of thoracic legs superficially segmented into five parts.

SPECIAL DESCRIPTION.

Length: Smallest found in green sponges, 9.5", 4; largest, 42™", 2; average length, 25 to
30™™, Females exceed the males a little in length, and greatly surpass the Jatter in size when
swollen with their eggs.

Color: The color of this form is shown in Pl. rv. Large claw vermillion above, fading out
towards proximal half, and nearly colorless below. On upper face of claw a transverse colorless
band is often seen. Small chela often tinged with red, also the terminal segment of the third pair
of maxillipeds. Body, pale, translucent, with scattered cells of reddish or yellow pigment, subject
to quantitative variation, and visible to the naked eye on close inspection or by aid of a lens.

A young male which was kept for several days in an aquarium molted and lost completely the
bright color of its claws. Sexes are colored alike, excepting the eggs and ovaries of the female,
which are bright green.

In one or two instances a pair of iead Crustacea were found which exhibited a variation from
these tints. In these cases the male and female were of light-reddish orange and the claws deep
orange red, darkest on the “ fingers” ; eggs and ovaries of female golden yellow. Length of 2,33".
Number of eggs attached to abdomen, 347, The male in this case also, after a moult, was apparently
colorless, contrary to the rule that upon molting the colors are enhanced.

. The carapace is smooth, translucent, and, like the abdomen, takes on more or less the hue of
the yellow or green ovaries. It ends anteriorly in a trident, formed by the median rostrum and

382 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

ocular spines. The rostrum is short, subacute, broader at base than long, feebly convex above,
without crest. The orbital spines are separated from the rostrum by a shallow superficial groove,
and the marginal notch on each side has a regular -shaped outline. Length of spines and width
of notch are slightly variable.

The lateral compression of carapax is not marked. Frontal angle (angle made by middle line
above and below rostrum, greater in 2 thanin ¢. In some females with the carapace bulged out
by the ovaries the angle is as great as 45°. In males without conspicuous “forehead” frontal
angle, 10°.

The telson ends bluntly. It is two-thirds as broad as long, and twice as broad at base as at
apex. ‘There is a single pair of short spines at the posterior extremity on either-side the middle
line, and two (or more) separate spines upon either side further forward. There is a wide and
shallow median depression.

The compound eyes are conspicuous, owing to their dark pigment and the transparency of the
carapace, and in the largest adults they show no traces of degeneracy. There is a permanent
ocellus (P]. xx, Fig. 18), which occupies the same position and has the same characters as at birth.
It consists of a pigmented body embedded in a short median papilla, situated below the compound
eyes and between the bases of the antennules. .

The antennules (Fig. 4, Pl. xx111) consist of a three-jointed stem or protopodite, an exopodite,
and endopodite. The first segment of the stem is largest and bears an external spine (aural spine),
which protects the auditory sac. The latter is large and conspicuous in this genus. It usually
contains some pigment cells and grains of sand. Second segment about half as long as first;
third, four-fifths as long as second. Endopodite one and one-half times the length of stalk, slender.
Exopodite compound, a slender flagellum branching from near the end of the stouter proximal
portion. On the under side of the latter the sensory filaments (olfactory sets) are borne, distrib-
uted in seven to ten bunches of two to three in a bunch.

The antenne (Fig. 8, Pl. Xx11) are composed of three parts—a basal portion (protopodite),
which carries a squamous spine (exopodite), and on its inner and lower side a léng three-jointed
stem, which bears a flagellum (endopodite).

The protopodite consists of a proximal segment (coxopodite) and a larger distal one (basipo-
dite). A prominent papilliform process is seen on the inner side of the coxopodite at its point of
junction with the basipodite. Upon it the duct of the green gland probably opens to the exterior.
The basipodite is continued into a prominent spine below and into one or more rudimentary spurs
above. To it is articulated a long, stout, scale-bearing spine. The scale plate, usually shorter
than the spine and attached to it for less than half its length, is fringed on its inner free edge with
plumose sete. The antennal stem or peduncle consists of two short proximal segments and along
distal one, which carries the multarticulate flagellum. The latter is often hairy, and is two to
three times the length of the peduncle. The relative lengths of the different parts for an average
specimen is shown in Fig. 8, Pl. xx11, and in Pl. tv.

The mandibles (Fig. 3, Pl. xx111) are strongly bifureate, as is characteristic of the genus. The
larger division is finely tuberculated, while the masticatory surface of the slenderer branch is
raised into sharp teeth. This bears a jointed palp (endopodite) on the inner side. The mandibular
palpus is short; its terminal segment large and hairy. _

The first maxilla (Pl. xxiv, Fig. 7) consists of three divisions—a smaller branch (endopodite),
a larger branch (basipodite), divided at the apex and terminated by several long spines, and a
larger spatula-shaped fork, the maxillary surface of which is beset with spines (coxopodite). (v.
Description of figure.)

The second maxilla (P]. xxtv, Fig. 9) is composed of three portions. (1) The long respiratory
plate; the “bailer” or scaphognathite, fringed with a row of sete. (2) An outer and lobulated
division (coxopodite and basipodite), the inner edge of which are closely set with bristles, and (3)
a median rudimentary endopodite.

The first pair of maxillipeds (Fig. 7, Pl. xx111) are made up of a long, strap-shaped exopodite,
with jointed setz at the extremity and a small setigerous plate at its base; a small, two-jointed
endopodite, protopodite, and epipodite. The protopodite is divided by a fissure into two lobes, a
larger (basipodite), with dense rows of bristles on its maxillary surface, and a smaller division
(coxopodite). The epipodite is an oblong plate, united by a short stalk to the protopodite.

en eS Me, See

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 383

The second pair of maxillipeds (Fig. 6) has a long, strap-shaped exopodite, like that of the
first pair. The endopodite is incurved, and segmented into at least four parts. The dactylopo-
dite or terminal segment is the longest, and is thickly studded with serrate bristles and setie.
There is a small oval epipodite.

The third pair of maxillipeds (ig. 5) consist of a basal piece (coxopodite) and a long two-
branched appendage. The large branch consists of three distinet segments—a long proximal one
(basipodite (?) and ischiopodite), a shorter one (meropodite), and a long terminal segment (carpo-
podite, propodite, and dactylopodite). The exopodite springs from the base of the first segment,
and is about equal to it in length. The lower surface of the two terminal joints is covered by
numerous transverse rows of serrated bristles, and the end of this appendage is armed with several
spines. , .

The first pair of pereiopods or walking legs bear the great chelw (‘“hands” or “‘shears”).
‘he chelz are very unequal. Large claw (relatively larger in ¢) smooth, slightly twisted; outer
and upper border sometimes marked by a linear crest; several spurs or tuberosities near the
articular surface of the dactyle; dactyle shaped like end of pruning knife, its concave inner
margin and tooth-like point shutting into a groove of the opposing “thumb.” This groove of the
propodus is continuous with the well, in which the stopper-like tooth of the dactyle fits. It is
bounded by a rectangular process above and a less prominent one below. Tips of fingers barely
overlapping. Dactyle sometimes overreaches propodus. Thumb (or extremity of propodus from
joint of dactyle) one-third to one-half length “‘ palmer portion” of propodus. Dactyle works some-

‘what obliquely. ‘Tips of fingers simple. Propodus sometimes hooked.

Small claw (Fig. 3, Pl. xxrv) usually carried bent downward. Fingers nearly equal; three-
fourths as long as palmer portion of hand; bent slightly downward and outward; propodus sub-
eylindrical ; half as broad as long; tip simple or slightly bifid. Small bunches of set on fingers.

Second pair of pereiopods (Fig. 1, Pl. xxi): The characters of this appendage appear to
be remarkably constant and of considerable specific value. They end in a small claw, the
fingers of which are provided with bunches of long hairs. Carpus superficially constricted into
five rings or segments. First or proximal segment nearly equal to 2+3+44+5. Second, third,
and fourth of nearly equal length; fifth equals 2+3.

The third, fourth (Fig. 2, Pl. xxii), and fifth pairs (Fig. 1, Pl. xxrv) of walking legs are similar
to each other, the fifth pair being shortest. Each ends in a short, horny dactyle which is bifid at
apex, the primary claw bearing a smaller secondary tooth at base. Propodus little shorter than
meros in the fifth pair, and carries numerous bunches of short sete on its under side. There are
also found in this region of the propodus four to six stout appressed spurs.

The first pair of pleopods is specially differentiated in the sexes, and forms one of the most
convenient marks of distinction. The first abdominal limb of the male is shown in Fig. 4, PI.

.XxIv, and the corresponding appendage of the female in Fig. 5, and the typical appendage in Fig.

6. In the unmodified limb the protopodite carries as usual the two branches—endopodite and
exopodite—each fringed with long sete. The endopodite is a little longer than its fellow and
bears a rudimentary secondary branch, which springs from near the middle of its inner edge.
In the male (Fig. 4) the appendage is considerably reduced. The exopodite is short and the
inner branch a small rudiment. In the female (Fig. 5) the modification has not proceeded so far.
The endopodite is here the shorter and has no secondary branch. In the very young forms
(first larve) these appendages appear to be nearly alike in both sexes (Pl. xxu, Fig. 5).

The uropods or sixth pair of pleopods hardly require special notice (Pl. Iv). The endopodite,
much the smaller division, is an oval plate, and on its upper side there is a roughened median
ridge. The free edges of the plates are fringed with long and closely set plumose sete.

V.— VARIATIONS FROM THE SPECIFIC TYPE.

We are now ready to consider the remarkable variations which this species undergoes. The
form just described was taken as typical, and the largest adults invariably belong to it.

(1) Variety Longicarpus: This is the widest departure from the first form or type and is very
commonly met with in the brown sponges already noticed. Probably more than 90 per cent of the

384 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES,

individuals found in them belong to this variety. The color variations of this form have already
been given in section I.

The rostrum is sometimes wanting, as in the individual from which Fig. 11, Pl. xxu, was
drawn. This variation has been noticed in other species and is interesting, since the absence of
the rostrum is a constant character in a closely related series of forms, which are placed by Dana
in a separate genus (Beteus). These variations indicate that the uniform presence or absence of a
rostrum is a specific and not a generic character, as has already been shown by Kingsley (29).
The structural points of difference between the longicarpus and the other form lie chiefly in the
antenne and first pair of walking legs. These may be seen by a comparison of Figs. 11, 13, 18,
Pl. xxi, and Fig. 2, Pl. xxtv, with Figs. 4, 8, Pl. xxm1, and Fig. 3, Pl. xx1v.

In the first pair of antenne the aural spine (Fig. 11, Pl. xxi1) is scarcely more than half the
length of the first segment of the stem. It is blunt and somewhat ovate in shape, as seen from
above.

(2) In the other form (var. brevicarpus) the aural spine (Fig. 4, Pl. xx1i1) has a different shape,
and is relatively nearly twice as long. In this case it extends beyond the first segment to two-
thirds the length of the second. The second or outer antenna of the longicarpus is armed with two
spines at its base (Fig. 11, Pl. xxm1); an inferior and outer basal spine, and a slightly longer one,
the squamous spine, articulated to the joint carrying the latter. Thereis no scale. The basal spine
is rather more than one-half the length of the antennal stalk. There may be present a small
tubercle on the upper surface of the segment bearing the basal spine, near the articulation.

In variety brevicarpus (Fig. 8, Pl. xx111) the squamous spine is stout aud reaches nearly to the °

end of the antennal stalk. There also springs from its inner and proximal margin an elongate
plate or scale, the inner free edge of which is fringed with plumose set; scale not quite as long
as spine. The inferior basal spine not one-half the length of the squamousspine. There isa rounded
or pointed tubercle over basal spine near the joint. ;

The small chela of the first pair of thoracic legs of the longicarpus (Fig. 2, Pl. xx1v) is short
and broad. The finger ends in two or three horny teeth or prongs, which interlock those of the
opposing thumb. The dactyle bears on its outer surface a tuft of peculiar hairs. The latter are
finely serrate and have bent or hooked tips. The carpus is ee very long, quite as long as
the palmar portion of the propodus.

In the brevicarpus the small chela is long and somewhat narrower (Fig. 3, Pl. xxtv). Tips
of fingers usually simple, but sometimes notched; the peculiar tuft of hairs is wanting. Carpus
relatively short ; about one-third the length of the palm. :

The large chela of the longicarpus may also differ noticeably from the brevicarpus type. (Com-
pare Fig. 5, Pl. xxv with the figures on Pl. tv.) Fig. 8 represents a common form of this append-
age. The propodus is long, cylindrical, slightly twisted, very smooth, and polished; ends above
dactyle in a short spine and below in a rudimentary fictuttib with claw- ike tip. Dactyle overreaches
propodus, and its inner margin is not concave, or but slightly so.

These two forms, differing in the particulars just mentioned, would doubtless be considered
as two distinct species if only these facts were known. A prolonged study, however, of a large
number of individuals, collected both in sponges and from porous rocks on a number of reefs, has
resulted in the discovery of a complete series of intermediate links. These connecting forms sug-
gest a number of important questions relating to the causes and significance of variation.

By far the greater number of individuals of this species have the characteristics of the two
varieties just described, but aboutfive per cent of the collection made at different points near Nassau
present intermediate characters.*

More fully stated, the noticeable points of variation are as follows: (1) The relative length of
the antennular stalk and aural spine; (2) the lengths of the antennal spines relative to each
other and to the peduncle of the antenna; the presence or absence of a squame or scale; (3)
the character of the dactyle and propodus of the small chela of the first pair of pereiopods; (4)
the length of the atarDys of the small cheliped ; B) the general shape and character of the large

*While the species live, as a rule, in the interior of iy green and brown sponges, a few undersized individuals
may be found, by careful searching, among the loose blocks of porous.coral which are scattered over the reef, and it
frequently happens that these individuale possess intermediate characters between the two varieties just described,

7s ati al mo ae | ae ; ‘. " ‘ol

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 385

claw. (1) With respect to the first point, we meet with a perfectly graduated series between the
two extremes (Figs. 11, 18, Pl. xxu, Figs. 4, Pl. xxi). (2) The same is true of the relative lengths
of the antennal spines, the scale, and peduncle (Figs. 11, 13, 14, Pl. xx). In Fig. 11 there is no
evident scale and the spines are nearly equal. In Fig. 14 the spines are markedly unequal, and
there is arudimentary scale. In Fig. 13 this seale is further deveioped. (3) Great variation is seen
in the small chela. The fingers of this claw may each end in two or three prongs, or one in two,
the other in three, or the tips of the fingers may be simple or merely notched. The tuft of peculiar
set on the dactyle may be reduced or wanting. (4) Various stages between the long and short
carpus are observed, and (5) slight variations not easily described are constantly seen in the relative
size, shape, and other characters of the large chela. ir

These variations are shown in a general way in Table I. (For detailed measurement, v. Table
II.) The fifteen cases here recorded were selected from upward of seventy-five, in a large number
of which the variable parts were drawn for more careful comparisons.

TABLE I.—Showing variations in Alpheus sauleyi and the intermediate stages between the varieties
brevicarpus and longicarpus.

= |
No. | Sex. Habitat. Length. Aural spine. Squamous spine.
mm.
1 & Green sponge.. .----- 29.7 | Extends } length 2d seg- | Extends nearly to end of antennu-
ment of antennular stalk - lar stalk.
2 Cpl RC Biel a ae Be, [ht 3 To 41, 2d segment.-.-.....-. Do.
31 ieee Brown sponge... ---- Do.
4|_ 2 | Green sponge--..-.-.... Do.
5] @ | Rocks; Dix Pt. reef--. Extends nearly to end of antennal
stalk.
Gate Si 23500) Beadenvceacen= LOC AS | oe ace = do ...-..--.----------| Not nearly to end of antennal stalk.
7 Obed, see Mera an reer eat = 11.6 | 1. of Ist segment. .----.-.-.- Do.
8| fg | Rocks; Hog Id.reef..| 10 | Over 41. of Ist segment --.-] #1. antennal stalk.
9 eel eee ith ee ee a 10 Nearly to end 1st segment..| More than # antennal stalk.
10| ¢ Bopks Green Key 9.5 | #1, Ist segment..---...--.. Nearly to end antennal stalk.
ree
11 g | Brown sponge ....-.. 17.5 | Nearly to end Ist segment-.-| # antennal stalk.
117 ey ia RE SC ee Se corte ihe a ESe ee GOpre. aelata asap ana More than 4 antennal stalk.
13 - Rocks; Dix Pt. reef. - 9.5 | 4 1st segment............-. Do.
14 a Brown sponge -..----- O75 fia 3. OOo Saar aes cee #1. antennal stalk.
15 2 Reef rocks: i-. st-c2 ll Nearly to end Ist segment. -| 3 1. antennal stalk.
No.| Inferior basal spine. . Squawe or scale. Car us of Fingers of small chela. Remarks.
1 | 4lengthsquamous | Scale as long as | Short ---.| Tipssimple; notuft | Type of var. brevicarpus.
spine. squamous spine, on dactyle.
2 | Less than 41. squa- |..-.do ..... sew en as on nO a ato = Tipssimple; notuft.| v. drawing, Pl.1v.
mous spine.
DB lsnckOd wasoae =u ae Scale nearly as |-..do ...-...|.... do ....-...----.| Claws dull red.
long assquamous
spine,
APS Ld sce. apa keene Seale somewhat |..-do ...-..].... Orns oScnee sons
shorter than
squamous spine. .
5 | Nearly 4 1. squa- | Secale not quite 1. | Long.-.---. Tips simple; rudi- | Combines characters of
mous spine. squamous spine. mentary tuft. both varieties.
(6) 255200. s-sescee-eree Smallandrudimen- |.-.do ..---. Prongs; tuft on
tary. dactyle.
7\, 41. squamous apine:|- 2.00) oe eos eeem ol omnis Hawn teenies oe en = mone
8 | $1. squamous spine.| Rudiment -.--..-.-. Short -....| Tipssimple; notuft-.| v. Fig. 13, Pl. xx11.
a eee eee teenies <ice OO) etemaw ace sear) OD Pa. sac- Prongs and tuft....| v. Fig. 14, Pl. xxu, (outer
antenne from above).
10 | More than}]. squa- | Rudiment (hardly |...do ...-. -| Propodus ends in | Dactyle missing.
mous spine, visible). prongs.
1 Ml ee Ree Gp eeteas Rudimeng <..22..-|-. do .22_-- Prongs and tuft....| Claws reddish orange.
1 ee one Dias ters NG BORO co et ay eee en UO deere | Se O) ooo seco e as cs
1k 9] (7 oe ee BS REE olin SAG el ie oa CU ape es Type of var. longicarpus.
14 | Nearly as long as |....do ..+.....----.|..-d0 ..... a) QeRe Ce ere eae Rostrum wanting.
squamous spine, | ~
ieee | pee io re niciea ee i gs Easton ie Rea 9 | EY Cn a WeweQOlpausuce suena Claws bright blue; dactyle
of aa chela extends
1™™ beyond propodus.

S. Mis. 94-25

386 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

In Nos. 1 to 4 we find little variation from the brevicarpus form, which we consider as nearest
to the type of the species. From No.5 to No. 15 the departure from this type is increasingly
evident, and in Nos. 12 to 15 we recognize the widest divergence in the varity longicarpus.

No. 5 is an interesting case, since it combines the characters of both varieties. The aural
spine is rather blunt and extends to one-third the length of the second segment of the antenular stalk.
The inferior basal spine is rather less than one-half the length of squamous spine; upper basal spine
a rudimentary knob. The squamous spine has a well-developed squame; nearly equals length
of antennal peduncle. The “finger” and “thumb” of small chela end in simple, sharply pointed
hooks. There is an inconspicuous tuft of sete on the dactyle. The carpus is long. (See Table IT.)

No. 8 is also an interesting variation. The antennze are intermediate in character, between
the extremes of the table, while the small chela is of the brevicarpus type. There is a rudimentary
antennal scale. The tips of the small chela are simple. There is no tuft, and the carpus is short.

In No. 9, which is of the same sex, the same length, and from the same locality as No. 8, the
small chela has the characters of the variety longicarpus. Nos. 5 to12, in the middle of the table,
show in one way or another intermediate characters between the extremes, Nos. 1 to 4 and Nos.
12 to 15,

VI.—MEASUREMENTS IN MILLIMETERS.

TABLE Il.

[Locality: Nassau, N. P., Bahama Islands.]

: Rocks:| Rocks: Rocks: Rocks

. Green | Green |;)- 35 a ia) Fis | Brown |7,-
BEAR es 229 2992008 soo Sasson aaa aa gaia spouge.|sponge. a Grae Fey Rrer eek sponge. Tee
SEK ee wa ae ee mr 94 rofl 2 c 2 2 g
INump er eta le enn. seese= sehen ee eee eee eee 2 1 10 6
Length (tip of rostrum to end of telson)......---. 42 29.7 | 16 9.5 10.4 | 11 21
Length of carapax, including rostrum... .-...-.. 15 11 7 Gale Rees 4.4] 4.5] 8
Greatest width of carapax.-.---...--..---..-.--- i Pe hae 4) te eeatees ZrO il ies kel) D
Greatest depth of body-.---- -.---...-...-......-. lee Ses oe eR Bh Se Bi thine Sho) eee
Distance between ocular spines..-.-..----.---.-- Cae a eel? 6) REN) ee We = Fee re | Sts So] See
Breadth of second abdominal somite ...--.---..--- a oa eee on senso Pease A at Sis 5a eel hae
Depth of abdomen (with ova) .----..---..--..---- 15. 4|-2-22 [ee soos) See ean eee ie ee See eee ee
Length of terga of abdominal somites in median

line:

Hirsh berSaM % 32 -oe wc) ee new one nee 2 END llaSe 2 oa aeeeltewe | aana at al] eel es

SOAS Gl ee or cootc JHB ee DBs cadosee easea ces G22 |) $258) <= PAB ee a er eee ee

(Ui til pee Sores Se ces Sseeeo rescce cee Steet De) See Sete ee ceen| Sacce cee a eee eee eee

LOHR ween Aion g Chao) capaercce sso ete ces ye el TG (ae (eel net eae Sie fee el BE Se

LHe Ra Sh SO Ss sea sboste Soa cae 4 220) Poco s| | ower rato |e eee eee ere

STR Gee omccedn - cdo cee ssp etee co ttaced Sine 3.8]! (a6 |. onkine- =m es [ eae Sees | meee eee ee
enrthtofmelsone.. sec eee=s ese eee eee 5.00) AM Nocti b aoe es eee es | eee eer ane
Breadth of telson at base. ..-....----.-.----.----. 4 Ce Jel eens sees sec Pers rele sep fee eras) = Ste.
Breadth of telsonsat tip] io-- 5 <. co nec eee coe 2 RR ree esse eno eees|\asel sss 3
Length of antennular stalk .........-....--.. -.-- 6 Dae le re 1.8 18) 109") Ska
Length of antennular segments :

LOM oss Sose Scams cosese cree ees Fo OCS E Sos aS 3 2.2] 0.9 VES Sea ore 1 2

Shirl AR Ie ee Sere amectan.Sanenoro sees 2 Pane Pee say eee Se oo arBo sere ecm ccn| asec

AW Tye be ao eo ssecoe Dose She 1 1 Sen of See see ee | ee Saal eee oa ee
Breadth of first antennular segment--..---...---- 1H Boa lee woesct| eee eat |eeseseeerl sane mel aeees
Length of antennular or aural spine-.....----.-.. 4 BE ml pel 0.7 A aah Ve 233
Widthiofisamerat basen a. a=. 2. a5 nem eeoceae NO eres Bere) |tace eesal|pecee on sal baee sheer sos
Length of exopodite of antenvule.............--- 6 rte a aa 2. 0b Waar ete eS ae
Length of endopodite of antennule- .--....--.-.-- 9 10) aifeeaae S| eee ae Bri leases
Length of antennal stalk. ....-.....2.-.-.-----.-- 6257] SO Silene ee 1.5 LEG nase O gt}
Length of long segment of same ..-.--.-----.---- 45,6) 1S COAG Gal ere ere | eer eee eee eal ee
Greatest width of long segment-.-.--....--..----. 1 a ee RL ee pee be Ses 2S GE ye aS ao Se
Length of squamous spine.......----.------.----- 4.7) 4 1.4 1 TE Ct isa
LORSTVEG |S cep ene OR ee ap ne Set et oe 5 HBS ee aha S55 Dele Cees 1.9
Width of spine and scale at base.----..----.----- 1 ES BR Ae ES el ani eee s(t aa (ei
Length of inferior basal spine...-....-.-.-------- 2.2) 2 0.9 0.8 Bie Biche ise =
Length of superior basal spur: - === -2 2-22-28 22-2) 0.3 |) O24 eeee en eee ah oe oie oae| onan eee
Width of basal segment: -- 222-2. 22.2022 2s ek Ue Sal ne AS (eee: Sea PEGs ees le setes)| “sn Se-
Length of same to articulation of squamous spine} 2.0 |...---|------|---------|---------|-.----|------
Length of flagellum ........--. Soveue cen eae de omes 16 15) ease se SEM (ssgencse 5.8] 7

ie [eee ST eer ee

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 387

TABLE 11—Continued.

(Locality: Nassau, N. P., Bahama Islands. }

~ l. |Rocks:| Rocks: | Rocka: Rocks:
Green | Green "IR > ~ > Brow :
Ot Eee ees OPP a ece Meeer Poy ee -- |sponge|sponge.|Pix Pt-|Green Key|Green Key lsponge. Dix Pt.
- — ~ - - |
[3 vs ESE oe eae ee ee eee eee 8] roa 9 f fe) ood DA:
AVRO SN Int CER DIE rosacea lo nna. wi och ae dcnstw ives ceaee ue ine tes 2 1 10 6
Length of propodus of large chela .......-..-.----- 15 at | santos : Bait 4.5| 6 BK!
Length of same to spine at base of dactyle.....--- 11 11 5.1 4.4 ea | ee eR st
Greatest width of same .......--.....----5.----- SeGi inated. |ooe Ben Pats) 2 ye (El as
Greatest uepth ofsamie -fe!ls 2.2 i225 85 4 BG | eee eee 4 2 2
Width of same at spine, at base of dactyle....-.-. rial ey, We eee Dae A eetendecualosaseelesotec
Length of ‘‘ thuml ” of propodus. ...-.....--.---- eg Stel ae | Se onl eee
° PenpihOnagey lec. cse<\.c once csecee ce Sets ess 4 6 2 2 1 Pie ee
Width of same, over tooth ...-.....---...--..---- 3 Cn Ber 1 pioneer &) Peet ry) ener
Length of carpus of large cheliped, on upper me- ;
Me Gees alec ome Satin sacs anea ns eae ec 2.6) 2.4
Length of meros of same. ..-.......-..----..----- 5.5] 5.3
Greatest width of meros of same..........-...---- 3 2.6
Length of propodus of small cheliped-....-...---.. OA eG
Length of same to articulation of dactyle-.-...--.- 4 3.1
Greatest width of same -22--.<2o5-6.2. 2.2 2 2.4| 2
Greatest depth of same -.-..........---......--.- 178) eee
Length of dactyle of same ........---..---------- Br or es
Width of dactyle of'same <7. --..........2-..-.---: 1 0.9
Length of carpus of same .-......---....-.. -.--.] 2.3] 2
Length of meros of same. .--.-- Sere ae 6 5
Greatest width of meros of same....-..----..----- 2.7 | 2.5
Length of carpus of second pereiopod..--.--..-.--.- 7 5.5
Length of first segment of carpus of same -...---- APA ee eres c's
Length of fifth segment of carpus of same --------| 1 |...2..|..----
Length of second, third, and fourth segments of
GATPUR OL SANG Reena ois on eco esan ss sue desice~ s.2= 5 ee ee Sheree oa eee ites dle at oo ole ces lien ae oe
Length of propodus of same..---.---------------- DoW ig a[ sae ate 2 1 1 UR ssc
Length of meros of same-...--...-..-----.-------- HAN eer a (SS 2 a A oP eee eee cei c
Length of propodus of third pereiopod ..-.--.--..- 5 LAS |: Sy Ee SS Se) AOS 8 ee
Length of carpus of same...-...-..-.-----.------ Deen eney feaeee = fase eenaee | senerstnesi| somata! omereme
Length of meros of same. ..--...----.------------ Grdelie. Os ilps | oes Sabet tepow see's [eecee an ae
Length of ;,rotopodite of third pleopod....--. ---- 6 Udine = | Oe Ses es BES Bar nee eee
Width OP Bam: fo oee tence an aes eeehacaas vocee= =e TA \6e8T is Le e ME el ae SS ee ey Pee
Length of endopodite of same-...----..----...----| 8 Cena Ns 1c] Re ee ol |S ease Boece
Greatest breadth of endopodite of same ...--.-.--. Le | EL ERAS oe eat ara eS et a eS
Length of exopodite of uropod....-..-----.------ Gaye ro Tt EN OO Se oe Ser ee ceee Mesricc
Breadth Of samess-s-apasnsseeeoetean ses sencee ADA Lh Caliteceae| = 24 Ste oy | see npn|se seal aseas
Length of endopodite of uropod ...-- aerate te 5 Uedilseeeeel cea scees len ustaval ue scce| mone
Breadth of same? seca sasee snes - sence ss watiec se 3.5-] 2.9 | Be ee eet ocaee lc cow davies | tekae| meee

VII.—THE CAUSES AND SIGNIFICANCE OF VARIATION IN ALPHEUS SAULCYI.

If we consider Nos. 1 or 2 of Table I as representing the nearest approach to the mean of the
species, Nos. 5 to 15 must stand for individuals which have fluctuated farthest from the mean.

The individuals given in the table were chosen without reference to sex, yet it appears that
nearly two-thirds of the number are males. In examining a larger collection of these aberrant
forms | find a still greater percentage of males. There can be little doubt that in those cases the
males are in the excess, although I have not tested this point carefully. It is also evident from
observation and detailed measurements that the average size of these abnormal individuals is less
than one-half that of the brevicarpus type. The brown sponges teem with a population of under-
sized forms, nearly all of which are aberrant, and none of those which were examined exceeded
the length of 17.5", which is considerably less than the average for the type.

How far are these variations individualistic and how far are they confined to the race or
species as a whole? In other words, is the individual plastic, departing from the standard of the
species and becoming different at different periods of its life, or do individuals deviate from the
jean of the species, each along its own line? Further, are the variations congenital? While we

388 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

are not prepared to answer these questions as fully as we could wish, yet the facts are sufficient
to throw some light upon the subject.

We have abundant evidence that there is considerable fluctuation in the life of the individual,
as regards the number, color, and shape of pigment cells for instance. In all larve of these prawns
the external antennz have a well developed scale, and it is thus clear that this organ may degenerate
and apparently disappear, to be reconstructed again at alater period. The variety longicarpus (No.
15, Table I) has no *‘squame,” although it is present in the young (Fig. 7, Pl. xx11), and the cases in
which the organ is seen in various stages of development (Figs. 13, 14, Pl. xx11) support and illus-
trate this conclusion, This, however, is not a rule with the species as a whole, as it is in the some-
what analogous case of the loss and subsequent reconstruction of the last two pairs of thoracic
legs in the larvze of Stenopus and Sergestes.

The question as to how far the characters which distinguish such forms as Nos. 1 and 15, Table
I, are congenital can only be answered by a careful study of their development. My attention was
not directed to this subject while at the seashore, and in this connection some interesting experi-
ments remain to be performed. The evidence we have goes to show that the young in any given
case share the peculiarities of the mother, and this is probably true of such details as the right and
left handed condition of the large chelipeds. The following examples iJlustrate this fact: (1) The
adult female in this case has the characters of No. 15, Table I. The antennular or aural spine is
nearly three-fourths the length of the first antennular segment. The aural spine has a correspond-
ing length in the larve of this prawn at the time of hatching. In the adult the fingers of the
small chela end in prongs; there is a tuft of peculiar setz on the dactyle. In the first larva the
fingers of the small chela also end in prongs, and there is a tuft of rudimentary setze on the dac-
tyle. In the adult the carpus of the small cheliped is relatively very long. In the first larva the
carpus of this appendage is about one-third the length of the propodus (relatively a little shorter
than in the adult). Fig.11, Pl. xx11, may be taken to represent the mother (rostrum here wantirg),
and Fig.17 the young. The small chela of the mother is shown in Fig. 2, Pl. xxiv, that of the young
in Fig. 15, Pl. xxu1. Another case exactly like this was observed, where the embryo was taken
from the abdomen of the female. (2) The adult in this case has the characteristics of No. 2, Table
I (var. brevicarpus) (Pl. Iv, Figs. 1,2). The larvee are shown in Pl. xx1, Figs. 1, 2,3,8. The aural
spine, at first short, is nearly as long as the first antennular segment when the larva is a week old
(Fig. 10, Pl. xxm). In both the parent and young the carpus of the small cheliped is relatively
short. The fingers of the small chela end in simple tips; there is no tuft on the dactyle (see
Fig. 16, PJ. xx11).

These facts indicate that the young share the peculiarities of the parent, but exactly how far the
individual may depart from this standard in its own life, or how strictly the law of inheritance
applies in all cases, my observations do not warrant a decisive answer. A few experiments could be
easily made upon this Alpheus which would throw light on some inteiesting questions in heredity.
The females with ova are easily obtained; the young are readily hatched and kept alive in glass
dishes until they have reached the adult state.

In this species the change of environment, due to the adoption of life in Sponges, has probably

_acted as a direct stimulus to variation. These animals tend to vary most along certain definite
lines, as, for instance, the relative lengths of the antennular segments and aural spine vary much,
while those of the segments of the carpus of the second pair of thoracic legs are practically invari-
able. Homologous parts vary alike, unless specially differentiated in different ways, as in the
chelipeds. There is no diversity of life between males and females, and both sexes vary alike, but
aberrant males are probably the more common.

The oceurrence of large numbers of individuals showing variations of the same ‘kind, but of
different degree, render it plausible at least that the same variations may occur in a large number
of individuals simultaneously, but the reason why this or that part has varied most is wholly
obscure. ; 5

The aberrant forms (variety longicarpus) which have adapted themselves to life in the brown
sponge thrive and produce young which, in the early stages certainly, share in the peculiarities of

the parent. The variety brevicarpus is similarly adapted to its environment and its young resemble ~

We i ie OS. ek? >. aie ra aes : >, 2

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 389

it. Has natural selection, then, acted so far as to differentiate the species in more than one direc-
tion? There are some facts which favor the view that it has done so, but before the question can
be definitely settled we must determine more precisely how far intermediate or aberrant forms
represent phases of the individual and of the race. It is not probable that we are here dealing
with the hybrids between two originally distinct species.

PART SECOND.
THE DEVELOPMENT OF ALPHEUS.
I. STRUCTURE OF THE LARVA.
(Pl. XLIX, Fig. 174. Pl. rim, Fig. 196. Pls. Lrv-Lvt1t.)

These studies in the embryology of Alpheus begin with the growth of the ovarian egg and the
early phases of segmentation and extend to the larval and adult periods. In order that the prog-
ress of development may be followed in the light of the structure which the embryo finally attains,
we will start with a general survey of the anatomy of the first larva of Alpheus sauleyi. A fuller
description of the histology and histogenesis of the tissues will be given in the parts which treat
of the different organs in detail.

A profile view of the larva as if appears while still inelosed by the eggshell and of one imme-
diately after hatching is seen in Pl. xx1, Figs. 1 and 5, and the brief and insignificant metamor-
phosis which is required to provide it with the adult characters are illustrated and described in
a separate paper (Pls. XXI-XXTv).

Most noteworthy are the large, stalked, compound eyes, the segmented abdomen provided
with its full number of appendages, the short, stumpy antenne, and the swollen chele or pincers
of the first pair of thoracic legs. At this stage this Alpheus is a larva, but in a restricted sense,
since many adult characteristics are present. It is a larva, with preparations for immediately
assuming the adult state. Some of the larval peculiarities are the spatulate telson, the biramous or
schizopodal pereiopods (first to fourth pair, inclusive), the radimentary pleopods, the unabsorbed
foed yolk, and the uncovered, stalked eyes.

. The structural details are now very great, so that it is often impossible to interpret the parts
seen in a single section, and it is only by comparing sections made in different planes that the
relations of the organs can be successfully made out.

In Fig. 196 (Pl. Lim) the plane of section is nearly vertical and median throughout, except
for the posterior halfof the abdomen. The supra-cesophageal ganglion, which is usually spoken ofas
“the brain” (8.0. g.),is a complex organ, composed of internal, medullary masses( punktsubstanz balls),
and cellular tissue which completely invests them. It is made up of the fused ganglia of at least
two segments, those of the first and second antennz. This fusion is complete from the early stages
of development, and the relations of the parts are now extremely complex. They are best illus-
trated by a comparison of the series of transverse sections (Pls. Liv, LV, Figs. 211-219) with
those made in a horizontal plane (PI. Lyi, Figs. 238-243), and it will be seen that there are four
pairs of fibrous masses in the brain, intimately connected together.

These compact and finely granular masses in the interior of the ganglia of invertebrates were
described by Leydig twenty-five years ago under the name of Punktsubstanz and later by Dietl
(1876) as Marksubstanz. As Krieger remarks, the latter name is bad, since it confuses this tissue
with the spinal marrow of vertebrates, with whieh it has nothing to do. It is essentially a /elt of
very fine fibers. We will therefore speak of it as the Punktsubstanz, or, to use a more descriptive
term, the fibrous substance of the ganglia.

The first pair of these, the anterior or optic fibrous masses (Pl. LV, Figs. 212-215), are the
largest. They are completely fused on the middle line and form a single compact mass, which is
slightly constricted laterally (Pl. Lym, Fig. 242, of.) and which is divided in front (Pl. Lry, Figs.
210, 211), where it gives off two diverging stems of fibrous tissue (sometimes called optic nerves) to
the optic ganglia in the stalks of the compound eyes (see also Pl. Lvu, Fig. 240 of.).

390 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Next in point of size are a pair of large lateral balls, which appear kidney-shaped in transverse
section (Pl. Lv, Fig. 216,1.f.). Hach is virtually segmented at the lower surface into two lobes (Pl.
Lvu, Fig. 242, l. f.). These lobes are closely united to each other, and by a pedicel or stalk of
fibers to the lower posterior extremity of the anterior, optic mass. A third pair of fibrous masses
(Pl. Lv, Figs. 215, 216, af.) fuse with the anterior mass at the same point. Each of these balls
is also bilobed, and from them issue the fibers of the antennular nerves. (Pl. Lyn, Fig. 243, n.
au., also Pl. LV, Figs. 212-214, a. 0., nau.) The nerve of the first pair of antennz consists of
cells and fibers, which pass to a mass of deeply staining cells (a. 0.), the ear, and to the tissues of
the antennular stalk. The fourth pair of fibrous masses (Pl. Ly, Figs. 217, 218, gf., also Pl. Lv,
Fig. 243) are intimately associated with the last and with the common bridge of tissue (Pl. LV,
Fig. 216, of.) which unites them all. From these arise the fibrous elements of the antennal nerves,
which supply the green gland and the tissues of the appendage (Fig. 216, n. ag.). From this
same region (Fig. 218, fo.) the commissures which surround the esophagus and unite the brain to
the ventral nerve cord also originate (Fig. 220). These commissural bands meet immediately
behind and below the esophagus, where they fuse (Pl. Ly, Figs. 222, oem.) and join the ventral
chain of ganglia. This last consists of the ganglia of the remaining eighteen segments of the
body. Each ganglion is double and is made up of two fibrous balls, united by a transverse
commissure, and of a thick envelope of nerve cells. Longitudinal commissures of cells and
nerve fibers unite the successive ganglia, which form a doubie chain. These relations are well
shown in Fig. 196 and by the horizontal section (Pl. Lv, Fig. 243). The first six thoracic ganglia
are very closely crowded together (Fig. 196, g. 4-9) and form what is usually known as the
infra esophageal ganglion (ganglia of mandibles, first and second mavxillz, and first, second, and
third maxillipeds). The next five ganglia, g. 10-14, which are less closely crowded than the
preceding, belong to the five pairs of thoracic legs and their segments. The fiber balls of each
ganglion are pear-shaped masses, disposed vertically, with the large end of the pear turned toward
the base of the appendage. The abdominal ganglia are more widely separated and the longitud-
inal commissures are consequently more marked (Iig. 196, g. 15-20; see also the series of trans-
verse sections, Pls. LV, LVI). The nerves, always difficult to distinguish, owing to the close
similarity of their cells to those of the surrounding ectoderm, are best exemplified in the case of
the antennular and antennal nerves already mentioned.

The relations and course of the fibers, which are very complicated, are partially indicated.in
some of the sections. There is a marked transverse commissure of fibers in the anterior half of
the large optic swelling (Fig. 213), and at its posterior extremity, where it fuses with the lateral
and antennal masses (PI. LI, Fig. 198, gf).

The optic stalks or lobes, bearing the compound eyes (Pl. Liv, Figs. 209, 210, and Pl. Lvu,
Figs. 239-242), consist.of an irregular series of fibrous masses, in shape of a distorted letter L.
The angle of the letter L is continuous with the fibrous substance of the brain, while its shorter limb
proceeds to the compound eye and its longer forms a large swelling in the upper part of the stalk.
There is a nauplius eye (PI. Lin, Fig. 197; Pl. Liv, Figs. 209, 210, oc.) borne on a median papilla,
which projects downward between the eye stalks. The details of the structure of the eyes are
given in Section Ix.

The alimentary tract of the larva is a somewhat complicated structure, and the relations of its
parts are best understood by reference to sections taken in more than one plane. We can recognize
five well-defined portions: the esophagus, the masticatory stomach, the midgut, the hindgut or
intestine, and the appendages of the midgut. These are shown in a semidiagrammatic way in the
cut (Fig. 2), and the longitudinal section (PI. Lin, Fig. 196) and series of transverse and horizontal
sections (Pls. LV—LV11) illustrate the structures in more detail. °

It is interesting at this point to compare the larva shown in Fig. 196 with the longitudinal
section of an advanced embryo (Pl. XxLvul, Fig. 168). In both we recognize the foregut, a tube bent
on itself, consisting of the esophagus and masticatory stomach (m.s.). In the embryo the latter is
closed on the side of the food yolk. In both we also see a vertically directed fold of endoderm (/,,
overlying mg® in Fig. 196) and behind this the large lumen of the hindgut, which gradually tapers
into that of the narrow, tubular intestine. Between this fold on the one hand ard the stomach on
the other we find in the embryo an enormous space filled with yolk, which is partially walled in

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 391

with endodermal epithelium near the point where it communicates with the cavity of the gut.
This in the larva corresponds to the midgut (Fig. 196, mg.) and its diverticula.

The w@sophagus (Figs. 196, 218-220) is a straight, vertical tube, with very thick walls, which
are thrown into longitudinal folds. There is an anterior and posterior fold and two lateral ones,
which give to the lumen of the @sophagus the shape of the letter X when seen in transverse
section (Pl. Lv, Figs. 241, 242). The walls of the masticatory stomach resemble those of the
csophagus, and the folds of the latter are continuous with the valvular stractures of this region.
The lateral and median thickenings (Pl. LV, Fig. 221, p. v.) at the point where this portion of
the stomach passes into the midgut may be regarded as a rudimentary pyloric valve. The pouches
formed between the median ventral fold (Fig. 221) and the lateral folds (p. v.) correspond to the
gastrolith sacs in the crayfish embryo (54), but no gastroliths are found in Alpheus.

The midgut appears in the longitudinal section (ig. 196, mg.) as a short, restricted cavity.
It is, however, a spacious chamber, as we see by examining a series of sections made in other planes
(Pls. LV-Lvu). It consists of seven parts or divisions: a dorsal, unpaired, median division (mg.
in all the figures), and, opening from this, a pairof anterior lobes (mg.'), a pair of posterior (mg.")
and a pair of ventral lobes (mg.”). All these parts are lined with a peculiar columnar epithelium,
composed of endoderm cells, derived primarily from the wandering cells, excepting a part of the
median and the anterior divisions, where the endodermal wall is absent or only imperfectly formed.
The epithelium of the midgut passes imperceptibly into that of the intestine, since the cavity of the
hindgut is in communication with the food yolk from the very early stages of the embryo, and
since also the endoderm is formed very gradually and first appears in the region where the hind
gut communicates with the yolk. On the other hand, the demarcation between the wall of the
masticatory stomach (of ectodermal origin) and that of the midgut (Fig. 196) is most pronounced.
Correlated with this distinction is the fact that the foregut is a blind sac and completely cut oft
from communication with the yolk until very late in embryonic life (PI. xiv, Fig. 168). The
anterior lobes contain the remnant of unabsorbed yolk (Figs. 218, 237, y.), and in cases where the
lining epitheliam is unformed, the food yolk is in contact with the brain. These lobes are sepa-
rated by a median vertical partition (mp.), composed of connective tissue and muscle cells, which
suspend this portion of the digestive tract to the anterior dorsal wall of the body. In a very late
embryo which is about ready to hatch we find that the partition separating the anterior lobes is
incomplete. The dorsal half of it consists of a downward-growing fold of endoderm cells, with a
mesodermic core. The ventral and lateral walls of these diverticula are devoid of epithelium, so
that the endoderm extends itself most rapidly forward, on the dorsal median line, and thence spreads
to the ventral floor.

The posterior lobes (mg.*) are the first to develop (see Pl wt, Fig. 185, mg.*). They lie to one side
of and below the hindgut (Pl. Lv1, Figs. 226-230, mg’., gg.'“). Up to this stage their position is never
dorsal to other parts of the digestive tract. It is from these lobes that the gastric gland or so-called
“liver” arises. Each lobe is simple until a short time before the embryo hatches, but in the newly
born larva it is divided into three lobules. This division is effected in this manner: The lower
median part of the primary lobe (Fig. 228, gg.') is constricted off by the growth of a fold from the
side next to the hindgut, downwards and outwards, to form a secondary lobule (gg.2). By the
constriction of the upper portion in the same way the primary lobe becomes divided into three
pockets. The relations of the posterior division of the midgut to the unpaired central portion is best
shown in a horizontal section (Figs. 236-238). It seems quite probable that a part of the epithelial
lining belonging to the enlarged section of the hindgut is endodermal in its origin, but just how
much it is impossible to say.

The ventral lobes (Fig. 224, mg.) are ventro-lateral diverticula from the central portion of the
midgut and are completely lined with columnar epithelium.

An examination of the structure of a young Alpheus of this species, ten days old, throws much
light on the anatomy of the larva just considered. The alimentary tract has at this time essen-
tially its adult structure. The gastric glands open into it by short ducts at a point just behind
the masticatory stomach. They consist of three pairs of lobes or execa. One pair, corresponding
to the posterior division of the midgut (Fig. 226, ng."), is imperfectly divided into three lobules,
as in the early larva, They extend backward, below and to one side of the gut. The two remaining

392 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

pairs pass forward on either side of the masticatory stomach to a point about on a level with the
first maxillary segment. The ventral is the larger and longer of these, and two lobules are con-
stricted off from it near its extremity. They correspond to the ventral lobes of the midgut (mg.?
cut, Fig. 2). The dorsal pair represent the anterior lobes (mg.'), which are now entirely withdrawn
from the head region, and naturally contain no food yolk. The gastric ceca are all filled with a
coagulable fluid which stains feebly in carmine. The gastric epithelium for a short distance behind
the point where glands communicate with the stomach has marked histological peculiarities. The
internal absorbent surface is increased by folds which nearly obscure the lumen of the tube. The
cells are columnar and resemble the glandular cells of the liver and probably have the same origin
as the latter. In the masticatory stomach there is a strainer of hairs developed on the ventral
and lateral walls which are greatly thickened, as we saw in the larva. The dorsal wall is thin,
but there is a large valvular fold on the ventral side.

The vascular system of the adult is already outlined in the larva in all its essential character-
istics, The walls of the blood vessels are exceedingly delicate, so that it is not easy to ascertain
their distribution by means of sections alone. The heart (P]. Lu, Fig, 196, H.) is a short tubular
chainber, flattened between the dorsal body wall and the enlarged section of the hind gut. It is
suspended in the pericardial sinus (p. s.) to the body wall and surrounding organs by means of
strands of connective tissue (alz-cordis). The walls of the heart are quite thin, and its cavity is
partially divided into three compartments by the growth downward from its roof of two sheets of
mesoderm cells (Pl. Lv1, Fig. 231, and Pl. 11, Fig. 186).

Of the several arteries which lead from the heart, three, and possibly five, can be distinguished.
Posteriorly the heart is continuous with the large superior abdominal artery, which traverses the
abdomen close to the dorsal wall of the intestine (Figs. 196, 232, 235, a. s.a.). Near its origin
from the heart, the sternal artery (Fig. 196 shows a trace of this vessel between ganglia 12 and 13,
to the left of pr.) is given off, and passes directly downward to the ventral nervous system, which it
penetrates at a point between the third and fourth thoracic ganglia. This is continued backward
under the nervous system and forms the inferior abdominal artery (Figs. 229-234, a. i. a.) Anteri-
orly the heart gives off the unpaired ophthalmic artery (Figs. 196, 215-229, op, a. op.), which runs for-
ward to the region of the eyes and brain. It is not an ophthalmic artery, strictly speaking, but from
the first, supplies arterial blood to the brain and anterior cephalic region generally. In Figs. 215,
216, it is seen cut in partial longitudinal section, where it evidently communicates with the blood
space surrounding this part of the brain. The antennal arteries can not be clearly distinguished
in sections, but in a much earlier stage trains of cells are seen atthe surface of the egg passing
forward on either side of the middle line toward the eye stalks, which possibly represent the anten-
nal vessels.

Besides the sinuses already mentioned, there is a large sternal sinus (Fig. 196, sts. s.). This
occupies the extensive space between the thoracic ganglia and the alimentary tract and “liver,”
and, like all other similar spaces, is more or less completely filled with serum and blood corpuscles.

Five pairs of gills are present at this stage. They are developed from simple pouches or folds
of the skin on the bases of the thoracic appetdages (Iigs. 193, 230-233, br >°). The outer sur-
face of this primary fold soon becomes divided into a number of secondary folds or gill plates, and
in a larva which has moulted twice and is twenty-four hours old, the branchia has the structure
shown in Fig. 195. The adult gill is precisely similar to this, except that it has a greater number of
plates and more definite branchial vessels. In the early larval stages the skin and especially the
branchiostegites (Fig. 193, bg.) probably serve as important respiratory organs.

In respect to its muscular system the first larva appears to differ but little from the adulf.
The flexor and extensor muscles of the abdomen are most prominent (Fig. 196, mu. f., mu. e.). The
former consists of a double rope of fibers, fuse 1 completely together aud very much twisted. They
extend from the sides of the thorax to the terminal telson (Fig. 227-235, mu. f.). The extensor
muscles (mu. e.) are smaller, but otherwise similar to the latter, both in origin and extent. They
lie above or to the sides of the digestive tract. Their attachment to the carapace is shown in
Figs. 227, 228. : ; :

The next most prominent muscles are the adductors of the mandibles and great chele. The
former consists of a large band of fibers which pass from one side of the body to the other directly

+ a>

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 393

over the nérvous system (Fig. 221, ad. m.). Closely associated with it are the muscles of the
maxille. The large flat tendon to which the adductor muscle of the forceps is attached, is well
developed at the time of hatching. Itis formed by the infolding of a sheet of ectoderm cells at the
point of articulation of the fingers of the claws, and in a plane at right angles to their plane of action.
The outer ends ofthe cells of this infolded sheet now oppose each other and secrete the chitinous
tendon, while to their morphologically inner ends the muscle fibers are attached.

The connective tissues invest the organs and seem to bind them together and to suspend them
to the outer ectodermal wall of the body, but in some cases the ectoderm of the surface is apparently
replaced by mesoderm cells, and often muscle fibers appear to be attached to the tergum of the
somite (Fig. 196). This may be explained by the intimate fusion of the ectoblast and mesoblast at
these points.

The green gland (PI. Lim, Fig. 198, ag.) at the base of the second antenna is a well-defined
structure. It consists of a blind tube, which passes up close to the brain as far as the anterior sacs
of the midgut, and of a solid, disc, shaped body. The walls of the tube are composed of a single
layer of large cubical cells. These thin out at the lower end, and to the outer wall is applied the
solid nodular body. Neither at this stage nor at any previous one have I been able to detect an
opening to the exterior.

In the adult the tubular portion of the gland grows to very great length, coiling itself in all the
available space in the anterior region of the body in front of the mandibles. It surrounds the brain
and esophagus and passes down to the labrum and into the eyestalks. The solid almond shaped
body (probably the end-sac) becomes a spongy mass of tissue. Its function is plainly different
from that of the epithelium which forms the wall of the tube and to which the secretive product of
the gland is due.

The reproductive organs, or what I regard as such, are difficult to find, owing to their very
rudimentary condition. They consist of a small cluster of large cells on either side of the middle
line between the digestive tract and the anterior end of the heart (Stage x, Fig. 173, R. O.).

With this sketch of the structure of the larva we are ready to trace the histery of develop-
ment from the earliest stages and to ascertain the manifold changes through which the unicellular
egg with its great store of yolk passes, before it attains to the wonderful complexity of the larval
and adult forms.

Il.—THE ORIGIN OF OVARIAN EGGS IN ALPHEUS, HOMARUS, AND PALINURUS.

(a) Alpheus.—The ovaries of Alpheus are paired cylindrical bodies which extend between che
alimentary tract and dorsal blood vessels, from just behind the eyes to the end of the third or
fourth abdominal somite. Owing to the transparency of the skin in this species (A. saulcyi) they
are extremely conspicuous, giving to the female an intense green or yellow hue, according to the
color of the egg (Pl. Iv). The oviducts open in the usual way by means of a slit-like valve on the
basal joint of the third pereiopods.

In Pl. xxvi, Fig. 11, the condition of the adult ovary is shown, as it appears two or three days
after the eggs then carried on the abdominal appendages had been laid. The ovarian ova are
ripe by the time the young are ready to leave the shell, and the new ova are laid in a few hours
after the hatching of the larval brood. Thus there is a constant snecession of young, and females
are not commonly found without either attached or large ovarian eggs. The breeding season of
this species extends, as we have seen, throughout the entire year.

The structure of the ovary is quite simple (Fig. 11). It is essentially a sac lined with ger-
minalepithelium. The external layer of the sac (O. W.) is muscular and contains numerous nuclei.
Between the epitheliam and fibrous coat there is a wide space filled with blood. This may be
unnaturally Jarge in the preparation owing to the disturbing effects of the reagents employed,

_ but it is not wholly abnormal. The germinal epithelium consists, for the most part, of a single

layer of large cubical cells. The nuclei are large and granular, and the cell outlines are often
distinct. The function of these epithelial cells is twofold: (1) They give rise to ova; (2) They
form the epithelium of the egg follicle. \

There is no germogen or polynuclear mass of protoplasm from which the ova are developed,
but the eggs appear to originate directly from epithelial cells. The new eggs begin to develop,

394 MEMOIRS Of THE NATIONAL: ACADEMY OF SCIENCES.

while the ovarian lobe is yet crowded with ripe ova ready to be laid, on the ovarian wall next the
middle line of the body. The process seems to be as follows: The nuclei of the cells of the ger-
minal epithelium increase in size along a certain tract. The cells grow rapidly and are slowly
dehisced or pressed into the cavity of the sac. Hach is surrounded by a coat of follicle cells.
This is formed by the ingrowth of the germinal epithelium about the egg. Sometimes several
ova occupy & Common pouch (Ger.) which is separated from the rest of the ovary by sheets
of follicular tissue (F. E.), but eventually each egg has a covering of its own. Between very
young ova (e) no larger than the epithelial cell, and the maturer egg (e') every stage can be
traced. The yolk appears very early as a fine granular deposit in the protoplasm of the cell.

In this species the development is nearly direct, there being no zoéal stage, and the egg
contains more than nine times as much yolk as the egg of Alpheus minus, in which the first larva
is a zoéalike form, The materials for the yolk must be derived directly from the blood, and in this
form the germinal epithelium is bathed with the blood current. Where there is an enormous food
yolk blood must be supplied to the developing ova in more than the usual quantity. This is often
accomplished by reéntrant blood sinuses which penetrate all parts of the ovarian stroma, as in
the lobster (Homarus) and in the cephalopods, which are precocious in development and conse-
quently deposit a great store of yolk in the egg. In the latter the follicular epithelium is folded
in a remarkable manner about the egg to increase its nutritive surface.

The germinal vesicle (Fig. 11, G. V.) is filled with coarse chromatin grains, and in the early
phases grows relatively faster than the rest of theegg. In the egg, (e,' to the left) which is z3,5 inch
in diameter, the diameter of the germinal vesicle is one-half that of the entireegg. The chromatin
grains increase in size until there are formed, as in an egg like the last, six or more large masses
of chromatin, or nucleoli. The older eggs are spherical; their food yolk is often vacuolated, as in
later stages, and they are invested by a single membrane, the chorion, which is a chitenous secre-
tion of the follicular cells.

In the ripe ovary of this Alpheus the mature eggs fill the ovarian sac, except at the lower
portion next the middle line, where, as already stated, the young ova first make their appearance.
These mature eggs are closely crowded and irregular in shape, and their bulk greatly distends the
body of the prawn. The chorion is now fully formed and closely invests the vitellus. The yolk
is in the form of spherules, usually fased and always vacuolated in preparations which have been
subjected to alcohol and turpentine. In the ripe egg the nucleus was not seen, but it is quite
probable that careful sectioning would show that it lay at the surface, as is the case with the ripe
ovarian egg of the lobster, which is often left in the ovary, after the bulk of the eggs are laid.
We thus conclude that the extrusion of polar cells may be internal, that is, may take place within
the ovary, as is sometimes, if not always, the case with Homarus.

(b) The Lobster (Homarus americanus).—The ovaries of the lobster consist of two lobes or rods
of tissue, united by a short transverse bar. When filled with eggs their color is a dark olive
green, except in young females, where the color of the immature ovary is variable. Each lobe is
composed of an outer wall, which is a felt of muscle and connective tissue fibers with very small
nuclei, and of a loose framework of germinal epithelium, which penetrates all parts of the lobe.
The latter is a syneytium and consists of a matrix in which great numbers of small nuclei are
embedded. These nuclei, with surrounding protoplasm, give rise (1) to ova and (2) to cells of the
egg follicle. ‘

The growth of the ovarian egg from the epithelial nucleus is illustrated in Pl. xxv, Figs. 3, 6.
Vig. 6 is from a section through the posterior end of an ovarian lobe of a lobster obtained from the
Baltimore markets in January. Fig. 3 shows the central portion of this section greatly enlarged
The diameter of the entire section is about twice that of the part represented in Fig. 6, and the
oldest eggs lie at the periphery. The germogens, the centers of dispersion of new eggs, lie nearly
in the long axis of the lobe. We can therefore trace in a single good section at this stage the de-
velopment of the egg through every stage, from the indifferent nuclei of the ovarian stroma to the
large peripheral ova. The ovary is supplied with blood by means of sinuses which penetrate to
all its parts (BI. 8.). The sinuses are definite reéntrant channels with thin membranous walls.

The ovarian tissue (Ct. 8.) consists of a fibrous matrix in which numerous oval granular nuclei
are embedded. The process of the conversion of the epithelial cells into eggs is shown in Fig. 3.
The epithelial nucleus (O, 0”) swells out, becomes spherical, and its chromatin has the charac-

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 395.

teristic granular appearance of the germinal vesicle of the young egg. The first trace of the yolk
(O%, O*, O°) appears in the outer granular layer which surrounds the germinal vesicle. This layer
represents primarily the cell protoplasm, in which the yolk is formed. The cell takes on a definite
shape and is very early invested with a follicular coat (I. C.). In an egg a little older (O*) the
nucleolus has appeared, and in still older eggs (Fig. 6, O, O') a delicate chorion (Ch.) can be
seen. This is secreted by the cells of the follicular envelope (I. C.). The growing eggs pass out
from the central to the peripheral parts of the lobe iv the sheets of stroma between the blood
sinuses. Distinct yolk spherules are very early seen (O°) and are of uniform size, but in maturer
eggs (Fig. 6, O, O') the germinal vesicle is sometimes surrounded by a central layer of small
spherules and a peripheral layer of larger ones. The germinal vesicle is centrally situated and
always contains a single excentric nucleolus, besides stellate masses in the chromatin reticulum.*

(c) The Spiny Lobster (Palinurus).—In the spiny or rock lobster from the Bahamas the ova
originate exactly as in Homarus, and the structure of the ovary is essentially the same. There
are several nucleoli, as in Alpheus. The ovary is not nearly so richly supplied with blood sinuses
as in the cases just considered. This is perhaps correlated with the fact that the amount of yolk

and the subjoined notes are largely extracted from a preliminary notice on ‘The Reproductive Organs and Early
Stages of Development of the American Lobster.” (23.)

The structure of the mature ovary is somewhat peculiar. The free, unextruded eggs fill the lamen of the
ovarian lobes. The lobe or tube itself consists of the proper ovarian tissue and the outer muscular wall, which is
very thick. The stroma is characterized by the presence of gland-like structures, blood sinuses, and immatnre ova.
The glands are in close relation with the growing eggs. They are plaited or folded structures, and consist of a single
layer of columnar cells, the boundaries of which are indistinct. The lumen of the fold usually contains a granular
residue, but often yolk and degenerating nuclei. It-seems possible that these structures are comparable to yolk
glands, and that their function is to supply the growing ova at this stage with a part of their massive food yolk,
Three days after the extrusion of the eggs the glandular ceca have much thicker walls; the rapidly dividing cells
are suialler, and their nuclei lie at various levels. In another ovary of about the same age the glands are relatively
very large. The columnar cells are greatly elongated, their nuclei lie at the deeper or outer ends of the cells, and
the lumen of the gland is often completely obscured. The gland forms a kind of egg tube, abutting upon and partly
inclosing the growing egg. The columnar cells stop short at the sides of the egg, so that the glandular cecum resem-
bles a narrow bag with an egg pushed into its mouth. The glandular cells are directly continuous with those of the
follicle. The axial portion of this ovarian lobe is composed of hollow spaces, blood sinuses, and loose stroma, int
which very young eggs occur. Degenerating cells occur not only in the stroma, but probably in the developing ova
also. In Peripatus Nove Zealandiaw the yolk is described by Lilian Sheldon as arising not only from the egg proto-
plasm, but also from the follicle cells (57),

When ten to fifteen days have clapsed after egg-laying (eggs in egg-nauplius stage), the gland-like bodies
have almost wholly disappeared. The walls of the cxca are shrunken and crumpled, and the latter have been
crowded to the extreme periphery of the ovary. The ovary now contains a solid core of immature eggs, stroma, and
bloodvessels. This is continuous with radial sheets of similar tissue which extend from the center toward the pe-
riphery. The outer and more mature masses of ova are thus divided into more or less continuous, longitudinal bands.

At a still later period (eggs with eye pigment, four to five weeks’ old) the glands are present merely as
shriveled remnants. Later still (lobster taken August 21; egg embryos in a late stage’) there is no trace of gland-like
structures. In the ovary of a lobster (taken June 30), with eggs about to hatch, the condition is similar to the last.
It is now abont eleven months since the eggs were laid, yet the diameter of the largest ovarian ova is only about one-
half that of the mature eggs. ‘The ovarian wall is thinner than in previous stages, and in the axis of the lobe there
are still sheets of very small, immature ova.

It seems that the bodies which bave been described as probable yolk glands are present in the peripheral
parts of the ovaries only during the limited period of from two to three weeks after the eggs are laid, and when the
org ins are recovering from the changes which follow this event. Their structure is quite unlike that of bloodvessels
or sinuses with which they are intricately associated, and their relation to the growing eggs seems to imply that
they have some function to perform in the nourishment of the peripheral ova. Their short existence, on the other
hand, might lead us to suspect that they were more or less rudimentary structures, or that they were concerned with
the secretion of the gluey substance with which the eggs are coated at the time they are laid. Their true function,
however, remains to be determined.

Ovaries which I have examined, taken in summer (July) from lobsters ( ‘‘ paper shells”) which have receutly
moulted and which do not carry eggs, present very thin walls, and the largest ovum measures in diameter about one-
half that of the mature egg. These lobsters have probably hatched a brood the present season and have afterwards
moulted. (Compare the ovary of the lobster taken June 30 above.)

Some allowance is to be made for individual difference, but the slow growth of the ovarian ege, which we
have traced from the snmmer when eggs were laid to the following summer when these eggs were hatched, is very
noteworthy, and shows conclusively that the lobster is not an annual breeder.

396 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

in each egg is very small, although the number of eggs produced by this animal is enormous. At
Nassau, Palinurus begins to spawn in June.

(da) Comparison.—Ishikawa describes very fully the ovaries and ovigenesis of the prawn At-
yephyra compressa and concludes that the ovum “originates from the infer lining of the ovary and
is at the beginning a cell with a nucleus and one, two, or rarely three nucleoli” The mature egg,
according to this observer, has two membranes, one of which is due to the “hardening of the
peripheral protoplasm of the egg,” while the other (secondary egg-membrane) is secreted by the
epithelial cells of the oviduct and added at the time the eggs are laid.

There seems to be an error here in regard to the origin of the chorion. In the Decapod Crus-
tacea it is the rule that the chorion it secreted gradually during the growth of the egg by the cells
of the egg follicle. The large glandular cells found in the oviduets of Atyephyra possibly secrete
the viscid fluid by which the eggs are attached to the swimmerets, yet this point needs comfir-
mation.

The chorion was found in the ovarian egg of Pagurus by Mayer (39), who says:

Das Eierstocksei von Pagurus ist in der ersten Zeit seines Bestehens eine echte Zelle mit Protoplasma, Kern und
Kern-Kérperchen. Spiiter findet eine Einlagerung yon Deutoplasma und die Bildung einer Hiille aus Chitin statt.
Endlich wird der Kern unsichtbar; das Ei stellt dann eine Cytode vor.

Das fertige Ei verliisst den Leib des Krebses ohne Kern und mit einer Hiille versehen.

This description answers for Alpheus in all essential points.

The ripe egg of the crayfish (Astacus fluviatilis) is inclosed by a single envelope, the chorion.
According to Ludwig and Waldeyer it is not known whether this is a product of the egg or of the
follicle cells. Huxley (26) merely states that “a structureless vitelline membrane is formed between
the vitellus and the cells which line the ovisac.” The ovisacs burst and the ova pass through the
ovary into the oviduct. When laid, the eggs “are invested by a viscous, transparent substance
which attaches them to the swimmerets of the female and then sets.” Here as in other forms the
chorion is clearly the secretion product of the ovisac. 7

In Cranyon vulgaris Kingsley (31) finds that the late ovarian ova resemble the newly laid
eggs. There is a thin structureless envelope (chorion), but no trace of an inner vitelline membrane.

Ludwig’s general statement that the egg cells of all Arthropods are surrounded by a vitelline
membrane (Dotterhaut), the product of the egg itself, is certainly erroneous. He divides the egg
membranes into primary egg membranes, those which are derived from the protoplasm of the egg
itself or from its follicle cells, and secondary egg membranes, those formed by the wall of the oviduct
or otherwise. Balfour, following Van Beneden, restricts the term vitelline membrane to structures
derived from the protoplasm of the ovum, and chorion to those formed by the cells of the follicle
or oviduct. In the category of secondary structures would fall also those secreted by special
glands, found, according to Ludwig, in Trombidium, Chilopoda, and nearly all Crustacea, and the
winter eggs of Daphnia and Tardigrada, which is due to a moult or direct separation of epithelium
from the body of the mother.

In speaking of the vitelline membrane Van Beneden and Bessels, in their monograph on the
formation of the blastoderm (60), thus define it:

Nous entendons la membrane vitelline dans le sens ou M. Claparéde I’a si nettement définie dans son travail sur
les vers Nématodes: C’est la couche externe du protoplasma de Vuf, qui, ayant acquis une densité plus grande que
la masse sous-jacente, se sépare de celle-ci par un contour net et tranché. Elle est A ’@euf ce que la membrane cellu-
laire est 4 la cellule; elle se forme de la méme manieére.

According to this view the ovum is morphologically a cell, the vitelline membrane is the cell
wall,

The origin and growth of the egg in Amphipods (Gammarus locusta) agrees quite closely with
what takes place in Alpheus and Homarus. According to Van Beneden and Bessels (60) the
young ova are at first protoplasmic cells, the nucleus of which becomes the germinal vesicle. The
ovarian egg is a cell without a membrane, and in the cell protoplasm refringent vesicles are devel-
oped which form the yolk elements. According to these authors the mature ovarian egg consists
of a viscous, finely granular, and contractile liquid, which represents the primitive cell protoplasm
and holds in suspension the germinal vesicle, and, secondly, of nutritive yolk elements (called by
them deutoplasm because of secondary origin), which are also suspended in the protoplasm of the

egg.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 397

In iasects it appears that a chorion is always present in ovarian eggs, while, on the other
hand, arachnids possess a vitelline membrane and the eggshell is secreted in the oviduct.

There is no simple rule to express the appearance of egg membranes in a diversified group
like the Arthropods, and, considering that these structures are purely secondary to the cell and
expensive products however formed, this is what we should expect. Their function is chiefly pro-
tective, and where a chorion is present in the ovary a yolk membrane is not developed, but the
latter is present, as in spiders, when the shell is a later product. Erdl (15) describes three egg-
membranes for the lobster, but it is clear, as Mayer has already shown, that the inner, delicate
membrane which has been described for the decapod egg, is a secretion product of the blastoderm.

Ill. SEGMENTATION OF THE EGG OF ALPHEUS MINUS.

In the small green Alpheus of the southern coast we have a peculiar modification of the usual
process of segmentation, which seems to be anomalous.

The fertile egg is pervaded with a remarkably fine reticulum, which incloses yolk spherules
of minute and uniform size. The nucleus is central, or nearly so,* and consists of an ill-defined
mass of protoplasm, in which a fine chromatin network is suspended. In the next phase (Pl. xxv1,
Fig. 14) the nucleus is elongated and about to divide. Division appears to be direct and irregular.
At a somewhat later stage the phenomena of the most interest occur (Figs. 12,13). Each product
of the first nucleus has developed a swarm of nuclear bodies (S.8.), which seem to arise by fragmen-
tation. These bodies take the form of spherical nuclei in clear masses of protoplasm. The yolk
frequently has a tendency to segment about the nuclear masses, in the same way that it divides
about a single nucleus to form a yolk pyramid. This yolk segmentation seems to be normal, but
it is very irregular. In one case there were two large segments, which nearly divided the egg in
two, besides several smaller ones. Nuclear matter consists either of small particles or of indefi-
nite reticulated masses, resembling the first nucleus (Fig. 14). Clear areas are sometimes found.
with nuclei which appear to be breaking down. About eight nuclear swarms or clusters are present
in the stage shown in Figs. 12,13. The nuclei vary in size from refringent particles to bodies of
ordinary nuclear appearance.

Figs. 25 and 26 represent two sections of one of the clear areas in the same egg from which
Fig. 12 was drawn. This clear field has several degenerating nuclei near its border. The largest
one (S. C.) is included in both sections. A small chromatin mass with indistinct body lies next
it (S. C.?), and other similar bodies occur in different sections. The cell S. C. contains two chro-
matin balls, and in Fig. 26 (the next section but one in the series) this body appears to be dis-
charging through its broken-down wall numerous minute elements (8.) into the clear field. In
Fig. 22 a small protoplasmic area occurs, in which a single nucleus lies. This body is granular
and contains a large chromatin ball. Figs. 5 and 23 are also from the same egg. Here we see
structures similar to the ceil just mentioned. They are surrounded by yolk and consist of a deli-
cate reticulum in which usually one large nucleolus is suspended, besides great numbers of small
chromatin particles.

Various stages of growth are here represented, and it might appear at first sight that we have
a case of endogenous cell formation. I see no reason to suppose that the eggs examined are abnor-
mal, and I conclude that we rather have in this species a remarkable modification of the usual
indirect cell division, attended by an equally remarkable degeneration of nuclear material.

In the last stage obtained (Fig. 29) the whole egg is filled with several hundred very large
elements, which are descended more or less directly from some of the nuclear bodies just consid-
ered, but the intermediate stages have not been traced. This probably corresponds to stage vr of
A. sauleyi, at the period just before invagination, but it is quite unlike anything which I have seen
in other species. The yolk is now irregularly segmented into blocks or balls, but probably not
with reference to these cells.

This case is interesting when we compare it with the degeneration of cells to be deseribed in
another section, and from a cytological point of view it deserves careful study.

“In single sections the nucleus is strictly central, but whether it is so with respect to the entire egg it is not easy
to determine. Minot states that the egg nucleus is always eccentric.—Am. Naturalist, Vol. xxu1, 1889.

398 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

IV.—THE DEVELOPMENT OF THE EMBRYO.

STAGE I.—SEGMENTATION TO FORMATION OF THE BLASTODERM.

These observations relate to Alpheus heterochelis of the Southern States, to a Bahaman form
which hatches as a zoéa but which otherwise resembles this species very closely, and to Alpheus
sauleyi, also the from Bahamas, which has large eggs and a nearly direct development. Except
where it is necessary to mention specific differences, these three species will be treated as one form.

In June two Alphei (A. sauleyi) laid eggs in an aquarium, but the ova were in each case
unfertilized, and for the most part failed to adhere to the swimmerets. One of these eggs, hardened
at an interval of five hours after it was laid, is shown in section on Pl. xxvu, Fig. 17. I regard
the nucleus of this egg as the female pronucleus. It consists of clear protoplasm, which stains
feebly and sends out processes on all sides into the yolk, and of an indefinite chromatin network
suspended in it. The massive yolk is composed of corpuscles of uniform size, excepting at the
periphery where they are much smaller. Numerous small Jacunz occur, representing parts of the
yolk which were soluble in the reagents employed. The chorion, or inner egg-membrane, is
transparent, tough, and very distensible. It frequently splits into thin layers when subjected to
the hardening and embedding process, thus showing the manner in which it is formed in the
egg-follicle. It thus appears that the unfertilized egg of Alpheus is incapable of segmentation.

The first segmentation nucleus has been observed in a few cases. That shown in Fig. 16 is
possibly preparing for division. It possesses a fine reticulum ; itis lenticular in shape, and granular
in appearance, and is surrounded by protoplasm which spreads into the yolk. The once divided
nucleus and the next phase with four cells were not obtained in Alpheus, but the latter was seen
in an allied prawn (Pontonia domestica), and is shown in Fig. 27. One of the three cells present is
in the aster stage of karyokinesis and has a well-marked equatorial plate. The third segmenta-
tion phase is illustrated in Figs. 9, 28,and 30. In the section through the entire egg, three of the
eight cells present are met with, and one of these (x) is shown with greater detail in Fig. 30. A
cell in process of division is represented in Fig. 28. In another egg with eight cells present, two
are undergoing division in different planes. As before, the cells consist of a chromatin network
of various shapes surrounded by a clear protoplasmic body, which sends out processes between the
surrounding yolk spheres. It is important to notice that the products of the segmentation of the
first nucleus pass gradually and uniformly to the surface of the egg. At this stage they have not
reached the surface but are visible through the egg shell. The yolk in these specimens consists of
spberules or angular blocks (Fig. 28, Y. S.), which are largest in the center of the egg, and con-
tain very few vacuoles.

The fourth phase of segmentation is attended by the cleavage of the superficial parts of the
yolk (Fig. 10) around the nuclei, thus giving rise to sixteen blastomeres or partial yolk pyramids.
The division of the yolk proceeds but a short distance below the level of the nuclei, so that all the
yolk-pyramids open by their inner ends into the common yolk mass whieh fills the segmentation
cavity of the egg. The base of the pyramid, which abuts on the surface is polygonal in shape, and
at its middle point some distance below the surface, the nucleus is seen with its investments of
protoplasm. The nucleus is large and granular, and the protoplasm which surrounds it reaches
out on all sides into the yolk. We may look upon the yolk pyramid as a cell in the strict morpho-
logical sense, its protoplasm being concentrated about the nucieus. The blastoderm or primitive
ege envelope arises through the multiplication and consequent reduction in size of these huge
yolk elements. The surface has then the usual appearance of a fine mosaic of hexagonal plates
or cells, the nuclei and surrounding protoplasm of which lie at the surface.

The fifth segmentation phase is shown in Figs. 15 and 51. The septum between the pyramids
extends farther into the yolk, while the nuclei are slightly nearer the surface, and the long axis of
each is parallel with it. This particular egg was taken in a period of “rest,” but in others the
nuclei are in karyokinesis, the division being always radial or in a plane at right angles to a
surface tangent. e

The segmenting egg of Hippa talpoides is shown in Fig. 1 (32-cell stage), and a section of a
later phase in Fig. 4. The egg appears to have undergone a total segmentation when seen
from the surface, but this is not quite so marked as represented in the sketch, The yolk pyramids

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 399

(Fig. 4, Y. P.) agree with those in Alpheus and are probably formed in a similar way. In Pale-
monetes vulgaris the history of segmentation appears to be essentially the same. The nucleus
and base of one of the yolk pyramids of this form is shown in Fig. 24. Here we see that the peri-
nuclear protoplasm has a rayed appearance, being produced in all directions into very delicate
threads which ramify among the yolk spherules. Some of these threads moreover unite with a
thin septum (Sep.) which forms the boundary wall between two adjacent yolk pyramids.

Segmentation proceeds with a regular rhythm up to the fifth stage, but beyond this it soon
becomes irregular. <A blastula is thus formed, consisting of a single layer of cells or blastoderm,
and the inelosed central yolk. All the nuclei reach the surface and take part in forming the
blastoderm, so that all the protoplasm of the egg which is at first central or internal, comes gradually
to assume in the course of segmentation an external position with respect to the food yolk. The
blastodermie cell is the direct descendant of the yolk pyramid. It is improbable that the yolk con-
tains any active protoplasm, excepting that which radiates from the nuclei, and which is descended
from the perinuclear protoplasm of the first segmentation nucleus.

STAGE IJ.—THE BLASTODERM AND INVAGINATION.

The prawn when discovered with eggs in the fifth stage of segmentation (Fig. 15) was kept

in an aquarium, and the ova were preserved at intervals of several hours. Thus it has been
possible to follow the changes which take place between segmentation and invagination with
considerable detail.
, The egg represented in Fig. 47 is about 15 hours older than last described (Fig. 15). Cell
division, which is now irregular, has become accelerated over a part of the egg so that a germinal
area or disk (G. D.) representing the future embryo is formed. The side of the egg shown in
Fig. 47 corresponds to that occupied by the germinal disk. In reverse view there are much fewer
nuclei. The egg has thus lost its radial symmetry and become two sided. Invagination soon
follows this stage’ at a certain point in the germinal area (G. D.). The superficial cells of the
blastoderm (lig. 48) are about one-third their former size, but they still have the characteristics
of the yolk pyramids. The cell is polygonal in surface views; the nucleus is surrounded by yolk
and the cleavage planes between adjacent cells (Fig. 38, Sep.) are still present.

This stage is characterized by the passage of large numbers of cells from the surface to the
central parts of the egg just before the invagination takes place. This process is well illustrated
by a series of consecutive sections (Figs. 38-44) taken from the same egg. In all these sections
the cleavage of the yolk can still be seen. Many of the blastoderm cells (Fig. 39, a.) are in different
phases of division, the dividing plane being always perpendicular to a surface tangent. It is
probable, therefore, that the nuclei with their perinuclear protoplasm, leave the yolk pyramid
and pass by amceboid movement into the interior. It is, therefore, evident that while morpholog-
ically the yolk pyramid is a cell, the elements which pass into the egg have also the value of
cells in a physiological sense. Six nuclei are met with in Fig. 38, one of which has wandered
some distance from the surface. In the next (Fig. 39) two cells (a. a!.) are in the aster phase
of division; one (a?) has passed just below the surface, and another (a*) is near the center of the
egg. These cells (a, a’, a*,) are sectioned again in the following figure (Fig. 40). Various phases
of the process of migration* are seen in other members of this series. In an enlarged portion
of a similar section (Fig. 37) several cells are met with, some at the surface just beneath the
shell, and others at some distance below it. The protoplasm about the nucleus has no defi-
nite bounds, and is often filled with fine particles of food yolk. It is thus evident that these cells
feed essentially like amcebx, by taking the food directly into the protoplasm of the cell.

The critical stage at which cells begin to pass from the superficial to the central parts of the
yolk was obtained in an egg just thirteen hours older than the fifth segmentation phase, shown in
Fig. 15. There are about a dozen yolk cells in this egg, and one of these is in karyokinesis. The
remainder lie very near the surface, but for the most part are separated from it by a thin layer of
yolk spheres. It is thus clear that the migration of cells to the central parts of the egg begins

* In the lobster the primary yolk cells arise by delamination, and as suggested in Section V, this is possibly true
of Alpheus,

400 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

before all the protoplasm, that is, the nuclei and perinuclear protoplasm of the yolk pyramids,
has reached the surface. In the slightly older phase, shown in Pl]. xxx, Fig. 46, all the proto-
plasm which does not pass inward is strietly superficial. The yolk has the same appearance as
in previous stages, and, as already noticed, the cleavage planes (Sep.) between yolk pyramids are
still met with. Very soon, however, the central portion of the yolk segments into balls or angular
blocks (Fig. 46, Y. B.), apparently with reference to these wandering cells. A section through the
germinal disk of an egg seven and one-half hours older than that shown in Fig. 47 is given in Fig.
57. The cells in the area of the germinal disk are quite closely crowded, and the superficial seg-
mentation of the yolk is still apparent. We now have a primitive epiblast, or external layer of
cells, and a primitive hypoblast, composed of yolk cells which have migrated from the blastoderm.

The invagination stage immediately follows that last described (Pl. xxx1). A slight depres-
ion occurs at a point on one side of the germinal disk, where the cells are multiplying most
rapidly, and numerous cells pass downward into the yolk. The invagination is nearly solid, and
the segmentation cavity is still filled with the great mass of yolk and with primitive hypoblast.
In the erayfish (Astacus fluviatilis) the invaginate cavity becomes a closed chamber within the
yolk (54), and this is eventually converted into the midgut, but in most decapods the pit is very
small and the mesenteron is formed independently at a later period. A line drawn through the
pit and the middle of the germinal disk marks the long axis of the embryo, and the point of
ingrowth is at the posterior end.

The structure of the embryo is illustrated by a series of transverse sections (Pl. xxx1). The
cells in the center of the egg represent the primitive hypoblast or yolk cells. The nuclei are
large and granular, and sometimes occupy the center of a yolk ball. In Fig. 49 the posterior edge
of the embryo is sectioned, and the three following sections (Figs. 50-53) pass through the region
corresponding to the invaginate area (Ig). Fig. 52 represents the entire Section, of which Fig.
5 is a part. ‘The pyramidal cells, which form the floor of the depression, contain at their
peripheral ends no unabsorbed yolk, but at the deeper ends of the cell, below the level of the
nucleus, the cell boundaries are lost, and the protoplasm of the cell blends off into the yolk and
ingulfs its finely divided particles (Fig. 50). Numerous cells (Figs. 52-54, b, b'*) have already
wandered from the point of invagination into the egg and a considerable distance forward under
- the germinal disk (Fig. 54, G. D.). These cells aré more or less intimately united by pseudopodal
extensions of the protoplasm. A coarse reticulum is thus formed, the meshes of which are filled
with yolk. In front of the invaginate cells, the germinal disk (Fig. 55, G. D.) is still one cell
thick. At the close of the invagination stage the primitive hypoblast has received a consid-
erable acesssion of wandering cells. This stage is usually described as the “egg-gastrula,”
in accordance with the theory that it represents an ancestral condition, and that the cavity
formed at the surface is the remnant of the primitive digestive tract. The discovery of delami-
nation, the actual separation of the inner ends of the cells of the blastula by karyokinesis before
any invagination occurs, as I have described in the lobster, and the occurrence of this or of mul-
tipolar emigration in Alpheus, together with the fact that in the typical decapod the invagination
has no direct relation to the digestive tract or to to the mouth and anus, point to the view already
expressed in a preliminary paper upon the lobster (23), that the. invagination stage has no refer-
ence to an ancestral invaginate gastrula. It seems to me more probable that the egg with primary
yolk cells corresponds to the celenterate planula stage, and that these yolk cells, which originate
from the blastula and which partially or entirely degenerate, represent the remains of a primitive
hypoblast. According to this view the invagination is a secondary process, which became so
indelibly impressed upon the ancestors of the Decapods that it has remained in the ontogeny of
present forms. The conditions which are found in the crayfish can not be regarded as in any
sense general or typical.

SraGE III.—Opric DISKS AND VENTRAL PLATE FORMED.

This stage (Fig. 58) is characterized by a thickening of epiblast which gives rise to the tho-
raci¢-abdominal or ventral plate in front of and around the point of ingrowth, by the simultaneous
spreading of invaginate cells below the surface, aud by the appearance of the optic disks (O. D.),

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 401

two patches of ectoblast on either side of the middle line in front of the ventral plate. When
the living egg is examined by reflected light these structures appear as misty white patches sep-
arate from each other- (See Fig. 2.)

The principal cell mass is the thoracic-abdominal plate (Fig. 58, Ab. P.), from which the
thoracic-abdominal process is developed. The position of the pit (Ig.) is faintly marked by the
arrangement of the cells at that point. The optic disks are due to the rapid multiplication of epi-
blastic cells around definite centers. Each is joined to the ventral plate by alateral band or cord
of cells (L. Cd.), on which the appendages are subsequently budded off. A transverse cord (T.
Cd.) soon bridges over the space between the optic disks, thus inclosing a triangular area, which
corresponds largely to the sternal region of the adult. The extension of the invaginate cells below
the surface is only partially indicated by the shaded nuelei. They advance forward and backward
from the point of ingrowth, but principally upward, that is, toward the center of the egg, along
the lines joining the optie disks tu the ventral plate (Figs. 59, 60). The embryo covers nearly
one hemisphere of the egg. It is V-shaped, but the angle between the arms of the V varies much
in different eggs. There is a marked contraction of the embryo which takes place immediately
after this phase, that is, the area of the surface occupied by the embryo becomes appreciably
smaller. A similar contraction of the embryo has been observed in Astacus (54) and Crangon (31).
With the extension of the epidermis there has been a corresponding activity among the wandering
cells. Their relations are well shown by sections through the entire egg (Figs. 56, 59, 60), in which
we can still distinguish the primary yolk cells (P. Y. C.) from the cells derived from the invagi-
nation (S. Y. C.). The cells of the first have large, granular nuclei and send out processes into
the yolk. The others are smaller and are probably multiplying more rapidly. It soon becomes
impossible to find any distinction between these wandering cells. The yolk is irregularly seg-
mented into balls (Figs. 60, 63, Y. B.), inside of which the migrating cells are usually found. The
epiblastic cells of the surface, which are the direct descendants of the yolk pyramids, have definite
boundaries, but some of the cells of the ventral plate (PI. rx, Figs. 61, 63) tend to form a syn-
eytium, as already seen, while the wandering cells are independent, free-moving elements.

The lateral section (Fig. 56) passes through the outer edge of the ventral plate, and the
next toward the middle line (Fig. 60) encounters a sheet of wandering cells. “ We see at a glance
that the migrating cells pervade the greater part of the egg, and that they pass out in all direc-
tions from the region of the ventral plate (Ab. P.). Fig. 59 represents a median longitudinal
section through the embryo and entire egg, and Fig. 63 a part of a section highly magnified through
the ventral plate and region of ingrowth. The cells immediately below the surface (S. Y. C.)
are characterized by large and very granular nuclei, which stain with much less intensity than the
superficial epiblast. This shows that they are multiplying rapidly, and the finely divided yolk in
their neighborhood shows also that the cell protoplasm is rapidly absorbing food. A series of trans-
verse sections of this embryo is given in Pl. xxx, The plane of section in Fig. 61 is oblique and
passes in a posterior direction. In Fig. 62 the lateral cords (L. Cd.) are crossed and numerous
wandering cells are encountered, while anterior to this (Figs. 68, 69) the optic disks are cut. The
optic disks (Figs. 64-67) consist of a single layer of epiblast. Their cells are flat and polygonal,
cell boundaries are distinet, and the long axis of the oval nucleus is parallel with the surface.
When the cell divides this position is reversed, the plane of division being perpendicular to a
tangent at the surface. From the optic disk the eye and its ganglia are developed.

STAGE LV.—THICKENING OF THE OPTIC DISKS AND RUDIMENTS OF THE APPENDAGES.

An embryo a few hours older than the last deseribed is shown in Fig. 72. On the thickened
cords of cells (L. Od.) uniting the optic disks to the ventral plate the traces of two pairs of append-
ages can be made out—the first pair of antennze A (I.), and, close to the ventral plate, the mandibles
(Md.). Some of the central cells (C. M.) of the optic disk have large, granular nuclei. These
mark the area of most active cell division, and form an ingrowth or thickening, which is the rudi-
ment of the optic ganglion.

Glancing at a series of longitudinal sections through this egg (Figs. 70-71, 73-75), we notice

S. Mis. 9426

402 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

several important changes since the last stage. The ventral plate is more extensive and the
wandering cells are more numerous. The primary and secondary wandering cells can no longer be
distinguished, but all the cells within the yolk are similar in character. They have large, granu-
lar nuclei, and multiply by ordinary karyokinesis (Fig. 75, Y. C*.). Some pass forward underneath
the embryo (Fig. 74, Y. C.) and to other parts of the egg. In Fig.-71 two yolk elements are
found near the lateral cord, and in Fig. 70 one is seen just under the optic disk. In Fig. 75
the section is median and corresponds closely with the similar longitudinal section of the last
stage (Fig. 59.).. The transverse cord (T. Cd.) is seen to consist of a single layer of flat epiblastic
cells.

The structure of the ventral] plate is shown in detail in Fig. 85, which is a section just in
front of the point of invagination. This illustrates the character of the syncytium beneath the
surface of the plate and the fine degree of fragmentation which the yolk suffers in the presence
of the cell protoplasm. At the surface, the cell walls are quite distinct, as already seen, but as
soon as the cells pass below it, the protoplasm extends itself in pseudopodia-like processes and
incloses particles of yolk. Under these favorable conditions of nourishment these elements, which
must be regarded as the mother cells of the mesoderm and the endoderm, multiply rapidly and
spread to all parts of the egg. If this section is compared with that of the invaginate stage (Fig.
54), and with a similar section of Stage m1 (Fig. 61), it is easy to understand the relations of the
ventral plate to the wandering cells, and the way in which the thickening of the plate is brought
about. At the second stage comparatively few cells take part in the invagination, and the most
of these pass directly into the yolk. But, almost simultaneously with this migration of cells there
occurs a migration of cells from the surface of the ventral plate. Thus this becomes thickened
and cells continue to be supplied to the yolk. This thickening of the plate is possibly due to cell
division in both planes; thatis, to delamination and emigration. (Compare cells EC, EC'S, Fig. 85.)

The process by which the optic disk becomes thickened at this stage is quite. similar, although
there is no true invagination concerned in it. This is shown by a series of connective sections
(Figs. 76-83) passing through the entire disk. The anterior rim of the disk is cut in Fig. 76, and in
Fig. 83 the rudiment of the first antenna. This thickening is mainly the result of the migration of
epiblastic cells from the surface. After leaving the surface, the cell wall usually becomes indefi-
nite. The relations of the optic disks to the entire egg are seen in Fig. 84. The central yolk is
segmented as shown in Fig. 74, and a yolk cell usually lies within the segment.

STAGE V.—RUDIMENTS OF THREE PAIRS OF APPENDAGES—CELL DEGENERATION.

The embryo represented in Fig. 93 is, approximately, three days old (temperature at Nassau
78-80° F.). It occupies nearly one entire hemisphere of the egg, the opposite side of which is
covered with flat epithelial cells like those seen at the periphery of the figure. The shape of the
embryo proper is nearly that of an equilateral triangle, one angle of which corresponds to the
ventral plate, and the other two to the optic disks. A line drawn through the first of these angles
and the middle of the opposite side would therefore correspond with the longitudinal median
axis of the embryo.

The rudiments of the second pair of antennz, A (II), have now appeared, and we therefore
have present at this stage buds of three pairs of appendages, namely, the first and second pairs of
antenne and the mandibles. All are developed nearly simultaneously, but the second pair of
antennze seem to lag a little behind the rest. In respect to the order of appearance of these
appendages, allied species of Crustacea differ slightly. The central parts of the ventral plate
(Ab. P.) and optic disks (C. M.) are areas of rapid cell division, and are characterized by the presence
of large granular puclei and by the irregular arrangement of the cells. In all other parts of the egg
the superficial cells form a uniform stratum one cell deep. This irregularity is due to the gradual
migration from the surface of individual cells in these three places. The first pair of antennz
are closely associated with the optic disks, and the mandibles abut against the ventral plate on
either side of the middle line. The appendages start on the lateral cords from definite centers of
cell division, and the cells tend to assume a radial and concentric arrangement around each center.

The space between the optic disks is now completely bridged over by a sheet of closely

a en fare

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 403

crowded cells (T. Cd.), and the backward extension of this, and the approximation of the lateral
cords has quite closed over the central or sternal region of this part of the embryo (St. A.). Cell
outlines are very distinct at the surface in preparations, and they are sometimes well defined in cells
which have passed from the surface to parts below it, in both the region of the optic disk and
that of the ventral plate (Fig. 80, Ec.), but elements closely associated with yolk are usually am«-
boid. The nucleus of the epiblastic or epithelial cell on the confines of the embryo, or on the extra-
embryonic surface of the egg, has the shape of a flattened, round, or oval disk. Epiblastic nuclei
in the appendages and other parts of the embryo, where there is rapid cell division, are angular
in consequence of crowding, and deep-lying nuclei are generally spherical.

The arrangement of the embryonic cells of the superficial epiblast in beautiful curves and rings
around definite centers—orthogonic systems of curves—is not nearly so pronounced as in the embryo
crayfish (Astacus fluviatilis), according to the delineations of Reichenbach and Winter. Reichen-
bach states that in the crayfish the superficial embryonic cells multiply about a given center, like
that of the “head fold” (optic disk), or “ thoracic-abdominal rudiment,” according to definite
laws. This was discovered by Sachs in the growing tips of plants. According to Sachs, Reich-
enbach, and others, the cell nuclei always divide in one of two opposite planes; that is, they either
separate along a radius drawn from a given center, thus giving rise to radial strings of cells,
or in a plane at right angles to this, producing new strings. Thus there is developed about the
initial cell a series of concentric circles and radiating lines of cells. The positions of the equa-
torial plates of dividing nuclei, which some eggs of Alpheus show in abundance, do not indicate
the prevalence of such a law in the earlier stages. The early embryo of Alpheus is much less
diffuse than in the crayfish, aud the different cell groups soon impinge on each other, and their
relations are disturbed.

Several transitional stages between the last two embryos figured (Figs. 72 and 93) will now be
examined. The first is represented by three longitudinal sections (PI. xxxv1, Figs. 88-90), and is
about seventy hours old. It is from the same prawn as the segmented egg shown in P1. xxvit, Fig.
15, These sections give some interesting facts with reference to the role of the wandering cells.
The first (Fig. 88), which is nearly median, cuts the ventral plate and below it the cells which are
migrating from it into the yolk. A continuous layer of cells extends anteriorly to the transverse
cord (T. Cd.). In this region a wandering, mesoblastic cell (Y. C.) is nearly in contact with the
superficial epiblast. The next section touches the outer edge of the ventral plate (Fig. 89),
which is marked by large granular nuclei, and crosses the lateral cord and rudiments of the ap-
pendages (A. I, A. II, Md.). The folds of the latter arise through the ingrowth of superficial cells.
Here another cell (Y. C.') is close to the outer surface of embryo; another (Y. C.’) is in a distant
part of the egg and is in the aster stage of karyokinesis; others still (Y. C.°) have wandered in a
diametrically opposite direction. In Fig. 90 we see still more of these wandering cells, in this
instance, chiefly above the embryo.

In the middle of the optic disk some of the large granular cells visible from the surface (Fig.
93, C.M.), are met with, and one of them (Fig. 90, Ec. dotted line extended) has just passed below it.

Figs. 86 and 87 are parts of longitudinal sections of an embryo six hours older than the last.
The first exposes the optic disk (O. D.) and gives evidence of the further increase of the latter by
the emigration of cells from the surface, and it is quite probable that some of the wandering, meso-
blastic cells (Y. C.) have already attached themselves to it. (Compare Fig. 90.) In the next (Fig.
87) the inner edge of the optic disk (O. D.) and the outer border of the ventral plate (Ab. P.)
are involved. Here the epiblast consists for the most part of a single layer of cells. Two large
wandering elements (Y. ©.') are in contact with the surface cells of the embryo in the neighbor-
hood of the appendages.

Fig. 91 is from an embryo twelve hours older than the last. The plane of section passes
obliquely through the optic disk, cutting the anterior half of one (to the left) and the posterior
part of the other. A study of this section and of the series to which it belongs, shows us beyond
a doubt what is the fate of large numbers of wandering cells, present at this time. As has been
already shown by preceding figures (see Figs. 73, 88, and others), the cell mass constituting the
thoracic-ubdominal plate is now the principal source of the wandering yolk elements, and, as has
been also shown, they migrate into all parts of the egg, multiply by karyokinesis, and settle

404 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

upon the optic disks, the bases of the appendages, and other parts of the embryo. They also
pass to the extra-embryonic surface of the egg. In Fig. 91 one of these wandering cells (Y. C.)
is approaching the surface, while another (Y. C.') nearly touches it; and in Pl. xxix, Fig. 34,
which represents a portion of a section from a later series (Fig. 106) greatly enlarged, we find
two yolk elements (Y. C.) quite at the surface. They are triangular in outline, one of the flat-
tened sides being applied to the surface of the egg. Histologically their nuclei are more gran-
ular and stain with less intensity than the nucleus of the ordinary epiblastie cell (Ep.), which
appears spindle-shaped in vertical section. But between a cell like that seen in Fig. 91 (Y. C."),
where the long axis of the nucleus is at right angles to the surface, or cells like those shown in
Fig. 34, where the nucleus is flattened against it and the ordinary epiblastic ell, a variety of tran-
sitional phases can be found. This is most clearly illustrated in the next stage.

The egg already described (Fig. 93) shows some important changes. The structure of the optic
disks and ventral plate is readily seen in the transverse (Figs. 92, 94, 95) and lateral longitu-
dinal sections (Figs. 96,97). The optic disk, which in stage 111 consisted of a single stratum of cells,
(Fig. 69), is now a thick cell-mass two-thirds the size of the ventral plate. In it we still distin-
guish a small area of cells with large granular nuclei (Fig. 93, C. M.), which, as we see in Figs. 96, 97,
©. M., O. D., is clearly differentiated. It occupies a position just without (or external with respect
to the longitudinal median axis) the center of the disk. The nuclei of surrounding cells are not
more than half their size. These large cells do not all lie at the surface, but form a solid mass
extending into the yolk. The evidence of karyokinetic figures shows that these cells are dividing,
and usually in planes perpendicular to the surface. This results in the crowding of the cells, and
also in their migration from the surface to parts below it.

In Fig. 90 there is a cell (ec.) whose nucleus has sunk below the level of the surrounding cells,
but the cell protoplasm still reaches up to the surface. Such cases render one cautious in pro-
nouncing positively upon the emigration of cells, but sections like that given in Fig. 94, and the
fact that cell divisions seem to be for the most part in one plane, convince me that the thickening
is partly, if not largely, due to this cause. In Fig. 95, a large cell, the polar star of which is just
below the surface, is delaminating. Cases of this kind were rarely noticed, but were observed at
a later stage (Pl. xxx1x, Fig. 102, ec.). That wandering cells attach themselves to the optic disk,
there is little doubt. They can be traced in all stages of progress from the region of the ventral
plate to the neighborhood of the disk (Fig. 90, Y. C.) until they finally come in contact with it.

The thickening of the optic disk described in Stage 111 (Pl. XX x1II, Fig. 69), is therefore effected:
(1) partly, perhaps largely, by emigration of cells from the surface; (2) partly by delamination ;
(3) by the accession of wandering cells; (4) by the indirect cell division of the elements constitut-
ing the deeper part of the disk.

Chromatin grains make their appearance somewhat abruptly at this stage (Fig. 96, S.!*.) and

they serve to explain in some degree the peculiar granular nature of nuclei in earlier stages. They ©

originate by the degeneration of cells in the ventral plate and in other parts of the embryo, and
probably correspond to what Reichenbach has called in the crayfish ‘‘ secondary mesoderm cells.”
Their history has been fully traced and will be discussed in Section V1.

The structure of the ventral plate (Fig. 92) resembles that of an earlier stage (Fig. 85) with
the difference that the nuclei are considerably larger and contain from one to several large spore-
like masses of chromatin. This cell mass has not increased in bulk at a rate corresponding with
the growth of other parts, since elements are being continually subtracted from it and added to
the yolk. This loss on the part of the ventral plate is made good not only by cell divisions,
but also by continued emigration from the surface (Fig. 98, Ab.).

An embryo six hours older than the last is represented by three longitudinal sections (Figs.
98-100). The optic disks resemble in size and general shape the three pairs of rudimentary limbs.
The abdominal fold is not yet formed and the labrum is undeveloped. The stomodzeum (Fig. 98,
Std.) is just making its appearance as a slight invagination of epiblast on the middle line between
the first pair of antenne. The number of chromatin balls (S) and degenerating cells (S. C.) has
greatly increased. We see them in all parts of the embryo. Sporelike nucleoli are seen in cells
of the epiblast and are confined to no part of the embryo, but they are most characteristic of the
ventral plate and optic disks. BF i)

<
Pb,

.

wee TL Pe ee ae ae eee ne

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 405

In Fig. 98 several independent chromatin balls (S) are seen in the yolk, and the granular
cells of the ventral plate are very marked. <A large nucleus of one of the cells (ec.), which contains
several sporelike bodies, is very irregular in shape, owing to the pressure to which it is subjected,
and it has evidently been crowded down from a level nearer the surface. The cell protoplasm,
however, shows that it still belongs to the surface tier of cells. This is also true of the small len-
ticular nucleus next it on its anterior side. Just anterior to this cell is another (Be.') which is in
the act of dividing in the usual way. It seems probable that had this division been effected one
or more of the adjacent cells must have been crowded quite below the surface. It is difficult,
however, to always determine whether cells whose nuclei are a considerable distance below the
surface do not send up stands of protoplasm to meet it. We find in the ventral plate, inde-
pendent cells multiplying by karyokinesis, and, as evidences of delamination in this region are rare
or altogether wanting, we are convinced that, as in the ease of the optic disks, this thickening is
largely due to the migration of cells from the surface.

There is at this stage a fairly well-defined sheet of cells (Figs. 99, 100, Mes.) extending forward
from the ventral plate on either side. The nuclei are oval or elongated, and their long axes are
parallel with the surface, that is, at right angles to the major axes of the superficial epiblast cells.
This layer of cells is most marked at the bases of the appendages (Fig. 100, Mes.) and extends
from the optic disk on either side to the ventral plate. The question of the origin of these cells
is not difficult. They are wandering cells which have settled down on these parts of the embryo.
They form a part of the future mesoblastic tissues ; exactly what part they play will be discussed
later on. They multiply by indirect division and extend into the folds of the appendages, while
some, on the other hand, degenerate.

STAGE VI.—THE EGG-NAUPLIUS.

The fully developed égg-nauplius is represented in Fig. 111, but before this condition is reached
there are several intermediate stages to be considered. A series of longitudinal sections (PI.
XxxI1X, Figs. 101-105) illustrates the structure of an embryo twelve and a half hours older than
the one last described. The thoracic-abdominal fold (Fig. 104, Ab.) can now be recognized, and
the stomodeum (Fig, 105, Std.) has the form of a straight, narrow tube, between the buds of the
first and second pairs of antenne. The space between these two structures is filled with yolk
fragments, among which are scattered, numerous chromatin particles (S) and cells derived from
the thoracic-abdominal fold. The epiblast of the sternal region (Fig. 105, 98, St. A.) is no longer
asimple layer, but is slightly thickened. This thickening seems to be partly due to rapid cell
division in one plane. The cell nuclei are elongated or wedge-shaped and stand perpendicular to
the surface. As will be.seen later it is also due to the accession of wandering, mesoblastic cells.

The stomodeum is a relatively long straight tube with very slight lumen, and is surrounded
with chromatin grains and seattered cells. It is formed at a considerable distance in front of the
point of invagination, and one to two days earlier than the proctodieum.

The thoracic-abdominal fold seems to arise by the sinking down of the epiblast along a defi-
nite line. There is thus formed a narrow transverse pocket (Fig. 106, Ab. C.), which is quite deep
and perpendicular with the surface. Numerous cells continue to pass from the thoracic-abdom-
inal fold to various parts of the embryo, and to join the sheets of cells (Fig. 103, Mes.) already
mentioned. In Fig. 103 the four segments of the embryo are well shown. This section crosses
the optic dise (O. G.), the buds of the three appendages, and the edge of the thoracic-abdominal
fold. The sheet of mesoblastic cells (Mes.) is most marked opposite the folds of the appendages.

The optic disks are now large masses of cells united by a transverse cord which is thickened
slightly on the middle line. In Fig. 102, three cells are met in karyokinesis, one in the abdominal
area and two side by side in the optic disks. The former exemplifies the common method of cell
division, while the latter is a good example of the less common delamination. As has been already
seen, karyokinetic figures of dividing cells are commonly met with in Alpheus at all stages, except-
ing the species Alpheus minor, where the division is at first probably direct. I have seen nuclear
figures at the yolk segmentation stage of Crangon, also in Hippa, Pontonia and Homarus, and Rei-
chenbach found them in abundance in Astacus. Indirect cell division is undoubtedly the rule in

406 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

the developing eggs of the Crustacea and probably of all the Metazoa. Since we often study only
the rapidly achieved result, the phases of nuclear division may be easily missed.

Fig. 106 is a median longitudinal section of an embryo preserved a few hours later than
the last. This shows the thoracic-abdominal fold and cleft (Ab. Ab. C.) previously referred to.
The sternal area between the latter and the stomodzum now lies next the egg shell, but soon
changes its position (Fig. 125, St. A.), owing to the forward growth of the thoracic-abdominal fold.
The labrum, here undeveloped, soon grows backward toward the latter, helping to bend the
@sophageal tube and probably slightly altering the position of the mouth (Fig. 125).

The proctodeum arises as a solid invagination of the epiblast, at a considerable distance behind
the abdominal cleft (Fig. 106, Pd.), in a stage intermediate between the embryos represented by
Pigs. 105, 106. A transverse section through the point of invagination is shown in Fig. 126, Pd.

The relation of the embryo to the rest of the egg can be seen in Fig. 108, which belongs to
the same species as Fig. 106. Besides the shell, which is unnaturally distended, the egg is sur-
rounded by a delicate embryonic membrane (Mb.). This membrane is secreted early by the super-
ficial epiblast, as shown by the fact that it does not conform with the thoracic-abdominal fold.

Wandering cells (Fig. 108, Y. C.) become gradually less abundant, but still continue to pass
to the outer surface of the egg next the epiblast. The transition from the wandering, amceboid
cell to the flattened mesoblast cell, lying close to the surface, can be best followed at this stage.

The fully developed egg-nauplius (Fig. 111) is about a week old. Embryos from the same
prawn vary slightly in size and in the degree of development, and also in the general character of
the cells. In some, the cells are larger and fewer in number, in others they are smaller and much
more numerous. The embryo is usually at one pole of the oblong egg. That represented in Fig.
111 is about one-eightieth inch long, and if the entire end of the egg were shown the drawing would
be nearly twice as large.

The relation of the embryo to the whole egg can be detérmined from Fig. 127, where the plane
of section is through the long axis of the egg, but through the short axis of the embryo. In the
course of development the egg increases appreciably in size and also changes its shape, at first being
spherical, but gradually becoming oblong. At this period the long axis of the embryo (using this
term fo apply to the more obvious embryonic tissues of the egg) is parallel with the short axis of
the egg, while in the course of growth the embryo spreads over one side of the egg, until its long
axis coincides with that of the latter.

The optic disks have become large oval masses of cells which project from the surface, and
inay now, for the first time, be appropriately called lobes. They represent the eye and eyestalk.
The blocks of cells (S. O. G.) in intimate relation with the optic lobes are the ganglia of the antenn:e,
and represent a large part of the future brain. The appendages are all simple, but a bud soon
grows out from the posterior sides of the second pair of antennie.

The right antenna is already bifid near its tip. A little later it has the appearance shown in
Figs. 109 and 110. Rudiments of the first pair of maxillie (Mx. I.) are also present. The ganglia
of the second pair of antennee are developed in close union with the ganglia of the antennules.
Together they form the supra-cesophageal ganglion or “brain.” The stomodeum (Std.) appears
from the surface as a distinet mass of cells extending behind the labrum (Lb.).

The thoracic abdominal fold, at first vertical to the surface, bends up and grows forward
toward the labrum, and a shallow groove which marks the median notch of the telson plate (Fig.
110) is formed at its extremity. The anus passes forward (backward in a morphological sense)
from its dorsal position through the median notch until, at a considerably later period, it comes to
lie on the ventral side of the fold near its apex. The mass of cells (H.) behind the anus probably
represents the heart. Near the mandibles and maxill, cells are seen with large granular nuclei.
These are cells which have migrated from the yolk to this part of the embryo. Nuclei of epithelial
cells are sprinkled over the entire surface of the egg, but increase in number as we approach the
embryo.

The section through the entire egg (Fig. 127) shows some of the general characteristics of the ege-
nauplius. The thoracic abdominal fold is here cut on a level with the anus, and lies in a wide shallow
groove. The yolk is composed of irregular blocks, only a few of which are represented, and con-
tains numerous wandering cells. Some of these (Y. ©.) are settling down on the yentral neryous

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 407

plate, while others (Y. C. Y. O.') have wandered far and wide through the yolk. The embryo is
raised considerably above the general surface of the egg and the shell more closely invests
the egg than shown in the drawing. The embryonic membrane is not represented.

Fig. 125 is a nearly median longitudinal section, and shows the relations of the thoracic-ab-
dominal fold, the cesophagus, and the ventral or sternal surface between them. The loose and
irregular arrangement of cells immediately below the surface is most marked, and also the granu-
lar nature of the nuclei which is such a constant character. Numerous degenerating cells (S. 8. C.)
are seen near the esophagus, and amcebiform cells can be traced from the thoracic abdominal fold
to the surface immediately behind it.

The structure of this embryo is illustrated more completely by a series of transverse sections
(Figs. 114-124), the first two of which (PI. x1, Figs. 114, 115) traverse the optic lobes, and the
third cuts the brain. The central mass of large cells which was noticed in the optic disks can no
longer be distinguished. The lobe (O. L.) is composed of similar cells with granular nuclei, the
superficial tier being somewhat the larger and columnar. In the brain the central cells are smaller
and stain more intensely than those at the surface (Fig. 116, 8. O.G.). Wandering cells (Y. C.)
can be traced in their passage from the yolk to the optic lobes, brain, ventral nervous plate, and
other parts of the embryo. Between the lateral halves of the brain there is a shallow median fur-
row (Fig. 116, M.F.). This is continued backward into the much broader and deeper depression in
which the convex ventral side of the abdomen fits (Pl. x11, M. F.). The three following sections
(Figs. 117-119) pass through the esophagus, and the ventral nerve thickening immediately behind it.

About the esophagus (Fig. 117, Std.) numerous chromatin balls (S., 8. C.) are seen in the yolk,
and a mass of cells (Mes.) is met with at the base of the appendage and within its fold. These
elements are derived from the wandering cells and must be regarded as mesoblast. The fold of the
appendage consists essentially of a single layer of cells. Those elements which enter it undoubt-
edly go to form the musculature of the limb while the cells of somewhat similar appearance, which
are derived from the ectoblast, represent the ganglia and nerves. On either side of the esophagus
the yolk has undergone important physical and chemical changes. The yolk spheres or blocks
are full of vacuoles and have a corroded and granular appearance, while in contact with the
embryonic cells there is a residue of small refractive granules. These vary considerably in size,
and some of them stain lightly in hematoxylin and represent the last stages in the degeneration
of chromatin. The eroded and altered yolk (A. Y. 8.) is represented in many of the sections.
Between the cesophagus and bases of the antenne the yolk is absorbed, leaving a protoplasmic
reticulum (Fig. 117, Ret.).

In Fig. 118 the mass of cells representing the mandibular ganglion (Md. G.) is sectioned, and
in the following figure, the mandibles themselves (Fig. 119, Md.). Numerous cells, both in this
and the following sections, are seen in the course of their migration from the yolk to join the
ventral nerve-thickening. The latter, which is the rudiment of the nervous system, is at this
stage scarcely thickened at all, on the middle line, below the level of the mandibles. Thus in Fig.
121 the buds of the first maxille (Mx. I.) are united by the primitive layer of epiblast. To this a
single migrating cell has attached itself on the middle line. Migrating mesoblast cells (Mes.) also
pass into the fold of the appendage, and others (Fig. 120, Mes.) take up a position against the
epiblast of the body wall. The nuclei of the latter stain intensely and become flat, spindle shape
in section, and probably represent the nuclei of muscle cells.

The structure of the abdomen at this stage is shown in Figs. 120-125. The body wall of the
dorsal side consists of a single layer of columnar epiblast, while the ventral wall is thickened.
The hind gut (Fig. 122, Hg.) is a tube, the wall of which consists of a single layer of cells. It is
laterally compressed so that the lumen is hardly appreciable. The intervening cells (Mu.) largely
represent the rudimentary flexor and extensor muscles of the abdomen. A comparison of Figs.
123 and 125 shows that cells extend from the thoracic-abdominal fold on all sides into the yolk.

The cells at the surface in Fig. 124 have come mainly from the yolk (H.) and are in the posi-
tion where the heart is subsequently developed. Cells approaching the surface in this region are
very clearly shown in Fig. 125 (Y. C., Y. C.'), which is a section through a somewhat younger
embryo.

The wandering cells, as we have seen, abound in the parts of the yolk nearest the embryo. The

408 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

nuclei have the usual characteristics—irregular shape and granular contents. They are sur-
rounded by a small irregular body of protoplasm which does not readily stain and which is often
difficult to observe. In PI. xx1x, Fig.33, several of these wandering cells are seen greatly enlarged.
Sometimes, as here, the perinuclear protoplasm appears to join that of neighboring cells, but in most
cases there appears to be no such connection between them.

The endoderm, though not represented in the drawings, makes its appearance as a distinct cell
layer at this time. In an embryo a few hours older than that represented in Fig. 125 the endo-
derm has the form of a narrow sheet of rather large cells, between the yolk and the rudimentary
heart, near the body wall. In the space corresponding to the heart, blood corpuscles can already
be detected, besides scattered mesoblastic cells. Both the latter and the entoblast are derived
from the wandering cells which come out of the yolk.

STAGE VII.—RUDIMENTS OF SEVEN PAIRS OF APPENDAGES.

Fig. 110 represents a phase intermediate between the egg-nauplits (Fig, 111) and the present
stage (Fig. 130), and is of special interest for the light which it throws on the history of the wan-
dering cells. The structure of this embryo is illustrated by Pl. xxiv, and Figs. 136, 137, 144, 145.
Fig. 137, which represents a section just behind the base of the first antennze (A. I.), may be com-
pared with Fig. 117. Numerous yolk elements are found in the vicinity of the csophagus, where,
as will be seen (Fig. 154, Mu.), they become speedily converted into muscle cells and somatic meso-
blast. In Fig. 136 several wandering cells attached to the body wall, have all the characteristics
of blood corpuscles, a deep staining granular nucleus, and a clear irregular cell body. The blood
cell and muscle cell are both derived from wandering mesoblasti¢ cells, and in the early stages of
their metamorphosis they resemble each other, so that it is not always possible to distinguish
them. Undoubted blood cells, however, have already made their appearance.

Figs. 144, 145 show that the yolk is pervaded by a great number of cells. These originated in
the way described, chiefly by migration from the ventral plate and thoracic-abdominal fold, and
also by subsequent multiplication in the yolk. At this period some of the cells migrate to the pole
of the egg opposite the embryo and apparently assist in forming a conspicuous dorsal plate (Dp.).
In this embryo they have not quite reached the surface. A structure is eventually formed which
reminds one of the “dorsal organs” of various Crustacea. This and the wandering cells “will re-
ceive further consideration later on. :

The embryo of Stage VII is represented in Fig. 130, Pl. xxiv. Figs. 111, 109, 110, and 130
form a consecutive series of embryos, each but a few hours older than the preceding. In the first
(Fig. 111) the optic lobes, first and second pair of antennz, and mandibles are all simple appen-
dages, and are quite similar in general appearance. The abdomen and part of the thorax are
represented by a simple fold, the thoracic-abdominal fold. In the second embryo (Fig. 109) the
parts are more compact and the second pair of antennwe are forked at their tips. In the third
phase (Fig. 110) the optic lobes and abdomen exhibit the most rapid growth. The former are
drawn closer together and arch outward from the middle line. The anus is dorsal. The abdomen
extends forward until it nearly meets the labrum and has a slight groove or depression at its ex-
tremity. All the appendages have assumed a more oblique position with respect to the long axis
of the body, and the second antennz are now the largest.

In the fourth phase (Fig. 130) we see the same changes carried still further. The optic lobes
are large convex disks which join each other on the middle line and are ntimately united to the
brain. The anus is terminal. On at least the first pair of antenne hairs are developed, although
there is not perhaps so marked a contrast between the first and second antenn in this respect as
would appear from the figure. The first and second maxille and the first and second maxillipeds
are present as rudimentary buds.

The general structure of the embryo (Figs. 129, 131) agrees with that of preceding stage.
The embryonic tissues consist of cells of various sizes and shapes, from quite large cells down to
particles no larger than the balls of chromatin which are suspended within the nucleus, and from
the spherical to the lens-shaped, spindle-shaped,and wedge-shaped forms. Generally all the nuclei
agree in containing coarse grains of chromatin or nucleoli. These vary much in size and number
in different nuclei according to the condition of the cell. In degenerating nuclei, the chromatin
residue is aggregated into fewer and larger masses.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 409

Wandering cells are now scattered throughout the entire egg. They occur in abundance both
in proximity to the embryo proper and on the sides of the body walls, and especially in the region
immediately behind the thoracic-abdominal fold.

Pig. 131 is a median longitudinal section through an embryo like that shown in Fig. 130. The
outer or superficial cells are generally columnar and have distinct boundaries. Their nuclei are
spherical, elongate, or wedge-shaped. They divide in both planes, but most commonly in the
plane perpendicular to the surface. When we compare this section with the similar one (Fig. 125) of
the preceding stage the most striking difference is the great increase in the length of the thoracic-
abdominal fold and the ventral thickening of the nervous system. Some of the cells of the latter
next the yolk (Mes.) are flattened and spindle-shaped. They have recently come from the yolk
and joined the nervous system, and it is possible that these and similar cells represent primitive
connective tissue envelopes. :

In a more lateral section (Fig. 129) the optic lobe is seen to consist of two portions, a super-
ficial layer of large. cells (O. I.) and a deeper layer (G. L.). The first is continuous with the
general epiblast over the surface of the body. Its cells multiply in both planes, and some of them
pass below to join the deeper layer. The cells of the latter multiply by the usual mitosis and also
receive accessions from the yolk. The plane of section passes through the equatorial plate of one
of these dividing cells. Some of the cells next the yolk (Mes.) are flattened like those just described
in the ventral nervous thickening, but this condition appears to be somewhat transitory. The
outer layer of the optic lobe may be regarded as a retinogen, since from it, or from a layer corre-
sponding to it, the visual apparatus of the eye is developed, while from the deeper layer or gangliogen
the optic ganglia of the eyestalk are formed.

A comparison of the transverse sections (Figs. 128, 132-135) with corresponding sections of
the previous stage (Figs. 115, 117, 121, 124) shows some interesting changes. The brain is larger
and more compact, and some of the cells next the yolk are flattened (Fig. 132, Mes.) and bear a
resemblance to muscle or connective tissue cells. They originate from the cells marked Ct. 8. in
Fig. 116, and come from the yolk. Like the cells already mentioued in the optic lobes and ventral
nervous system, they seem to represent a rudimentary perineurium, but, as a well-developed covering
of the nervous system is nof present until a considerably later stage, they are probably transitory.
Fig. 134 corresponds closely with Fig. 117. It shows the section of the cesophagus and of the
ganglia of the second antenne. In the younger stage the ganglion (seen to the left in Fig. 117,
at the base of the appendage) is a small, loose mass of cells associated with the surface epiblast,
while in the older embryo it is in contact with the wall of the esophagus, is more compact, and its
cells are somewhat differentiated. The central nuclei are smaller and stain most intensely. The
esophagus (Std.) is saspended to the body walls by rudimentary muscles (Mu.), the cells of which
are much elongated. They are derived from migrating mesoblastie cells like those seen in the
earlier stage (Fig. 117, 8. C.), or like the one shown in this figure to the left of the esophagus.
Fig. 137, which is from a stage intermediate between the two just considered, gives additional
evidence of this réle of the wandering cells. Fig. 128 furnishes a very interesting comparison with
Fig. 121, In the latter, cells abound in the yolk adjoining the rudiment of the ventral nervous
system, which is represented by the primitive epiblast on the middle line. In the older stage
scattered mesoblast cells are greatly reduced in number and the ventral thickening is very
marked. Cells of recent derivation from the yolk (Mes.) at the base of the appendage can also be
distinguished. ?

In Fig. 133, as in Fig. 124, the plane of section is just behind the thoracic-abdominal fold.
Here we recognize a tier or plate of tall, columnar cells (End.), the nuclei of which lie at the deeper
ends of the cells or on the side away from the yolk. In the presence of these bodies the food yolk
(Pig. 135, A. Y. S.) is absorbed or converted into a granular residue. This layer represents the
entoblast or the epithelium of the mesenteron already described. Numerous wandering cells are
encountered (igs. 124, Mes.; 135, Y.C.), which take up a peripheral position, and from the first are
closely associated with the epithelium of the hindgut. They unite the mesenteron to the hindgut,
and it is impossible to say exactly where the one begins and the other ends. Between this ente-
blastic plate and the surface epiblast (Ect.) numerous cells are interpolated (Figs. 133, 135, Mes.),
which are undoubted mesoblast. They are directly continuous with the layer of mesoblast (Fig.

410 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

128, Mu.) which extends throughout the abdomen between the hindgut and body wall. Mesoblast
cells derived from the yolk (Fig. 129, Mu.) are also seen underneatb the epiblast on either side
of the body. ‘Lhe nuclei of these cells stain very deeply, and the cell protoplasm is prolonged
into a short fiber or forms an irregular body. In the latter case the cells have the appearance of
blood corpuscles. ,

The heart originates in the mesoblast (Fig. 135, Mes.), between the entoblast and outer wall
of the body, just behind the thoracic-abdominal flexure.

At this time fibrous substance (punktsubstanz) is first seen in the brain. It appears as two
small masses joined by a transverse commissure, in a plane just anterior to the roots of the first
antenne. Itis distinctly fibrous and apparently originates from the protoplasm of surrounding cells.

STAGE VIII.—SEGMENTATION OF THE NERVOUS SYSTEM—AT LEAST EIGHT PAIRS OF APPEN-
DAGES PRESENT.

We have two longitudinal sections (Figs. 138, 139) to illustrate this stage. If we ‘compare
the latter figure with the corresponding one of the previous stage (Fig. 131) we see at a glance.
that a long step forward has been taken in development. Between these, 1 have obtained one
intermediate phase, which is a trifle older than the embryo given in Pl. xLIv, and ean be best
described by showing in what respects it differs from it.

The rudiment from which the nervous system is formed (Stage Vit) is a plate of cells extend-
ing from the optic lobes to the apex of the abdomen. Anteriorly in the brain (Fig. 132) it is very
thick, but gradually thins out as it is followed backward, until it consists of a single layer of epi-
blast at the very tip of the abdomen. In the phase intermediate between Stages vil and vill the
portion of nervous thickening between the @sophagus, which passes through it, and the thoracic-
abdominal fold is partially segmented into cell masses, the primitive ganglia.

The cells of this ectoblastic thickening may be roughly divided into a surface layer, the nuclei
of which are large and contain diffuse granules of chromatin, and a deep cell mass with smaller nuclei
which stain more intensely. Similarly in the optic lobe we find a thick pad of uniform, deeply
stained cells (gangliogen) next the yolk, and separated from this a well-marked surface layer (reti-
nogen) of larger cells. The superficial, epiblastic cells on the inner or ventral side of the thoracic-
abdominal fold are large and columnar. The nuclei are very much elongated and closely crowded
together, and lie at all levels. This implies rapid cell division in this layer in a plane perpen-
dicular to the surface, and as a result of this, the thickening of the ectoblastic plate in this region,
such as we see in the next phase (Fig. 139).

Near the apex of the abdomen there is a transverse zone of very large cells, and the smaller
superficial cells adjoining it are arranged in parallel lines. Something resembling this was noticed
in Stage vi (Pl. xLu, Fig. 120, B. Z.). It corresponds to the budding zone ([nospungszone) which
Reichenbach figures and describes in the crayfish. He detects it in a very early stage (Stage E,
embryo with rudiments of the mandibles, corresponding nearly to Stage V of this paper), and finds
that it consists of a transverse zone of cells containing large nuclei at the extremity of the abdo-
men, below the notch of the telson. From it the segments following the mandibular segment are
Praddaule budded off.

~ The present stage is characterized by the segmentation of the nervous system aaa the great
development of the optic lobes. The ventral nerve plate is blocked out by lateral constrictions
into its component ganglia. There is also a median vertical ingrowth or constriction which tends to
divide the plate into a double cord. It is, however, discontinuous at the middle of each bloek, so that
the ventral nervous system consists of a double chain of ganglia, each pair of which are united by a
transverse commissure or band of cells, and each ganglion is similariy joined to the one behind or
in front of it. Distinet commissures pass from the brain around the cesophagus and unite the
former to the ventral nerve chain. The first pair of post-oral ganglia contain two masses of fibrous
substance united by transverse fibers as in the brain. The ganglia following these also contain
punktsubstanz. It is developed as a small isolated mass on the dorsal side of each ganglion,
toward the middle line. As development proceeds these masses increase in size and are grad-
ually united by transverse commissures in each pair of ganglia (Pl. XLVI, Figs. 150, 151, Pk.).

A mass of fibrous or granular substance appears in each optic lobe in the gangliogen next the
brain. Fibers pass from it to the punktsubstanz of the brain, which sends fibers down to the

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 411

cireum-cesophageal commissures to the first post-oral ganglia. The fibrous masses unite on either
side of the ventral chain to form a double longitudinal commissure. Thus at an early stage the
optic lobes, brain, and ventral nervous system are intimately connected by fibrous tissue.

All the segments of the body are now marked off as seen in Tig. 159. The first post-oral
segment is the mandibular (g. 1v), and following it are the segments of the maxille the maxilli-
peds and the first pereiopod. The second thoracic ganglion lies in the angle made by the
thoracic-abdominal flexure. The third, fourth, and fifth thoracic, and the six abdominal segments
constitute the thoracic-abdominal fold.

In the superficial parts of the brain large elements are met with which multiply by mitosis,
but have a distinct histological character. They consist of a large spherical nucleus containing a
diffuse chromatin network, and a granular cell body without definite wall. They are the ganglion
cells, whieh are abundant in all later stages.

The optic lobe consists of two sharply distinguished parts already mentioned, the retinal and
ganglionic portions. The retinogen which forms the eye is a superficial disk of cells resting like a
cap on the other part of the lobe, thickest on the outer side of the lobe and rapidly thinning out
toward the middle line to a single layer of cells. The nuclei are elongated and wedge-shaped, and
cell division takes place commonly in a plane perpendicular to the surface, corresponding to the
long axis of the vertical nucleus. The gangliogen consists of a deeper portion next the brain,
coutaining a ball of fibrous tissue, and a part next the retinogen or eye rudiment. Below the thick-
est portion of the eye the cells have large nuclei, which show a tendency to arrange themselves in
rows radiating from the deeper half of the lobe. These large, clearer cells also extend down to
the food yolk, and in lateral longitudinal sections (Fig. 138) form the inner stratum of the lobe.
The cells which lie between them and the eye, here one cell thick, are smaller and stain intensely
(v. Section Ix).

The heart (Fig. 139, 7) is now a broad and greatly flattened chamber between the body wall
and endoderm (Hnd). It extends forward a considerable distance between the epiblast and yolk,
and is continued backward into the superior abdominal artery (A. a. s.). It is filled with serum
and blood corpuscles.

The endoderm is a more conspicuous layer (Hnd.), and the wandering cells are reduced in num-
bers. They are still seen in all parts of the egg, approaching the body wall, the nervous system,
the endoderm plate, and other parts of the embryo (Fig. 139, y. ¢.).

STAGE LX.—EMBRYO WITH EYE PIGMENT FORMING.

A sketch of the embryo at the time when eye pigment has already formed is shown in Pl.
XLVI, Fig. 158. The optic lobes are huge pear-shaped masses meeting on the middle line in
front and arching outward and backward on either side of the brain. The ocular pigment appears
as a thin, dark-brown crescent near the outer surface of the lobe. Pigment is first formed at the
posterior end of the lobe nearest the base of the antennules, and spreads upward over its larger
convex end. The brain is constricted into two portions corresponding to the antennular and
antennal segments.

The segments of the abdomen are faintly marked off at the surface, and the telson plate which
overlaps the mouth, is deeply forked at its extremity. (Compare with spatulate telson of the first
larva, Pl. xx1, Fig. 9.). The plumose setz which garnish the posterior edge of the telson are now
represented by short stumps.

The first pair of antenne are stout, simple appendages, tipped with sets and folded backward
along the sides of the body. The second pair of antennze just inside of the latter, are biramous.
They are also hairy at the tips, and the embryonic membranes surround them like the fingers of
a glove. °

The present stage is illustrated by Pls. XLVI and xLyil. The drawings are made from different
embryos, all of which are of the same age, excepting those represented by Figs. 152, 155, 159, and
161, which are a trifle more advanced.

In the first series (P]. xLv1, Figs. 146-151) the pigment cells are just forming in the eye. They
are first developed in the thickest part of the retinogen next the food yolk. A single section, like

412 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. |

Fig. 146, shows the complete history of development of the retinal layer from its one-celled con-
dition toward the median line (already seen at an earlier stage, Fig. 136, Stage vi) to the point
farthest from the middle line, where pigment is formed. The fibrous nerve tissue of the gan-
liogen now consists of three masses, a ball nearest the brain, which is the first to appear, and two
smaller masses between it and the retinogen. Huge ganglion cells (ge.) are of frequent occur-
rence, especially at the surface of the eye stalk next the brain. (The details of the development
of the eye are reserved for a special section.)

The brain at this time (Figs. 146-148) differs from that of the previous stage chiefly in point
ot size. It is composed of nerve cells and large ganglion cells (ge.), which oceur chiefly near the
outer surface, and central fibrous tissue. It rests against the food yolk, and in the living embryo
it is bathed with a current of blood (B.S.). The fibrous tissue of the brain has the form of a letter
H with a wide and short transverse bar. In front of the transverse commissure (Fig. 147, Tc.)
the fibrous substance is prolonged on either side into the optic lobes; bebind, it extends down to
the ventral nerve cord, on the inner side of the esophageal ring (Fig. 148, oem.).

The ventral nervous system, like the brain, is bathed with blood, which fills a large sinus
between it and the yolk. This communicates with extensive blood sinuses extending along the
sides of the body (Figs. 148-154, B. S.). In some cases the food yolk, usually in an altered or finely
divided state, is in close contact with the nerve chain (Fig. 157). Cells extremely flattened and
spindle-shaped in section, are found in small numbers closely applied to the nervous system (Figs.
152, 157, pr.), and forming a rudimentary perineurium. In most cases they are undoubtedly iso-
lated cells, and do not constitute a membrane. They originate from the wandering cells and
correspond to cells similar in shape and origin which appear between the yolk and nervous system
at a much earlier period (Stage VII, Fig. 151, Mes.). The brain and ventral cord are not as yet
differentiated from the superficial epiblast, but anteriorly, flattened epiblastic cells begin to appear

between the nerve cells and cuticle. Ganglion cells (Fig. 150) also make their appearance in the -

cord, commonly at either side, close to the surface.

There is direct continuity of fibrous substance in the optic lobes, the brain, and the ventral cord
as far back as the abdominal ganglia. In the latter this substance has not been developed. In each
single ganglion there is a ball of this tissue which is united to its fellow in the same segment by a
transverse commissure (Fig. 151), and to the preceding and following ganglion by longitudinal com-
missures. It is as a rule completely inclosed by the ganglion cells, but is separated from the yolk
or blood sinus often by a unicellular layer (Fig. 150), and in the antennular and antennal segments of
the brain (Figs. 147, 148) the cells next the yolk are discontinuous. In the ecircumc@sophageal cords
the fibrous tissue also is without a cellular cortex on its inner or central side (Fig. 149, fs.). With
slight changes these relations are maintained in the hatched larva (see Pl., Lv., Figs. 220-222).
The foregut is at this time a tube with definite walls and wide lumen (Figs. 148, 152, fg.). At
abour its middle it is bent abruptly backward on itsel£in an acute angle. The first portion, lead-
ing from the mouth to the angle, is the esophagus and is directed forward; the hinder blind end of
the tube lies in nearly a horizontal plane, and represents the masticatory stomach. The walls of
the foregut consist of a single layer of columnar cells with large nuclei. They end abruptly next
the yolk, but the cavity of the tube is screened from the latter by a thin membrane of flattened
cells. A sheet of elongated or spindle-shaped cells surrounds the wall of the foregut and extends
over the nervous system (Figs. 148, 149, Mes.), while just below the cesophagus and behind the
mouth a bundle of elongated cells grows over the nerve cords to the roots of the mandibles repre-
senting the adductor muscles, which become so prominent in later stages. These relations are
easily deciphered in the structure of an earlier embryo (Stage vi1, Fig. 134), where we have already
seen muscle and connective tissue elements, derived from the wandering cells, extending from
the w@sophagus to the epiblast of the body wall.

Wandering cells also pass into the blood sinuses from all parts of the egg, and become
converted into blood cells and connective tissue elements. In Fig. 148 we see two such cells on
the edge of the blood stream, and in Fig. 152, (yc.) several of these bodies are in contact with
the blood current on the side of the egg opposite the embryo. The relations of the epiblast, wan-
dering cells and blood corpuscles in this part of the egg are seen in detail in Fig. 161, where a single
large wandering cell is already half submerged in the blood. The various other drawings illus-
trating this stage (Figs. 154, 155, 160, yc.) point to a similar fate for a portion of the wandering

MEMOIRS OF THE NATIONAL AOADEMY OF SCIENCES. 415

cells. This subject of the réle of the wandering cellg in Alpheus is one of the most difficult and
at the same time the most interesting which has been met with in the study of its life history,
and a full discussion of it is reserved for another part of this paper (Section v1).

A new sfructure, the carapace (Figs. 148-151, 160, ep.), is seen for the first time at this period.
It takes the form of a lateral longitudinal outgrowth of ectoderm on either side of the body in the
region of the thorax. These longitudinal folds represent the branchiostegites, which form the outer
wall of the branchial cavity. In Fig. 160 the structure of the rudimentary carapace and the way in
which it originates is very clearly shown. The epiblast cells at the surface multiply and the cell
protoplasm is prolonged downward into long strands or spindles. Meantime the ectoblast is
pushed outward along definite lines and the spindles of one side of this fold unite with those of
the side opposite, thus forming a framework of transverse beams or pillars. Blood enters the
fold, which thus becomes a respiratory organ. This structure is essentially maintained up to lar-
val lite (v. Fig. 195).

The hindgut or intestine (Figs. 150, 157, Hg.) has a considerably larger lumen than in the pre-
ceding stage, but its histology is essentially the same. The walls are composed of a single tier of
large columnar cells. The cell protoplasm is granular, and projects into the lumen of the tube,
and the cell wall is usually distinct. There is an outer investment of mesoblast as in earlier
stages, which is closely associated with the surrounding cells of the developing abdominal muscles
(Figs. 150, 160, mu. f.). The muscle fibre appears as an outgrowth of the cell protoplasm of the
muscle cell. The nucleus elongates until it becomes rod-shaped. The fiber is homogeneous,
nonstriated and stains feebly in borax carmine, but not at all in hemotoxylon. The intestine com- |
municates with the midgut or the cavity which contains the great mass of food yolk, and with
the exterior by the anus, which is on the under side of the telson plate opposite the labrum.

Fig. 157 shows the continuity of the epithelia of the hind and midguts, and illustrates in a very
satisfactory manner the origin of the endoderm. Histologically the entoblastic cells resemble
those of the adjoining epiblast, and it is impossible to draw a sbarp line between them. The
endoderm cells are vesiculated, have less definite boundaries, and extend pseudopodia-like pro-
cesses into the yolk. The endoderm begins near the point marked vac. Fig. 157. Here the lumen
of the tube enlarges, and the endoderm extends forward over the flexure of the nerve cord and
upward over the sides of the body. Posteriorly it is separated from the body wall by the blood
sinus which represents the heart and its arteries (H). The yolk next the endoderm is eroded and
granulated. The formation of the endoderm thus begins near the abdominal flexure, in the egg-
nauplius stage, at the point where the hindgut communicates with the cavity of the mesenteron,
and advances gradually forward on all sides. It is composed of cells (Fig.157, y. c.) which migrate
from the yolk and assume an extreme peripheral position with respect to it. They eventually
acquire cell walls, unite and inclose the yolk which they continue to feed upon, apparently by first
producing chemical changes in it and then absorbing its particles. In the early stages the
mother cells of the endoderm and mesoderm can not be distinguished with certainty. However,
since the endoderm originates as a distinct epithelial layer behind the ventral plate, and thence
spreads forwards, slowly walling in the mesenteron, it is obvious that the bulk of the anteriorly
wandering cells are mesoblast. ;

The extensive blood sinuses which are now present have already been mentioned. In the
angle between. the optic lobes in front, there is a large blood space (Fig. 152, b. s.), and blood
passes from the heart upward and forward nearly around the egg in a thin irregular stream
between the skin and food yolk. Mesoblast cells grow forward, from the abdominal region and
line the outer sides of the endodermal wall, and extend upward to a thin sheet between the yolk
and the epiblast. Endodermal cells coming from the yolk attach themselves to this layer. The
pulsatile chamber of the heart is not a very definite structure at this stage. It lies above the

endoderm, nearly opposite the angle of the thoracic-abdominal fold. Its walls are delicate, and
appear in sections as thin strands of mesoderm cells. The nuclei are elongated and the cell proto-
plasm is produced into long processes. The pericardial space surrounding it is filled with blood.

In Stage vil (Figs. 144, 145, Dp.) we noticed an extraordinary migration of wandering cells
to the pole of the egg opposite the embryo. These cells eventually reach the surface aud rein-
forcing the primitive epiblast, give rise to a conspicuous dorsal plate, which is shown in Fig. 153
(Dp.). This is from an embryo intermediate between Stages vit and Ix, in which eye-pigment

414 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

is not yet formed. The plate is slightly thickened at its center, where there is an inconspicuous
pit marking the point of ingrowth. As the invaginated cells pass into the yolk they degenerate,
giving rise to spore-like particles which spread in incredible numbers through a large part of the
egg. Some of the wandering cells in this region doubtless degenerate before reaching the surface.
A part of a similar section is shown in more detail in Pl. v, Fig. 36. The particles vary consider-
ably in size, stain uniformly and intensely and the yolk about them is granular or finely divided.

Ata corresponding stage in the lobster (Homarus americanus), I have observed a large diffuse
pateh of cells which probably answers to the structure just described. In this case the embryo rests
on the side of the oblong egg and the cell plate is at one end of it, at a point about 90° behind the
embryo. This position seems to be quite constant, while in Alpheus the plate is nearly opposite
the embryo, at the stage when it is most conspicuous.

STAGE X.—EMBRYO WITH EYE-PIGMENT STRONGLY DEVELOPED AND THE POSTERIOR LOBES
OF THE GASTRIC GLAND FORMING.

All the thoracic limbs and the sixth pair of abdominal appendages are present in a rudimentary
condition. The abdomen has grown forward until the tip of the telsou now extends beyond the
optic lobes. The embryonic telson is fringed with seven pairs of setw, and resembles the larval
telson, except that the median notch is deeper. Seen from the exterior the eye-pigment has the
form of an oval disk.

The longitudinal section, Pl. xLy111, Fig. 168, shows most of the important changes which have
occurred since the last stage. These chiefly concern the eye, the nervous system, and the midgut.

The ectodermal pigment cells (retinular cells) of the retinogen have spread inward until they
cover its whole inner convex surface (PI. xLvu1, Fig. 167). Near the outer surface of the eye the
erystalline cone mother cells (ce) can be recognized, and between the eye and the ganglia of the optic
lobe there is a narrow space which communicates freely with the blood sinus (B. S.) on the outer side
of the lobe. Wandering cells are frequently seen rear this blood sinus, and in the space between
the eye and ganglia flattened cells also occur, which find their way in thither from the yolk. In
the optic lobe another fibrous mass has developed near the eye (Fig. 164-7). In horizontal section
(Pl. xLvu1, Fig. 159) the relations of the fibrous tissue of the brain and optic lobes is clearly shown.
In each lobe there is a chain of four fibrous masses united by a stalk of fibers to the anterior
or optic swelling of the brain (of). ;

The structure of the brain (Figs. 159, 169, 170) begins to approach in coviplexity that of the
larva, which was described in the first section of Part 11 of this paper. The lateral fiber-balls, so
conspicuous in the later stages have now appeared (Fig. 159 and Pl. x~rx, Fig. 174, if). They are
developed in close union with the large central fibrous mass, which supplies the optic lobes, and
probably belong primarily to the antennular segment. Below this and nearer the middle line there
is a less definite fibrous center (g/.) which supplies the antennal segment. With this, the cso-
phageal commissures are directly continuous (Figs. 171, 174 ocm.).

The complete chain of ventral ganglia can be seen in Fig. 168. This section is not pertectly
median, but cuts a fiber-ball of each ganglion. The skin or hypodermis is now differentiated
from the nerve elements and consists of a thin layer of flat cells. The fibrous masses of the gan-
glionic ehain are also imperfectly surrounded by peculiar cells, the nuclei of which are spindle-
shaped in section. These also occur in the brain, and in either case must be regarded as metamor-
phosed ectoderm cells, or more probably as intrusive mesoblast. A transverse section of the nerve
cord in the thoracic region is shown in Fig. 172, and corresponds very nearly in plane of section
with Fig, 151 of the last stage. The fusion of the ganglia is now more complete, and the fibrous
balls and commissure are relatively larger. (Compare with this, Fig. 176, a section of the thoracic
ganglion of thelarva.) Inthe abdominal ganglia the fibrous elements have essentially the same
relations, but lie at a deeper level, being separated from the adjoining tissues by at most a single
layer of nerve cells. In Fig. 168 we see that the yolk comes in close relations with the nerve
cord behind the @sophagus to the endodermal fold (7) near the point of union of the mesenteron
and hindgut. Wandering cells approach the cord and become flattened against it, as already ob-
served in much earlier stages. : ;

>

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 415

The two divisions of the foregut, @sophagus, and masticatory stomach, have the relations
already described. The wall consists of a single layer of tall columnar cells. In the masticatory
division the wall has begun to thicken next the yolk screen, its cells being cuneiform, and the
nuclei élongated and crowded below the surface. From the anterior wall, muscle or connective
tissue cells extend forward under the brain.

POM

mg!

Fic. 1.—Diagrams of transverse sections through the alimentary tract of an embryo of Alpheus saulcyi which is
nearly ready to hatch, to show the origin of the gastric gland from the posterolateral lobes of the midgut. Section
Lents the hindgut and lobes of the “liver,” Section 11 the hindgut where it merges into the meseuteron. gg', gg’,
Secondary lobules of mg!; HG, hindgut; mg', postero-lateral lobes of midgut.

HG HG HG
Il

The development of the mesenteron can be understood by reference to Figs. 162-165, 168, and
185. The endodermal epithelium spreads by the division of its own cells and by accession of cells
from the yolk, both forward over the nervous system and upward against the sides of the body.
This is shown in the series of horizontal sections (Fig. 162-165). Fig. 168 which is from an
embryo a little more advanced, shows that the endoderm is rising from the nervous cord near its
point of flexure, into a transverse vertical fold. Simultaneously with the upward growth of this
ventral fold, two dorsal longitudinal folds grow downward, and\finally unite with the ventral fold
and with each other, thus constricting off from the alimentary tract two lateral pouches, the pri-
mary lobes of the “liver.” The folds grow forward and the constriction proceeds gradually with
the growth of the embryo. This process is illustrated by the diagrams (Fig. 1) which were drawn
from an embryo near the point of hatching. The histology of the endoderm as shown in Fig. 173,
is essentially the same as in the previous stage. The cells are prismatic, and the nucleus spherical,
and, as in all stages, filled with numerous nucleoli or chromatin balls. The cell walls are very
delicate and the protoplasm often contains large vacuoles.

/ i
1 2 i } .
99 dy ang? mo, FS.

Fic. 2.—Semidiagrammatic representation of the alimentary tract and its appendages in the
first larva of Alpheus saulcyi. The middle line of the body is also shown. FS, foregut ; gg 1-3,
secondary lobules of postero-lateral lobe of midgut; HS, hindgut; mg, midgut; mg 1-3, an-
terior, lateral, and postero-lateral divisions of midgut; mo, mouth.

_/— 7

1S Cee ean med el ores

416 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Wandering cells still occur in all parts of the yolk, though in far less abundance than in
earlier stages. We find numbers of them moving toward the periphery, or next the body wall to
take part in forming the endoderm. The epiblast is conspicuous in Fig. 168 just in front of the
optic lobes. This corresponds in-position with the dorsal plate (Fig. 153 dp.), and is probably a
remnant of it. The small clusters of cells beneath it and the degenerative products which occur
near them, probably also represent the remains of the great swarm of degenerating chromatin
particles which was formerly present in this region. A blood space (Fig. 168,) now extends over
the dorsal side of the egg between the epiblast and the yolk, from the heart to the optic lobes and
region of the head.

Auteriorly we can distinguish in transverse section three vessels—a median impaired one,
which answers to the ophthalmic artery, and a pair of lateral vessels, the antennary arteries.
The vascular walls are extremely delicate and contain flattened cells, the nuclei of which in longi-
tudinal sections appear almost linear. Seen from the surface of the egg the blood vessels have-
the appearance of two bands of tissue, passing backward from near the point of union of the
optic lobes. Between and at either side of the optic lobes, and beneath and to each side of the
brain, we find blood spaces packed with corpuscles (Figs. 166-169, B. 8.) It is not possible, in
most cases, to distinguish at this phase true sinuses (veins) from arteries. The structure of the
heart is shown in Figs. 164 and 168 (#.), and is essentially the same as in Stage 1x

In Fig. 173 there is a small solid cluster of peculiar cells (R. O.) on either side of the alimen-
tary tract, between it and the heart. This I regard as the rudiment of the reproductive organ.
The cells are clearly differentiated from the surrounding cells. The nuclei are very large, spher-
ical, and stain lightly and diffusely. They are enveloped in a capsule of mesoderm cells, like those
forming the walls of the heart, and they originate from similar elements. In Stage rx (Fig. 157)
these cell masses were first recognized. They are then distinct from the surrounding elements,
and the nucleus contains a very delicate reticulum. Each cell cluster is so small that unless the
sections are uniform and complete it is very easily overlooked. The muscles have developed in
various parts of the body (Figs. 168, 171, 172, mw., mu. f., mu. €., g. m. a.), but most striking at
this stage are the great flexor and extensor miele of the abdomen.

The green gland (Fig. 170, A. G.) is another organ which we now meet with foe the first time.
It is an irregular tube, closed at both ends, and lies at the base of the second antenna, extending
up a short way between the body wall and brain. In the previous stage all the tissue at the root
of this appendage is very loose and reticular, and no lumen can be seen. I have been unable to
detect any opening of the gland to the exterior, nor should we expect to find any, since, as we
have already seen in Section I, there is none in the larva. It must be regarded as a mesodermic
structure.

STAGE XJ.—EMBRYO OF ALPHEUS HETEROCHELIS NEARLY READY TO HATOH.

The later stages (Stages vI-x) have had reference to a single species of Alpheus, namely,
Alpheus saulcyi, the larva of which is described in the first section. The embryo of Alpheus
heterochelis at about the time of hatching is considerably less advanced than the embryo of the
first species at a similar period, and will serve in many respects as a convénient connecting link
between the larva described in Section I and the last stage. The embryo of Alpheus heterochelis is
represented by a longitudinal vertical section and by a series of transverse ones (Pls. L, LI). The ~
longitudinal sections of Stage x, of this stage, and of the larva (Figs. 168, 180, 196), form a very
interesting series for comparative study.

The eye and the ganglia of the eye stalk (Figs. 177-179, 187) have become highly specialized,
and closely resemble the adult organs. The brain 1s larger, but shows no new structures which
have not already been noticed. The entire nervous system is more compact, and is completely
separated from the skin. The foregut is larger than in the previous stage, and the walls
of the masticatory stomach have become very much thickened. It is sereened from the yolk
by a membrane composed of large cells, which extend backward over the nerve cord. A double
band of muscles (Figs. 168, 180, g. m. a.) passes upward from the anterior wall of the masticatory
stomach and from the brain, to the body wall. These will be referred to the anterior gastric
muscles.

t

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 417

The mesenteron (mg.) is very largely reduced in size and is filled with a granular coagulum,
and, anteriorly next the head, with vesiculated and eroded remnants of yolk. The endoderm lines
all but the anterior third of this cavity, extending farther forward on the dorsal wall. A few
wandering cells are still presentin the peripheral parts of the cavity next the advancing edge of the
endoderm. Those elements, represented in Fig. 182, prove to be endoderm cells mechanically
detached from the wall of the mesenteron. The primary lobes of the midgut (“liver”) are larger
but otherwise similar to those described in Stage x. The endoderm cells are greatly vesiculated,
and the cell protoplasm has often a striated appearance.

The heart (Figs. 180, 186, H.) has undergone very considerable changes since the period repre-
sented by Figs. 164, 168. It is no longer dorso-veutrally flattened, but in transverse section it is
triangular in appearance. One side of the triangle is toward the intestine and one apex next the
body wall. Its suspension in the pericardium is very delicate. The ectoderm cells send down
spindle-shaped processes (Fig. 186), the Hcetoderm pfeiler of Reichenbach, and to these, meso-
dermal elements become attached. The cavity of the heart is imperfectly divided by lateral
partitions into three longitudinal compartments. In Fig. 186 the partitions are imperfect and
represented on each side by a single rudimentary muscle fiber. The walls and partitions of the
heart are composed of delicate muscle fibers, which are distinctly striated. In the abdominal
muscles, striations can also be made out.

STAGE XIJ.—THE FIRST LARVA.

We now reach the stage with which this paper began, the first larva of Alpheus saulcyi.
The histological structure of the zoéa in the species with a regular metamorphosis differs dnly in
minor particulars from the larva already described. The organs are all very much smaller, and
the cells are relatively larger and less compact. The mesenteron is about half filled with the
unaltered and unabsorbed food yolk. Wandering cells are almost entirely absent, and the endo-
dermal walls are nearly complete. The partition between the masticatory stomach and the midgut
is absorbed and communication between them is established.

The anterior and median lateral divisions of the midgut are present, but the posterior lateral
lobes are represented only by spaces not as yet walled in by endoderm. There is a slight dorsal
median fold of endodermal cells. In the larva of the same species three days’ old the posterior
lateral lobes are formed, but are very small.

Stace XIJI1—ALPHEUS TEN DAYS OLD.

in the first twenty-four hours the larva moults twice, but the histological changes in this
period are not of a very extensive character. The organs which experience the most rapid growth
are the gills (Pl. Lut, Fig. 195.). These have now acquired the folds or plates for increasing the
respiratory surface, and are more efficient as breathing organs.

The fibrous tissue of the brain is relatively greater in bulk, and the tracts of fibers are more
numerous and more complicated. The eye stalks are much shorter, and the optic ganglia and
anterior parts of the brain are drawn closer together.

Ina larva four days old (Pl. xx1, Fig. 3) the eyes are completely covered by the carapace.
The ganglia of the eye stalks and brain are intimately fused together. The nervous system and
all the tissues have undergone greater or less histological changes. These can be more conven-
iently considered in a still older larva.

The period of metamorphosis, strictly speaking, is passed in about twenty-four hours after
the time of hatching. The structure of an Alpheus ten days old, which had spent its entire life
in an aquarium will now be briefly considered. It is sexually immature and some of the organs,
like the “liver” and green gland, are less complicated, but otherwise the structure is essentially
that of the adult fori.

When we compare the brain of the first larva with that of the ten days old and the adult
fully grown form, we find the same parts present in all. In the last two the fibrous tissue is rela-
tively much greater in bulk, and differentiation of the fibers and fibrous tracts has advanced much
farther. The brain consists of the same fibrous masses surrounded with a thinner cortex of nerve
and ganglion cells.

S. Mis. 94-——27

—_— <a

418 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

The anterior or optic enlargement is continuous on each side with the ganglia of the eye stalks.
Tts two halves are united by transverse fibers. The lateral enlargement is markedly kidney-shaped,
and from its hilus there issues a complex system of fibers. A great part of these fibers issue from
the ganglion cells inclosing the lateral ball, pass out in a bundle to the middle of the brain,
and thence up to the optic ganglia, apparently without crossing. The fibrous substance of the
lateral enlargement has a pyramidal structure—that is, its tissue is permeated with pyramidal blocks
of a denser substance which stains faintly with carmine. The apices of these pyramids point
toward the center of the ball. Below the lateral enlargement and nearer the middle line there is
the antennular mass from which the auditory nerve issues. This is bilobed and has the same gen-
eral relations as in the first larva (Pl. Lv, Fig. 216, If). The antennal enlargement, which is
closely connected with the latter, is now a much more conspicuous mass than in the earlier stage.
From it issue the antennal nerve and the esophageal commissures. Zs

The alimentary tract has undergone very important changes, of which mention was made in
Section 1. What corresponds to the foregut of the larva comprises that portion of the tract from
the mouth to the duct of the gastric glands. It is divisible into a straight and vertical portion,
the esophagus proper and a masticatory stomach. The latter consists of two parts, an anterior
section continuous with the cesophagus, and probably corresponding with the gastric will,
and a pyloric portion or strainer. In transverse section the cardiac section appears circu-
lar and the walls are rather thin and slightly folded. As this passes into the pyloric division the floor
of the tract rises into a broad tongue-shaped process, which is surmounted by a particular strainer
_ of hairs. This median fold is continuous throughout the pyloric division, where it narrows into a
crest.” The lateral walls, which are greatly thickened and studded with hairs, approach each other

so that only a small lumen is left, through which the food is strained as it passes over the net--

work of hairs. These two sections of the stomach correspond to portions of the tract marked Ws.,
Fig. 196. They are of epiblastic origin, and in passing to the midgut the epithelium suddenly
changes as it does in the larva.

The ducts of the three glands unite on each side and thus form two common ducts. The
epithelia of the gastric ceca of the ducts and midgut are directly continuous and pass gradually
into each other. They consist of a delicate layer of connective tissue which forms a capsular in-
vestment and the large columnar cells already described. In the “liver” many of these cells are
in the process of active secretion, and as a result of this activity the lumen of the gland is filled
with a coagulated liquid. The secreting cell at this period swells out to two or three times its
former size and has the form of a distended bladder projecting into the cavity of the gland. The
contents of the cell consist of a light granular fluid and when the cell breaks down this is dis-
charged into the lumen of the gland.

Just how much of the wall of the alimentary tract behind the glandular ducts is of endoder-
mic origin it is impossible to say, since from the first there is no sharp morphological boundary
betwéen the hindgut and mesenterou. But it is certain that only a very small portion of it can
arise in this way, and that the endoderm of the larva goes mainly, if not exclusively, to form the
lining of the gastric cea.

The heart is very much compressed from above downward as in the Sani. The walls of blood
vessels consist of a single layer of cells which secrete a homogeneous limiting membrane. As
in the early larva, the heart and pericardium are screened from the digestive tract and other organs
by a horizontal membrane. The reproductive organs are still in the rudimentary condition
already described.

V.—NOTES ON THE SEGMENTATION OF CRUSTACEA.*

Under this head I will add a few notes upon the segmentation of the egg of a number of
Deeapods, which have been studied chiefly for the sake of comparison with Alpheus.

Alpheus sauleyi and A. heterochelis are both typical examples of centrolecithal segmentation
with the ee of yolk pyramids. They possess a massive food yolk and hatch as mysis-like

* The Parana sections of this memoir were written after the lapse of a long interval, during which time it was’
not possible to refer to my earlier manuscript. This will account for any unnecessary reiteration of facts, or. for any
inconsistencies in statement which I haye failed to eliminate.

ea

a

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ALY

larve. On the other hand, the Bahaman variety of Alpheus heterochelis and Alpheus minor (from
Beaufort, North Carolina) agree in having a relatively smaller yolk and in hatching as zcea-like
forms. They differ, however, in their segmentation, the first species agreeing in this respect with
A. sauleyi, while in A. minor yolk pyramids are generally absent and the segmentation is irregular.
The yolk in A. heterochelis of Beaufort is about nine times as voluminous as that of the Bahaman
heterochelis. The segmentation, however, has remained unaltered. The peculiarities which we
tind in the early stages of A. minor can not therefore be laid to the door of the yolk alone, but must
be regarded as a comparatively recent modification of the yolk pyramid type. While the type of
segmentation may be very persistent and uniform, it is subject to profound change, not only in
closely allied species, but, as has been shown in a few instances, within the species itself.

In the Decapod egg we have, as a result of segmentation, a great central yolk-mass which is
either undivided or imperfectly divided, and which completely fills and obliterates the segmenta-
tion cavity, and a surrounding layer of tells, the blastoderm. More fully stated the process is as
follows: The segmentation nucleus divides first at a point near the center of theegg. The daugh-
ter cells separate widely, and a second division follows. With subsequent divisions the cells
approach nearer the surface. The yolk may share in these early divisions but often does not, until
eight or sixteen cells are formed (third or fourth segmentation stage). When there is no pro-
gressive segmentation of the yolk in the early phases, the yolk segments appear either gradually
and on one side of the egg, or make their appearance simultaneously in relation to all the nuclei
present. Segmentation is always rythmical. During oue phase (period of ‘“ rest”) the segnfents
shrink away from the surface and flatten out in the usual way, while at the beginning of the period
which follows (period of “ activity”) they swell and stand out prominently. The division of the
yolk often appears total in surface views, while in reality it is not. The constrictions marking
off the segments may be nearly superficial, or they may extend deep into the yolk. Cell division
is usually indirect. The only exception to this rule which I have observed is Alpheus minor (see
p- 397). With each division the protoplasm approaches nearer the surface of the egg, and the
segments become more pyramidal in shape. These are the “yolk pyramids” which were first
deseribed in the craytish by Rathke in 1829. The bases of the pyramids form the surface of the
egg and their apices fuse in the central yolk mass. The nucleus, surrounded by a rayed body of
protoplasm, lies near the base. By repeated division the pyramids become smaller; the cleavage
planes of adjoining segments become less distinct and the protoplasm draws nearer and nearer the
surface. Before, however, any of the protoplasm is flush with the surface, certain of the cells
divide horizontally, that is delaminate, and one of the products of each division migrates into the
yolk below. The surface of the egg is now covered with a single layer of small polygonal cells,
and the pyramidal structure of the peripheral yolk has nearly disappeared. The greater part
of the protoplasm of the egg is thus at the extreme outer encs of the reduced yolk pyramids, while
the lesser body of it is represented by the migrating yolk cells.

The invagination stage soon follows, and the large numbers of cells which now become migra-
tory (in Alpheus penetrating to all parts of the egg), joining the primary yolk cells, represent
mésoblast and entoblast. The process above described will be found to apply, I believe, to the
majority, if not to all Decapods. Differences in detail may be expected in the time of appearance
of yolk segmentation and the degree to which this is carried. This account differs from that usually
given in recognizing delamination, following close upon the latter phases of segmentation, or the
origin of cells, from the blastosphere before the invagination appears. This regularly occurring in
such typical forms as Alpheus and Homarus argues strongly for its presence in allied species
where it has possibly been overlooked.

Stenopus hispidus.—I have described and figured the segmentation of Stenopus in a paper on the
life history of this form. In one egg which I sectioned before the beginning of yolk segmentation, a
single cell, probably the male pronucleus, is seen at the surface, while another cell, the female pro-
nucleus, lies near the center. A single polar body was also present, just beneath the shell, near
the first nuclens. I saw no evidence of yolk segmentation until the third phase of division was
reached. The yolk then became constricted at the surface into eight blastomeres. The superficial
furrows are quite deep during active periods, giving to the egg the appearance of total cleavage.
This egg now resembles that of Peneus as figured by Haeckel, butin the latter form yolk segments

. MEN, we <:
420 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

appear at an earlier phase. The cleavage of the yolk is wholly, or almost wholly, confined to the
surface furrows, dividing planes rarely extending into the yolk below. My material was not ade-
quate for determining whether invagination was preceded by delamination or not, but seems to
render it highly probable that a delamination does not occur. ;

My observations on Pontonia domestica, Palemonetes vulgaris, and Hippa talpoides are very
fragmentary. In Pontonia I have one stage (Fig. 27) with three cells, one of which is dividing
with no sign of yolk division, and another with sixteen nuclei and corresponding yolk
pyramids. Here the conditions are precisely like those in Alpheus saulcyi at a similar stage,
and probably the segmentation of the two is similiar. In Palemonetes Faxon (17), relying
wholly upon surface views, states that segmentation of the egg begins in two planes_almost
simuitaneously. These planes are at right angles to each other and pass through the long and
short axes of the egg. Whether this follows close upon the first division of the nucleus I have
not determined. I have an egg with two naclei near the center of the undivided yolk, and a stage
with thirty-two yolk pyramids. This egg also agrees closely with that of Alpheus saulcyi at the
same stage. The nuclei are not quite at the extreme surface of the yolk. In the next phase when
sixty-four pyramids are present the protoplasm abuts on the surface (Fig. 24) of the egg. All the
protoplasm is distributed to the yolk pyramids and no delamination has taken place.

With reference to Hippa I can only add the note that yolk pyramids normally occur, and in
the 64-cell stage (Figs. 1, 4) the lines of cleavage between adjacent segments are very distinct and
extend nearly to the center of the egg. At this stage all the proteplasm is apparently concen-
trated in these cells. Yolk pyramids similar in surface views to those of Hippa occur in Callinectes
hastatus, Platyonychus ocellatus, and Libinia canaliculata.

Orangon vulgaris.—Kingsley (31) describes the segmentation of Crangon as follows:

With the first segmentation the protoplasm begins to leave its central position and seek the surface of the ogg;
before the second division is completed it has reached the surface, leaving the yolk in the center. * * * After the
second protoplasmic segmentation is effected the first segmentation furrows appear, the one following close upon the
other. The iirst to appear corresponds in its direction to the first nuclear division; the second is at right angles to

it. * * * In Crangon, so far as I have been able to see, amceboid cells reach the surface and take part in the
formation of the blastoderm before the process of gastrulation begins. In that form no yolk pyramids occur.

Of cell division he says:

In the process of cell division I have never seen any traces of karyokinesis; the division seems to be direct; and
affects first the nucleus and next the protoplasm. * * * In fact I do not recall a single statement of karyokinesis
being witnessed in decapod segmentation excepting in Astacus.

On Pl. 1 he gives a drawing (Fig. 3) of an egg with “about sixteen segmentation spheres.”
Fig. 4 of the same plate represents a section of the egg shown in Fig. 3 and has six nuclei, five of.
which are even with the surface, while one is near the center of the egg. The yolk spherules appear
to be fused, owing possibly to the disturbing effect of the reagents employed. This central cell,
according to Kingsley, represents a portion of the egg protoplasm which is belated in its passage
to the surface, but it divides and gives rise to cells which eventually reach the surface at a certain
point which marks the germinal area. Thus all the nuclei take part in the formation of the blasto-
derm, and the migration of the belated cells is completed before the “gastrula” invagination
occurs. [have made no observations on the very earliest phases of segmentation of Crangon, but I
have several eggs sectioned at the sixteen-cell stage, which ought therefore to correspond with
Fig. 4 of Kingsley’s paper, but, on the contrary, they show a somewhat different condition of
things. There are just sixteen nuclei present, all of which are peripheral or nearly so, and each
nucleus forms the center of a yolk pyramid, the cleavage planes of which are very marked and
extend more than half way to the center of the egg. Fig. 15, Pl. xxvu, of the segmented egg of
Alpheus, although belonging to a later phase, will fairly represent the condition of things which
we find in Crangon. None of the nuclei are tangent to the surface, but between them and the sur-
face there is still a considerable layer of yolk. Each is surrounded by a large mass of protoplasm,
which stains lightly with hemotoxylon, and has the characteristic rayed appearance. One of these
uuclei is in the equatorial plate or metakinetic stage of division, and may be represented very
nearly by Fig. 28, which shows a dividing cell in the egg of Alpheus at the same period. Asaiready
stated, the central yolk mass does not contain a single nucleus. The yolk is in the usual form of

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 421

large spherules on angular blocks, which are abundantly perforated with round lacunz. Crangon
agrees essentially at this stage with at least three other species, namely, with Alpheus sauleyi,
Pontonia domestica, and Stenopus hispidus.

It is probable that Figs. 3 and 4 of Kingsley’s paper do not correspond, the latter representing
the older egg, that is, older than the sixteen-cell stage. In the segmenting eggs of Homarus there
is a striking individual variation, which finds expression chiefly in the external characters of seg-
mentation, but I have never observed this in any related forms, and can not say to what extent it
oceurs. Judging from analogy, I think it will be found that as a rule all the protoplasm in the egg
of Crangon vulgaris reaches, or very nearly reaches, the surface, as in Homarus and Alpheus saulcyi,
and that toward the close of the yolk-pyramid stage delamination occurs and some of it wanders
back into the depths of the yolk. If this is true, the “belated” cell near the center of Fig. 4 of
Kingsley’s paper may represent some of the protoplasm which has taken this ronndabout journey.

{While this memoir was in press a paper has appeared by W. F. R. Weldon, on “The Forma-
tion of the Germ-layers in Crangon vulgaris.” (Quart. Jour. Mic. Sci., Vol. xxxut, pt. 3, March,
1892). He makes no mention of the budding of cells from the blastoderm before invagination,
nor of the presence of migrating cells at a later period not derived from the invaginate cells or
ventral plate, hence it is probable that in Crangon primary yolk cells do not occur. In this case
the suggestion just offered does not let us out of the difficulty.] I have not succeeded in obtaining
the segmenting eggs of Callianassa for comparison with the early stages of Callianassa mediterranea,
described by Mereschkowski (40). It seems to me, however, that the diagrams in Mereschkow-
ski’s paper are misleading, and that the process of segmentation in Callianassa, instead of being
peculiar as one might infer, is essentially typical. According to this observer's account the ‘“ blas-
toderm” arises without yolk segmentation. Nuclear division is at first central, and the resulting
cells, sixteen in number, pass gradually to the surface and form a deep layer of protoplasm
inclosing the yolk. This layer, at first raised into hillocks corresponding to the nuclei, finally seg-
ments into sixteen parts around the latter. These segments are formed simultaneously over the
egg, but the yolk is not involved. The cells multiply rapidly and form a layer of tall prismatic
elements, which gradually flatten out as division proceeds, into ordinary blastoderm cells.

If there is any analogy between this egg and that of related forms the broad “ protoplasmic”
layer is really the protoplasm plus the peripheral yolk. It would be remarkable in any case if
a segmenting egg could acquire such a mass of protoplasm, not to speak of the suddenness with
which the acquisition is made. That this layer, comprising more than one-half the contents of the
egg, is largely yolk is indicated by the fact that the nuclei which occur in it are represented as
surrounded by a protoplasmic reticulum as normally oceurs. If this is true, the prismatic cells are
yolk pyramids, and their line of separation from the central yolk is purely imaginary.

Ishikawa found, in his studies upon a Japanese prawn, Atyephyra compressa (27), that the egg
underwent at first a total and regular segmentation. At the end of the fourth phase the yolk is
centralized and the protoplasm surrounds it, and in the next stage, after thirty-two blastomeres
have been formed, the central end of each separates off to form a yolk segment. The yolk seg-
ments, which fill the center of the egg and correspond to the common yolk mass with which the
apices of the yolk pyramids blend in other Decapods, are of unequal size and contain nuclei which
do not take part in the “blastoderm.” These nuclei probably correspond to the delaminated cells
of Homarus and Alpheus. In the latter they appear at the close of segmentation. It is quite
probable that the time at which these cells are budded off may vary considerably in different
species.

‘In Eupagurus prideauxii (39) Mayer found that the protoplasm segmented first in the center
of the egg, as in other forms, until eight nuclei were present. When this stage is reached the yolk
now segments not simultaneously into eight blastomeres, as in the case with the Isopod Asellus
aquaticus, but according to its inherited primitive manner, first into two, then into four and eight

_spherules. Segmentation of the yolk is thus at first total, but after the fourth phase the spheres
unite in a central yolk core as in other forms.

In Alpheus sauleyi I did not find any eggs which showed a progressive segmentation of the
yolk between the stages represented in Figs. 9 and 10, and hence I infer, as already stated, that
the segmentation of the yolk is there a simultaneous process for each of the sixteen segments

422 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

involved. This remark also applies to Stenopus, where eight blastomeres or yolk pyramids appear
at the beginniug of the third phase. In Homarus there is less uniformity in the appearance of the
superficial segments, since the cells do not migrate to all parts of the surface at a uniform rate.

Lereboullet (36) described the early stages of the segmenting egg of the crayfish Astacus
fluviatilis in 1862. His account, though somewhat vague and unsatisfactory owing to the tech-
nical difficulties under which he labored, is confirmed in essential particulars by a later observer,
Skimkewitch (56), who has given a short description, without figures, of the process in the Russian
crayfish Astacus leptodactylus. His account is briefly as follows: The cleavage nucleus with its
protoplasm passes from the center to the surface of the egg and undergoes segmentation. The
resulting nuclei, the exact number of which is not given, then diffuse over the surface of the egg
and the yolk eeore around them. The cleavage planes between adjacent pyramids, at first
extend only half way to the center of the egg and never quite reach it. There remains at the close
of the segmentation a small mass of undivided yolk (“‘ dotterkern”) lying in the center of the ovum.

According to these observations then, Astacus offers us an example of centrolecithal segmen-
tation in the most exact sense of the term. It seems to me quite probable that this migration of
the protoplasm may be only apparent, and that the segmentation may proceed much as it does in
the lobster.

Brooks, in his memoir on Lucifer (8), gives an account of a segmentation which differs in
some particulars from that of any macrouran which has been studied. The Lucifer egg undergoes a
total and perfectly regular segmentation, and in the first stages may be compared with Eupagurus.
In Lucifer, however, a segmentation cavity is formed, which can be clearly seen when sixteen
spherules are present. At this time one pole of the egg becomes flattened, and one of the spherules
in the area, which has become differentiated by the possession of food yolk, is gradually invagi-
nated into the segmentation cavity. Meantime the invaginated cel) divides; other changes ensue

which lead to the infolding of more cells and the formation of a two-layered embryo, the “ gastrula.” .

Brooks thinks that ths yolk. bearing cell represents a yolk pyramid, and that after a longitudinal

division each half divides transversely or delaminates, and that the other two inner cells contain the:

yolk, while the outer products remain at the surface and form a part of the “blastoderm” (or endo-
dermic invagination). This last point, however, was not settled. In Brooks’s view the segmenta-
tion in Lucifer is a secondary modification of the yolk pyramid type, and this has been brought about
““by the gradual reduction of the amount of food material and its restriction, at last, to a single
one of the cells of the segmenting egg.” He says that, while Lucifer is undoubtedly a very primi-

tive Malacostracan, it can hardly be regarded as a primitive Crustacean; and since we meet with

abundant examples of centrolecithal segmentation both above and below Lucifer, we can not regard
the Lucifer egg as ancestral or as the unmodified descendant of an ancestral type of egg. “We
must, therefore, believe that the egg of Lucifer has been simplified by the loss of the greater part
of its food yolk.”

It is to be regretted that Professor Brooks did not find material sufficiently abundant to war-
rant the sacrifice of some of the segmenting eggs for sections; for until this is done we can not be
certain of the origin and relations of the mesoblast and entoblast in this extremely interesting
species. A careful study of the subject both in Lucifer and Sergestes would form a very valuable
and much needed contribution.*

It seems to me quite probable that we have in Lucifer a repetition of what occurs in Homarus
and Alpheus, and that the yolk-bearing cell corresponds to the inwandering or delaminated cells,
which ocenr in the lobster at the close of segmentation. In each case they arise by transverse
division from the superficial cells of the blastophere. In each case, also, they appear just before
invagination, and migrate into the segmentation cavity. The differences are that in the lobster,
for instance, the segmentation cavity is already filled with yolk ; the centripetal cells are numerous,
and they do not necessarily come from that point on the surface which corresponds to the point
of invagination or ingrowth. As to the comparative history of the two cells in the two cases little

* Since ee was Derrikton Professor Tees has announced in his report of the work of the marine laboratory of
the Johus Hopkins University, that he has recently obtained the eggs of Lucifer in abundance at Jamaica, and is now
engaged in studying its embryology. «

*

ee, . ya

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 423

ean be said. Brooks thought that in Lucifer they represented the food yolk, although this was
not settled. In Alpheus these cells are later joined by great numbers of wandering cells at the
invagination period, and out of this common stock, so far as we can determine, both mesoblastic
and entoblastic organs are developed. In Homarus, on the other hand, the invaginate cells
unquestionably degenerate.

The eggs of Scyllarus and Palinurus have not been thoroughly studied, so far as I am aware.
Dorhn (14), however, has figured the eggs of Scyllarus arctus in late stages of yolk segmentation,
and in surface view they resemble, at this time, the ordinary Decapod type. We have as yet no
knowledge of the segmentation of the Stomatopods.

The relations of the different varieties of segmentation which are met with among the Deca-
pods, may be expressed by the following table:

(1). Lucifer typus.

I. Total: regular: seg-
mentation cavity pres-
ent.

(1) Palemon. .

(2) Bupagurus prideauii.
(3) Atyephyra compressa.
3 Peneus.

Segmentation of the } © Segmentation of yolk at first to- §
Decapod egg. tal, afterwards partial.

(2) Crangon.

IL. Partial: centroleci- (3) Stenopus hispidus.

thal (yolk pyramids):
segmentation cavity
filled with yolk.

(4) Alpheus saulcyi.
( Regular. (5) Pentoais domestica.
(6) Hippa talpoides.
(7) Palamonetes vulgaris.
(8) Callianassa mediterranea.
(1) Homarus americanus (yolk
segmentation at first ir-
Urregular regular, but later regular
or nearly so).
(2) Alpheus minor.

Lan. Segmentation cal
yolk. 4

———,

~ Of the Thoracostraca, the Schizopods undoubtedly depart widest from the common decapodal

type of segmentation. Nusbaum (45) thus describes the process in Mysis OChameleo: The -pro-
toplasm—that is, the segmentation nucleus, with its protoplasmic body—retreats to a point at the
surface of the egg. The nucleus then suffers division, and the protoplasm becomes differentiated
into an outer striated zove containing a single nucleus, and an inner granular zone with one or more
nuclei. The single external necleus divides and gives rise to a small blastodermic disk, formed of
a single layer of hexagonal cells. Krom the internal nuclei and protoplasm a small number of nuclei
are produced under the blastodermic disk. The free cells below the disk are the products (1) of
the nuclei and formative protoplasm of the deeper layer, and (2) of the cells of the upper layer or
blastodermic disk. While a solid accumulation of cells is thus being formed below the disk, the
superficial cells gradually extend on all sides and inclose the egg. The thickened disk marks the
ventral side of the embryo. It divides into a median, caudal, or abdominal plate, and two lateral
plates, the ventral bands. Yolk cells which were not present up to this stage, now arise by migra-
tion from the abdominal plate.

The segmentation of the Schizopod is especially interesting, since it agrees so closely with that
described in certain Isopods and Myriapods, and resembles also the segmentation of Arachnids.

Bobretyky’s observations on Oniscus (5) need to be repeated, and especially in the early
stages. According to this observer the earliest phase of segmentation was characterized by the
anomalous withdrawal of the egg protoplasm to the surface, where it accumulated in a distinct
body, and underwent segmentation. A disk of large columnar cells was thus formed, marking the
ventral surface of the embryo. The cells spread with the thickening of the disk, until they inclose
the entire egg. The superficial cells form ectoblast, the rest entoblast and mesoblast.

Morgan (41) has described a form of segmentation in Pycnogonids which resembles that of the
Decapod. Here the invagination (which leads to the formation of the stomodeum) is preceded by
the delamination of endoderm cells from the blastosphere, very much as in Alpheus, if we may
regard the yolk cells as primitive endoderm.

424 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

In Agelena, Locy (37) found the unsegmented egg to contain a central nucleus and protoplasm,
united by a fine network to a peripheral protoplasmic layer, the blastema. The nucleus divides,
and its products pass gradually into the blastema, which is used up in forming the blastoderm. ;

3ruce (10) speaking first of Bobretyky’s work, thus describes the formation of the blastoderm —
in Lepidoptera:

In the earliest stages he found four ameebiform cells in the yolk, situated in pairs at opposite ends of the egg.
Later the blastoderm is formed by a multiplication of these cells ; according to Bobretyky it is not formed simultaneously
over the entire surface of the egg. but is laid down first at one or more points on the surface. This type of segmenta-
tion can not strictly be called entolecithal, inasmuch as the cells are not, in the earliest stages of segmentation, at
the surface inclosing the yolk. All the primitive undifferentiated cells do not, according to Bobretyky, reach the
surface to form the blastoderm, but some remain centrally located as yolk cells after the formation of the blastoderm.
The earliest stages of segmentation observed in Thyridopteryx showed several amcebiform cells in the yolk in each
cross section. ‘

In Thyridopteryx the blastoderm is first formed in a given area on the surface, afterward com-
pletely inclosing the egg, but in this particular closely related insects seem to differ.

Heider’s recent observations on Hydrophilus (24) show that numerous nuclei which originate
from segmentation, do not reach the surface to enter into the ‘‘ Keimhautblastem,” but remain in
the yolk as yolk cells. :

The segmenting egg of Julus terrestris is described by Heathcote (19) as a syncytium. Seg-
mentation is at first central, and the resulting nuclei are united by strands of protoplasm. Upon
reaching the surface they spread themselves over it to form a blastoderm. The blastodermie cells
are united to each other by strings of protoplasm, and to the cells of the yolk. The entire egg is
thus pervaded by a network of protoplasm. The yolk cells are regarded as entoblast, and give
rise to the “keel” or thickened blastodermic plate. This stage, characterized by a thickened
blastodermic disk, keel, or cumulus, probably corresponds to a similar stage which is met with in
Schizopods, Isopods, Myriapods, to the primitive cumulus in Arachnids and the ventral plate
which suffers invagination in some insects. Possibly it corresponds also to the invagination plus
the thickened ventral plate of Alpheus and Homarus.

Possibly we have in Astacus and Homarus an approach to the mesoblastic type of segmenta-
tion, such as is found in Mysis. This would be reached in Astacus if the protoplasm (which accord:
ing Skimkewitch passes at once to the surface) should in the course of division build up a disk,
instead of diffusing itself over the egg. A similar result would be achieved in Homarus if the
belated cells should not reach the surface at all, and if those which are first to appear should not
ditfuse over the egg, but segment to form a thickened plate.

Balfour says, in speaking of forms like Penzus:

It is probable that not all the nuclei which result from the division of the first segmentation nucleus become con-_
cerned in the formation of the superficial blastoderm, but that some remain in the interior of the ovum to become the
nuclei of the yolk spheres.—(Comp. Embryology, Vol. t, p. 113.) ks

This, I think, is an error, and that what is true of a number of forms, as Alpheus, Crangon,
Homarus, probably expresses the rule for the Decapods, that all the egg protoplasm enters into
the peripheral cell layer. Exceptions to the rule may, however, occur.

The use of the term centrolecithal to express the relations of the protoplasm and the yolk in
the egg of Arthropods is not beyond criticism, but the strict application of a single term is clearly
impossible. The ground of any objection is sufficiently covered by Balfour, in emphasizing the
fact that it is the centrolecithal condition which is eventually attained. He says:

As might be anticipated on the analogy of the types already described, the concentration of the food yolk at the
centre of the ovum does not always take place before segmentation, but is sometimes deferred till even the later stages
of this process.—(Comp. Embryology, Vol. 1, p. 110.)

In most cases the protoplasmic segmentation is at first central, or, as Kingsley points out,
ectolecithal, and then, after passing through the intermediate stage, it is finally centrolecithal.

The question as to whether the products of the segmentation nucleus before the yolk is
involved, are to be regarded as independent cells was raised by Balfour, who, in reference to
Bobretyky’s work on the embryology of inseets,.says:

He regards the nuclei surrounded by protoplasm, which are produced by the primitive segmentation nucleus, as
80 many distinct cells. These cells are supposed to move about freely in the yolk, which acts as a kind of intercel-

°

‘ *

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 425

lular medium. This view cape not commend itself to me. It is opposed to my own observations on similar nuclei
in the Spiders. It does not fit in with our knowledge of the nature of the ovum, and can not be reconciled with the
segmentation of such types as Spiders, or even Enpagurus, with which the segmentation in insects is undoubtedly
closely related.—( Comp. Embryology, Vol.1, p. 119. )

This discussion seems to have arisen from a confusion of the morphological and physiological
significance of the cell. The segmentation of the nucleus and its surrounding protoplasm is plainly
the only important phenomenon, and the segmentatior of the yolk is not merely asecondary process,
but in many cases a wholly unnecessary one, as we see in the early phases of many Decapods.
In these cases the individuality of the yolk pyramid is temporarily sacrificed’or subordinated to
that of the true cell, which is surrounded by unsegmented yolk. Later, when the yolk has become
divided, the yolk segment or pyramid is gradually reduced until we get the superficial, embryonic
cell, with more or less definite boundaries. All the elements of the egg, whether superficial or
amceboid, are clearly to be regarded as cells in a fundamental, physiological sense, as shown by
the part which they play in the development of the embryo.

SECONDARY SEGMENTATION OF THE YOLK.

There are traces of a secondary segmentation of the yolk in Alpheus during the second, third,
and fourth stages; that is, from the period of invagination to the outlining of the primary append-
ages. The yolk spheres arrange themselves in spherical clusters or balls, so characteristic of the
early development of nearly all the Arthropods. The yolk ball contains at least one yolk nucleus

with perinuclear protoplasm and corresponds to a yolk pyramid, being a cell in the same sense as.

the latter. Various phases of this secondary segmentation may be seen by glancing over Pls. xxx-
xxxv_ In one egg, which I sectioned just prior to invagination (Fig. 46), there appears a segmen-
tation of the yolk around the central nuclei.

Bobretzky attributes a morphological value to the secondary segmentation of the yolk in
Arthropods, supposing it to be connected with the spreading and final establishment of the ento-
blast. The secondary yolk pyramids or giant endoderm cells, which form the lining of the midgut
of the embryo crayfish, he compared with the Dotterballen of Oniscus and Palemon. In Palemon
the food yolk breaks up into round or polygonal pieces soon after the blastoderm is formed, while
in Oniscus certain cells pass into the yolk from the keel or germinal eminence and gorge them-
selves with the yolk substance until they form large balls, which represent the endoderm (Darm-
driisenzellen). It is stated, however, by Nusbaum (44) that a part of the endoderm of Oniscus
which gives rise to the gastric gland arises from primitive mesoblast, and in insects the endoderm
is formed independently of the yolk cells. The history of the yolk cells and of the wandering cells
will be discussed in another section.

VI.—CELL DEGENERATION.

The rapid and often extensive breaking up and final disappearance of embryonic cells in the
course of Arthropod development is a very remarkable phenomenon, and strange to say, it has
almost escaped attention up to the present time among the Decapod Crustacea. A study of this
subject in Alpheus, Astacus, and Homarus has convinced me that the peculiar bodies described
as secondary mesoderm cells in the crayfish (54) correspond to the degenerating, sporelike par-
ticles which characterize similar stages in the development of both Alpheus and Homarus.

In some early notes on the development of Alpheus I called these nuclear fragments “spores”
(22), but the term is inappropriate if we are dealing with cells in the process of dissolution, as is
undoubtedly the case. The anomalous “secondary cells,” which have been a sort of outstanding
puzzle to embryologists, receiye, in my opinion, a more reasonable explanation on the ground that
they represent degenerating elements. This view is supported by a comparative study of embry-
onie growth in other Arthropods.

Alpheus.—Degenerating cells are present in Alpheus saulcyi in considerable numbers when the
nauplius appendages are budding and increase for a short time beyond this period. They continue
in greater or less quantity until six to eight pairs of postoral appendages are formed, when they
disappear from the embryo almost completely. They vary in size from small refringent particles
to spherical masses as large as ordinary nuclei, or even larger. Many nuclei, instead of having
the normal appearance, in which the chromatin has the form of a coil or a reticulum with stellate

eb ee

TY

426 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. — Ayr ae!
nodules in its meshes, begin to show retrogressive tendencies. They sometimes appear swollen out
to an unusual size, and their chromatin is aggregated into a single large ball, which may become
vesicular and strongly refractive. The chromatin ball is sometimes of large size, central in posi-
tion, and stained intensely, suggesting strongly the nucleus of a blood cell, or it may stain so
faintly as to be hardly recognizable. Again, it may be eccentric and attended by one or more
smaller balls, or the nuclear body may be filled with numerous coarse grains. These bodies then
recall yeast cells in process of producing ascospores. As in the yeast cell, the wall of the
nuclear body seems in many cases to break down and thus set free into the yolk the naked, spore-
like masses of degenerating chromatin.

In Figs. 21 and 32 (Pls. XX vU, xxrx), taken from the egg-nauplius embryo,we see various stages
of this process. Around the stomodzum, and within or near the pockets of the antennz and mandi-
bles, there are large numbers of these pseudo-spores. Some are small chromatin balls (8), which
combine actively with hemotoxylon, while others stain feebly or are quite unaffected by the dye,
and resemble straw-colored particles of vesiculated and altered food yolk. Below and to either
side of the stomodeum there is a granular residue (Fig. 118, A. Y.S.), composed of you and nuclear

matter in various stages of chemical degeneration.

The ordinary nucleus in the resting condition is generally characterized by the presence of
balls, nodules, or granules of various sizes, which represent chromatin constituents of the nucleus.
Under high powers these usually appear as stellate masses suspended in the nuclear reticulum.
A number of representative nuclei are shown in Fig. 18. They are all drawn to scale and are
taken from the egg-nauplius series under review. It is so plain that it is hardly necessary to state
it, that the nuclear fragments in these bodies, e, f, or h for instance, correspond to similar fragments
which occur free in the yolk. The larger nedule in the nucleus f resembles figure b, except that
the latter is surrounded by an outer light zone. This zone is often very large and not as sharply
defined as in the drawing. Again, figure ¢ resembles figure ), except that the outer light zone is
larger in c and the chromatin or stainable residue has nearly disappeared. I regard the bodies )
and ¢ as masses of degenerating chromatin which have escaped from a disrupted nucleus or cell.
In ¢ the retrogressive changes are furthest advanced. Finally, when the chromatin or stainable —
matter has been completely disorganized, there is left a vesiculated mass which stains very feebly
or not at all, and resembles yolk (Figs. 102, 107, A. Y.S.). Nearly every drawing of the egg-
nauplius stage shows one or more bodies Sian bin Fig. 18 (see Fig. 21, s,s’, and Fig. 32, s').
In many cases the outer light zone is cloudy, as already stated, and the element resembles a spherule
of yolk with a ball of chromatin imprisoned in it. These bodies bear a certain resemblance to
blood cells, but this resemblance is probably transitory, and after a careful study of a great many
stages I can find no direct evidence that they are ever reorganized into new tissue. The blood
cell of the adult is shown in Fig. 19 and that of an embryo in Fig. 35. In each case it consists of
a deeply staining granular nucleus and a clear cell body. The nucleus corresponds to the
apparently naked yolk nucleus (Fig. 35, Mes.; Fig. 18, etc.) and the cell body to the perinuclear
protoplasm, which is present, though often of small quantity, in the wandering cells. As we have —
already shown, it is probable that the blood cell (Fig. 35, B. C.) is derived directly from the wan-_
dering cell (Mes.), and that the characteristic appearance of the cell protoplasm is a rapid acquisi-
tion.

Degenerating nuclei may be seen by glancing over the plates (PIs. XXXVII-XXXIX and XLI-XLIV),
but it is unnecessary to refer to these in detail.

The dorsal plate or dorsal organ(?) furnishes a most striking instance of the degeneration of
cells (Pl. xxrx, Fig. 36; Pl. xvi, Fig. 153). Its cells seem to originate from the ectoblast, with
accessions possibly from the wandering cells. After the slight ingrowth, which takes place in the
middle of the plate, many of the cells pass into the depths of the egg and break up into meteoric
clouds of small deeply staining particles.

To sum up the previous remarks which relate to the appearance of these bodies in Alpheus, |
degenerating cells are first seen in Stage Iv, and in the following egg-nauplius stage they are
abundant. In Stage vil (Pl. xLrv, Fig. 131) they are still present, and in Stage vim there is a
fresh irruption of degenerating products into the yolk, arising from the centripetal cells of the
dorsal plate. Ata slightly later period they have almost wholly disappeared. Even as lateas
in the tenth stage a few chromatin granules can be seen in the region of the dorsal plate. :

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 427

CELL DEGENERATION AND AMITOSIS IN ALPHEUS MINOR.

In the segmentation of Alpheus minor there are numerous cases which illustrate the fragmen-
tation and apparent degeneration of nuclei. A nuclear body sometimes seems to be breaking down
and discharging a large number of sporelike balls or grains of chromatin (Fig. 26, Pl. xxvin, 8. C.).
This probably represents an element in process of dissolution. If this be true, the clear area is
similar to the plasmalike mass shown in Fig. 13, in which the nuclear bodies have disappeared from
view. Clear areas are sometimes seen containing only minute particles of nearly dissolved chro-
matin. The large swollen bodies, like those shown in Fig. 23, each with a single, often minute,
ball of chromatin, certainly remind us of somewhat analogous structures which can be seen at a
later stage in the crayfish.

The egg sectioned in Fig. 12, Pl. xxv, contains eight large nuclear nests or shells. The
nuclear masses are seen to be very irregular in size, and in some instances the nuclei are unques-
tionably breaking down. In other cases the egg contains a smaller number of large, very irregular
masses of nuclear material, consisting of a fine network, with chromatin granules in suspension.
These nuclear masses sometimes appear to be constricting into two parts. The swarm of small
nuclei, like that shown in Fig. 13, I interpret, as already stated, as arising by a kind of budding of
the large nuclear mass and the subsequent constricting off of the buds.

It is very interesting to find that in this case, possibly the only case of amitotic cell division
in the segmentation of the ovum yet recorded, the indirect division of the nuclei is followed to
some extent by a degeneration of these bodies. This lends some weight to the view that indirect
division is connected with the senescence of nuclei.*

The nuclei of the large endoderm cells lining the mesenteron in the crayfish appear to divide
directly, and in this case the process is again followed by dissolution. In may, however, prove
that we have here a case of multiple karyokinesis, similar to that which I have recently observed
in the superficial cells of the lobster embryo, where nests containing from four to sixteen closely
packed nuclei are very characteristic of certain early stages.

CELL DEGENERATION IN ASTACUS AND HOMARUS.

Homarus americanus.—I find certain bodies'in the lobster essentially similar to those which
characterize the Alpheus embryo. If a longitudinal section of the egg nauplius of Homarus be
compared with Fig. 125, which represents a similar section of a similar stage of Alpheus saulcyi, we
find not a few chromatin balls, but a meteoric swarm of granulated bodies and naked chromatin
grains coextensive with the embryo, and reaching a considerable distance into the yolk amid the
scattered mesodermic cells, but perhaps most abundant, as in Alpheus, in the neighborhood of the
stomodeum. <A long nebulous train of yolk spherules and granules extends forward a consider-
able distance in front of the mouth, and is especially marked in front of the optic disks. The
labrum and the folds of the appendages which contain yolk abound in these peculiar granulated
bodies. In less number they oceur in connection with the endoderm cells, which have at this
stage extended through a greater portion of the egg and form a series of ee sacs filled with
yolk. These yolk masses, with their surroundifig sheet or advancing column of:cells, correspond
to the endoderm sac of the crayfish. In the latter the peculiar cell bodies also occur.

If one now examines very thin’ sections under high powers, we find that the granules and the
granulated bodies correspond in general to the structures we have found in Alpheus. The chroma-
tin grains appear sometimes as naked masses in the yolk; sometimes they possess a distinct proto-
plasmie body. The degenerating chromatin stains either very intensely or faintly and is often
vesiculated; that is, if appears as a hollow shell. Under favorable conditions it is easy to demon-
strate the fact that these bodies surround particles of yolk, and occasionally they have a crescentie
BADE: when it can be paeecn: seen es mbey are enwrapping a yolk spherule. This bgp eats

4 While this memoir was in press a paper was received on Amitosis in the Wiantirjaaiak Ruyelopea of the Saetniin: ie
H. P. Johnson, (Bulletin of the Museum of Comparative Zoélogy, Vol. xx, No.3). Only two instances of direct cell
division in the embryo of Arthropods are recorded: that found by Carnoy in the ventral plate of Hydrophilus piceus
and the case which Wheeler has described for the blastoderm of Blatta germanica. Mr. Johnson finds that degen-
eration does not always follow upon indirect cell division, as in the case of amitosis in the testicular cells of certain
Isopods,

428 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

>

characteristic is certainly not so apparent in Alpheus, yet I believe that in this form it is present
in some stages, though in a less marked degree.

Astacus (?)—I have studied several critical stages in the development of the crayfish, critical at
least so far as the appearance of degenerative products is concerned, with an eye to comparison
with Alpheus and Homarus.* The youngest set of embryos Coreen tiaa nearly to Reichenbach’s
stage E, but differs from it in some details. Rudiments of five pairs of appendages are present,
the two maxillw being seen between the mandibles and the thoracic-abdominal process. None
of the appendages, however, are folded. The mouth is seen on a line between the first and second
pair of antenne.

The bodies which Reichenbach ealls ‘“‘secondary mesoderm” oceur in ainndatieet in or near the
wall of the endoderm sae next the embryo. They also abound in the yolk under the ectoderm,
and are most numerous in the area extending from the optic invaginations to the mouth or slightly
bebind it. In thig respect they recall the distribution of similar bodies in Alpheus and Homarus.

I wish to call attention to the fact that at this stage none of my sections show a cavity in the
endoderm sac, as is represented by Reichenbach (compare Taf. vii, 54), and the endodermal yolk
segments or pyramids do not always possess completed walls. To what extent this appearance is
normal, and to what extent due to the action of reagents, I can not at present say. These eggs were
treated with hot water and corrosive sublimate. The endodermal nucleus is surrounded by a thin
layer of protoplasm, which works its way amid the yolk so as to practically surround a pyramidal
mass. This strongly recalls the serpentine manner in which the endoderm cells creep through the
yolk in Homarus. Whether these cells in Astacus are simply migrating in a column or sheet,
spreading gradually towards the periphery of the egg, as in the lobster, cannot be decided from the
material at my comntand, but it is a point of considerable interest in its morphological bearings,
The endodermal cells probably multiply indirectly, but I saw no nuclear figures in my sections,
and they appear also to divide directly, independently of the yolk pyramids as Reichenbach
has described, giving rise to the chromatin balls and granulated elements (compare Fig. 20) but,

as pointed out above, this appearance may be very deceitful. This process is most marked in the

endodermic area noticed above, underlying the anterior half of the embryo. Here we see great
numbers of the bodies of varying size, both within and without the domain of the endoderm cells.
They closely resemble the vitellophagous elements which I have described for the lobster, and
possibly they attack the yolk in a similar way. Where they are thickest the yolk is comminuted
and shows traces of profound chemical change. In the midst of the altered yolk one can discover
very faint outiines of vesicular bodies which exhibit but slight reaction to the stain. These I
regard as degenerated cells. Z

The next stage of Astacus which I have studied corresponds nearly to Reichenbach’s stage G.
Right pairs of appendages are present, and there are rudiments of a ninth pair. The first and
second maxille appear as distinct buds, while the third pair of maxillipeds is represented by a
proliferating cell area only. The extremity of the abdomen is not bifid.

In the central part of the endodermal sac there is a coagulable fluid which comes in close rela-
tion with the posterior end of the embryo. The gndodermal cells laterally have quite or nearly
reached the ectoderm, while dorsally they fall a little short of the surface. The yolk within the
confines of the endoderm has an irregular, pyramidal, or radjal cleavage. Centrally the yolk
blends with the serum-like fluid, in which occasional granules or balls of chromatin may be found.
Small spherical elements (like those represented in Fig. 18, a, b, ¢, or k, k,' Fig. 20), containing a
single chromatin ball or several balls, occur not only in the yolk underneath the ectoderm and in
the vicinity of the endodermal nuclei, but also in the central yolk of the endoderm sac, at various
levels below the endodermal nuclei. This is a point of some interest in connection with the fate
of these bodies. They wander not only peripherally but centrally. Rarely we meet one which is
three or four times the average size, having a small chromatin spherule in its center. In later
stages they are present in far less numbers.

* For the opportunity of studying the crayfish development af this time I am indebted to the kindness of my
friend, Dr. William Patten, who sent me a number of important stages collected at Milwaukee.

*.

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 429

Reichenbach thus summarizes his observations on the “‘ sekundiire Mesodermzellen :”

Die fraglichen Elemente sind als Zellen zu deuten, deren Kerne nicht immer die Beschaffenheit gewohonlicher
Zelikerne haben, dieselbe aber friiher oder spiiter erlangen (Fig. 20, m, m?, Platexxvit). Sie nelmen ihren Ursprang
innerhalb derjenigen Entodermzellen, welche die ventrale Wand des Urdarmsiickchebs zusammensetzen durch eine
niiher zu erforschende Art endogener Zellbidung, bei welcher die in der Mehrzahl in den Elementen des Entoderms
vorhandenen Kerne eine wichtige Rolle zu spielen scheinen. In den dem Stadium D vorangehenden Entwicklung-
sperioden hat jede Entodermzelle meist nur einen Kern; dies trifft auch noch zum Theil fiir Stadium D zu. Bald ver-
mehren sich aber die Entodermkerne ganz erheblich und endlich beginnen die sekundiiren Mesodermzellen aufzutreten.
Wenn eine gréssere Zahl der sekundiiren Mesodermzellen in den Entodermelementen liegen, so scheint das Kernma-
terial verbraucht zu sein. Es wandern nun aller Wahrscheinlichkeit nach diese Zellen, deren Kerne anscheinend
noch in der Metamorphose sich befinden, aus dem Entoderm aus und begeben sich unter die Embryonalanlage. Die
ketreffenden Contouren des Entoderms lassen oft noch Spuren dieser Wanderung erkennen. Ob sie wirklich aktiv
auswandern oder auch ausgestossen werden, ist nicht festzustellen gewesen. Sie begeben sich nun unter die iibrigen
Mesodermzellen und sind bald nicht mehr von ihnen zu unterscheiden. Aus diesem Grund fiihrte ich fiir sie den
Namen ‘‘sekundiire Mesodermzellen” ein, wiihrend die ilteren Urmesodermzellen als primiire bezeichnet werden.
Da die letzteren die Tendenz zeigen, za kompakteren Massen zu verwachsen, so darf man wohl vermuten, dass die
sekundiiren Mesodermzellen die Blutzellen liefern werden (54, p. 36).

It is interesting to notice that in Alpheus, Astacus, and Homarus degenerating cells appear
in greatest force at about the egg-nauplius stage, and from that time on their numbers begin to
wane. In Astacus, Reichenbach first noticed the “‘ sekundare Mesodermzellen” in stage D (that
is, when the optic disks, the thoracic-abdominal plate, and the mandibles are outlined), which nearly
corresponds to Stage Iv of Alpheus. In stage D the bodies in question are most abundant under
the optie disks (Kopflappen) and in the region of the upper lip, but become more generally dis-
tributed in the egg-nauplius. _

According to Reichenbach, “ gastrulation” takes place after the optic disks are formed, but
unfortunately his paper is incomplete at a very important period, namely, from the late yolk-pyra-
mid stage of segmentation, when the protoplasm is at the surface, to the time when an embryonic
disk or plate (Entodermhiigel or Entodermscheibe) has been formed. It is impossible, therefore,
to follow the history of the so-called “ white yolk elements.” He says of the latter:

Sie bestehen aus protoplasmatischer, feinkérniger Substanz und enthalten vacuolenartige Einschliisse, die ilnen
ein schaumiges Aussehen geben; ich habe sie als weisse Dotterelemente bezeichnet. Sie liegen entweder dicht unter
dem Blastoderm oder im Centrum des kugligen Eies und verschwinden sehr bald (Op. cit., p. 7).

According to my view these bodies correspond to the vesiculated elements (m, Fig. 20), and
both represent cells in process of dissolution. If Figs. 18 and 20 are compared (the latter being
a copy of Reichenbach’s Fig. 67) we will find a striking correspondence between these peculiar cell
products in both Astacus and Alpheus, a correspondence which is even more marked when the
comparison is made with the lobster.

Reichenbach emphasizes the statement that naked balls of nuclear material never occur free
in the yolk outside the endodermal sae. In this yolk they always have a ‘cell body” as K, Fig.
20. It is an easy matter, however, to distinguish naked masses of chromatin, minute spherules,
or smaller granules in the yolk of both the lobster and Alpheus.

My studies of the lobster are not yet completed, but from the observations which have already
been made I draw the following conclusions: In Alpheus, the lobster, and the crayfish similar
bodies make their appearance at nearly similar times and play a similar réle. They are derived
from all three layers of the germ, and in Alpheus minor degenerative products make their appear-
ance in the segmentation stages. They tend to break up and ingest the yolk and to produce in it
a chemical change, possibly in order that it may be more easily assimilated by the other embry-

~ onic cells. Having performed this task they degenerate; they are converted into a substance
resembling yolk and function as nutrition. That any play a formative réle, giving rise to blood
cells for instance, as Reichenbach supposes, there is no direct evidence. The vitellophagous func-

’ tion seems to be in abeyance in Alpheus, but in all cases the yolk is comminuted and chemically

changed in the neighborhood of these bodies. Nusbaum (45), following Morin, believes that the
“white yolk elements” arise from the segmentation nucleus and migrate to the surface of the egg;
that they give rise to the “secondary mesoderm,” which are taken up along with the yolk by the
ameeboid, endodermal cells. This is reversing the account, and, in so far as the origin of the “see-
ondary mesoderm” is concerned, it is not supported, so far as [ am aware, by a single observation.

‘’

SE nee ee AVE a ee we eo. . fe ee *

rie bs

430 MEMOIRS OF THE NATIONAL ACADEMY CF SCIENCES.

Ishikawa (27) finds in Atyephyra after the close of the invagination stage, certain proto-
plasmic elements under the ectoblast, which he thinks may correspond with the ‘ white yolk ele-
ments” just referred to, and he also identifies’‘‘ secondary mesoderm cells,” but does not trace
their origin or function. * They are “ small granules,” easily stained by logwood solution, and some
are of considerable size and have a clear cell Satine: “hese are mostly aggregated in the
cephalic region between the involutions of the ectoderm cells, but are also found in all places.” In
time of appearance and in their position, he says they seem to correspond to the “ secondary meso-
derm cells” of Astacus. This short notice with his figures leaves little doubt that these bodies are
similar to those just described in Alpheus and Homarus. Fig. 62 of his paper represents a longitu-
dinal median section of the egg-nauplius, and may be compared with the same stage of Alpheus
(Figs. 104, 105), with respect to the general character and appearance of the degenerating cells.

I have noticed similar nuclear fragments in the egg-nauplius of a crab (Fig. 113, Pl. xi), and
Lebedinski (34) has deseribed ‘secondary mesoderm” in the embryo of the Mediterranean sea
crab, Hriphia spinifrons. According to this observer they are found in all stages from the “ gastrala”
on, to the egg-nauplius; they are derived from ectoderm, and probably give rise to blood cells.
In the stage with one pair of maxillipeds these elements are in active proliferation :

Man findet, die Zellen desselben bieten verschiedene Momente und Zustiinde des Zerfallens dar; dieses Zerfallen
der Zellen steht in genauen Zusammenhinge mit der Entstehung der Blutkérper.

He further says:

Ueber die Bildung des Blutes kann ich nichts bestimmtes mittheilen. Im Stadium des ersten Paars kieferfusschen
sind die ersten Blutkérperchen vorhanden, welche zum ersten Mal im Bereiche des Herzens vorkommen, wo sich auch
am friihesten das sekundiire Mesoderm riickzubilden beginnt.

From these quotations it appears that the “secondary mesoderm” shows sigus of degenera-
tion, and its conversion into blood cells is an unverified inference. It seems more probable that
the structures in question correspond with similar bodies already noticed in Alpheus, Homarus,
and other Decapods, and that in all cases they have to do primarily with the dissolution and not
with the construction of cells.

Wheeler (67) in his careful paper on the development of the Cockroach and Potato beetle
(Blatta germanica and Doryphora decemlineata) describes an interesting case of the decomposition
of nuclei, which bears a close analogy to what takes place in Alpheus and probably also in
Astacus. In Doryphora two masses of endoderm are found, one under the stomodum the other
under the caudal plate. At both these places numerous cells which originate in the endoderm
pass into the adjacent yolk and disappear. The process of dissolution is described as follows:

The karyochylema becomes vacuolated, probably with substances absorbed from without, to jndge of the larger
size of some of these nuclei, while the chromatin ceases to present the threadlike coil and becomes compacted into
irregular masses between the vacuoles. Finally the vacuoles fuse and the masses of chromatin, formally numerous,
agglomerate to form one or two large irregular masses which usually apply themselves to the wall of the clearly vesie-
ularnucleus * * * In the last stages seen the masses of chromatin lie between the yolk bodies, all other portions
of the nucleus having disappeared. They still take the deep red stain, but finally become comminuted and disappear
in the intervitelline protoplasm,

The vesiculated elements recall similar bodies which appear in Reichenbach’s plates. Thus
the element t, Fig. 88 of Wheeler’s paper, where the chromatin is applied to the walls of the
nucleus, strikingly resembles nucleus i, Fig. 20 (see this paper), where the chromatin i is similarly
disposed around the wall of a vacuole.

Bruce (10) figures certain yolk cells undergoing what he considered to be endogenous cell
division in an advanced embryo of a spider, and compared it with the endogenous cell division
which Reichenbach describes as taking place in the endoderm cells of Astacus.

The disintegration which has been attributed to the leucocytes of the mammalian blood
affords an interesting comparison with the phenomena which have been described for the Arthropod
embryo. Howell’s careful observations (25) support the view that the multinucleated leucocytes —
are disintegrating cells. ‘The leucoblasts enter the lymph stream, and eventually reach the
blood as unicellular leucocytes.” Here they undergo changes, acquire amceboid movements, while
the nuclei elongate, become constricted, and finally fragmented. ‘The multinuclearstage * * *
is probably followed by a complete dissolution of the cell.” Howell adopts the highly reasonable

:!

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 431

view that the nuclear fragments persist for a while in the circulation as the blood plates, and
considers it probable that the latter take some part in forming the paraglobulin of the blood. If
the blood plate is then a degenerate body, it may be compared to the spore-like masses of chro-
matin, which are discharged from the disrupted cells in the lobster or crayfish embryo.

VII.—THE ORIGIN AND HISTORY OF WANDERING CELLS IN ALPHEUS.

The wandering cells in Alpheus have a triple origin, from the blastosphere, from the invagina-
tion, and from the thoracic-abdominal plate. Those which arise from the blastula at the close of
segmentation are, perhaps, the representatives of a primitive endoderm. Following the invagina-
tion, a thick pad of cells is formed, the ventral or thoracic-abdominal plate. From this plate a
general migration of cells occurs on all sides inte the yolk (Pls. XxxuI-xxxv). While there is a
great tendency to migrate to parts underlying the embryonic area, the cells nevertheless wander
to all parts of the egg, even to those most remote from the embryo. The first of these wandering
bodies which originate from the blastosphere have been called “‘primary yolk cells.” The latter
classes may be called “wandering ceils.” Since these classes can not be distinguished after a
certain period, I refer to all cells which move about in the yolk and have no direct connection with |
the thoracic-abdominal plate, and the parts of the embryo in front of it as wandering cells. Ihave
been somewhat at a loss to find a suitable term for these bodies, since there are obvious objections
to the use of “yolk cells” or “yolk nucleus.” Where these terms have been employed in the present
paper, they must be understood to refer to the wandering cells which have been defined above.
The term “embryonic nuclei” is used for convenience merely to discriminate the remaining nuclei
of.the egg from those of the wandering cells.

The object immediately in view is to determine the fate of these wandering cells, to ascertain
what formative réle they play while the mesoderm, and more particularly the endoderm, are being
differentiated into definite cell layers. In the following account, cells which have parted all con-
nection with the thoracic-abdominal plate and have entered the yolk are enumerated as wandering
cells. In an earlier part of this paper I gave an account of the origin and supposed fate of the
wandering cells, the general conclusion being that in the early stages (Stages I1I-v) they pass
from the yolk to the embryo and to the extra-embryonic parts* of the egg, and contribute to both
mesoblastic and entoblastic¢ structures.

A number of friends to whom I showed my sections objected to this interpretation on the
ground that these wandering cells could be regarded with equal probability as originating, in some
measure at least, in the opposite way, that is, as budding from superficial cells not concerned with
the thoracic-abdominal plate, and migrating into the yolk. A careful study of successive stages

_ would not support this idea, but the objection could not be satisfactorily answered, and neither

view could be readily proved. I therefore-undertook a renewed and wore precise study of the
wandering ceils in Alpheus, and I think that their fate has been definitely settled.

The number of wandering cells which occur in the yolk, and the number of “ embryonic cells”
(that is, all the other cells of the egg) have been enumerated in five different stages, including
seven different embryos, from the period of delamination at the close of primary yolk segmentation
to the early egg-nauplius condition (Stages 11-v.) This covers the most important period so far as
the wandering cells are concerned. ~Lhe rate of increase of both wandering cells and embryonic
cells has also been determined for the successive stages, and the data are given in Table I.

* There is a certain convenience in thus referring to the embryo proper and to the less differentiated regions, while
it is understood that all the cells constitute the embryo.

432 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 2

TABLE I.— Showing the number of nuclei in yolk, and the number of other “embryonic nuclei,” and the
relative increase and decrease in these bodies from the close of yolk-segmentation to the egg-nauplius

period.
3 aa 2S ao Be <i a aM | Be 1e2
8 Bs 23 2% 5.8: i of @ tb Ae ba} SA
Ba {oe (| ee | Ge | yee cee oso Nemes
Stage. TON egos oF Ser) ean se fm 27S 56 BIS penta |S
8, | 23; | 25. os mA aS As gz | 22 | 285
an Sart te iS Sn8 =3 =2 on os $:'s
& | 535 |832| BF | 538] 22 | 82 |. S8| 35 | Sua
4 A A ahmed oe a a 4s }as 14
Il. Delamination (Figs. 38-45, 46, Pl.
DO: @'@) ae epars oy eae er es on ee Cec got) Barnes eo Ae te fini Ove eerie es eB See es Seer
IL. Invagination)(@) Figs. 49-55, Pl. xxx1 | *37 30... -| 421] 187]. 458] 140 Siren 324
3 ow 0(b) Figs. 49-55, P1. xxx | 737 oe ee 430 146 467 149 Bon eae 34
III. Optie disks (Pls. XXXII, XXXIII).----. 199 162 5\cee ese 1736 306 935 468 co) an he es 42
IV. Firstantennz,mandibles (Pls. Xx XIV,
REV) Saeoegee ea aes cee 240 Ue ee t915 179 | 1,155 220 tS oe 20
(a) Figs. 34,Pl. xx1x;
101-105, 107, pill 199 |... 41 | +2,989 | 2,074 | 3,188 | 2,033 |..-.-. 21 | 69
V. Early egg-nau-) XXXIX...-......-.
plius -.....-.](b) Figs.34, Pl. xx1x;
101-105, 107, PLS} 128 |....... 112 | +2,230 | 1,315 | 2,358 | 1,203 |..._.- 874 | 59
Rs so ee |

* Primary yolk cells.
+ Number obtained by method described bolow.

The distribution of the wandering cells and of the embryonic nucle? is also illustrated by a
series of curves, constructed in the following manner: Each vertical row of the smaller squares
corresponds to a section of the ovum (Sections Nos. 1, 2, 3, ete.), whileeach square in this row
represents a single nucleus. The number of nuclei in a section is shown by the number on the
line where the curve makes a bend or intersects the middle of the lower side of a square (nuclei
Nos. 1, 2, 3, etc.). Thus where the descending line of the curve in Fig. 5 stops in section No. 2,
making an angle in the fifth vertical square, counting from the upper base line, this implies that
in the second section of the egg, corresponding to this vertical area, there were five nuclei which
did not appear in the following or preceding section.

The number of nuclei were determined in the following way: Camera-lucida drawings were
made of every section of a given series on thin paper and each nucleus was marked. Then, by
superimposing upon each drawing the drawing of the section immediately following, every nucleus
new to that section could be determined in the early stages with absolute certainty. The number
of primary yolk cells and wandering cells were thus counted in all stages. In the older embryos
(see numbers marked with dagger in Table 1, Stage mI-v) where this method became impracti-
cable with reference to the total number of embryonic nuciei, their number was estimated in a
different manner. The nuclei appearing in each section were counted and the total number of
nuclear sections was thus obtained for the whole series. Then the percentage which the actual
number of nuclei in the egg bore to the total number which appear in sections could be determined
approximately by the method described above applied to a number of lateral sections, that is, by
actual count of nuclei in a favorable part of the series. The percentage which the actual number
of wandering cells bears to the total number appearing in section could be exactly determined and
compared with the former estimated percentage. The percentage which involved the wandering
cells was in the average of all stages a trifle the sma!ler, showing that the yolk cells were, on the
average, a little larger than the other embryonic nuclei. In Stage 1 before invagination the super-
ficial nuclei are the larger, while after invagination the difference is at first very slight indeed,
In Stages 11 and Ivy the wandering cells are markedly the largest in the egg, while in Stage Vv they
either equal or fall slightly below the size of the other embryonic nuclei.

This method presupposes a perfect series of sections of uniform thickness. These conditions
were approximately fulfilled. The egg (4™™, or 4; inch in diameter) was cut, on the average, into
57 sections, each section being ;4,™™ in thickness. The size of the egg, neither too small nor too
large, rendered this species (called throughout this paper the Bahaman variety of Alpheus heter-
ochelis) most favorable for study so far as technical difficulties were involved.

bas Ssh

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= MEMOIRS OF THE NATIONAL ACADEMY CF SCIENCES. 433

Stace II.—Close of yolk segmentation—Formation of yolk cells, followed by invagination.—A
surface view of this egg is given in Fig. 47, Pl. xxx. The curve (Fig. 5 of text) shows that the
blastodermic cells are distributed very uniformly. In other words
the embryonic area is not as yet marked off. The distribution of
the primary yolk nuclei, of which there are exactly thirty-four, is
shown in the constructed figure (Fig. 3), which represeuts the egg
as it would appear if the yolk were transparent and the nuclei
opaque. The distribution of these nuclei through the egg is given
more completely by the curve (Fig. 4). The only questions which
need detain us in this stage are, how do the primary yolk cells
arise and from what part of the surface do they come? Karyo-
kinetic figures, which abound among the surface nuclei, ought to
furnish an immediate answer to the first question. In this egg no
less than sixteen nuclei are met in various phases of division, fif-
teen of these belonging to the superficies and one to the central Wie. 3.—Diagram of egg in delamination
portion of the yolk. » Clusters of two and rarely of three nuclei also “t8* constructed from serial seetions,

P showing all the primary yolk cells. For
occur at the surface, showing that cell division is active. In every details, see Table 1, Stage m (Delamina-
case the cleavage is radial or perpendicular to the surface, and in no ‘)-
instance have I seen an unambiguous case of delamination (v. Pl. xxx). Ityis possible, however,

eee Peeeeseeans HE

Pein Sagi Ba “ ba
ba WP | |7l2\3\4lslel7lelolal7|2) Li LA Ae 612712129 ete 4263/4

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cde teat tadaseatad ado aos taste

Pal 514614 7148149

beta ps ei lela s(t | a -— YT Lt
SR SUR EES eRE sees |

Lt | Y aaee ERDSREaMe

i Fig. 4.—Curve constructed from serial sections, showing the distribution of the primary yolk nuclei in the egg represented by Fig. 3.
For further details, compare Table 1, Stage 11 (Delamination). A— Anterior; ’— Posterior.

co SESSSSSR508000000eRR00

PEEE
ae
o

Fic. 5.—Curve showing the distribution of nuclei at the surface (that is, nuclei of the embryonic cells, exclusive of primary yolk cells)
of the egg represented by Figs. 3 and 4. For details, see Table 1, Stage u (Delamination).

S. Mis. 94-28

434 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

that the primary yolk cells are formed in this way rather than by emigration, and that my failure
to detect the actual process is due to the fact that I did not sec-
tion exactly the right stage, the egg shown in Figs. 38-45 being
a trifle too old. In Homarus the primary yolk cells arise by
delamination, as I have already shown in a preliminary paper in
the development of this form (23, Fig. 5),

Sections of this stage show conclusively that the primary
yolk nuclei do not come from any one point on the surface, but
that the majority of them may come from a restricted area of
the egg. In Fig. 3 about two-thirds of the nuclei present are con-
fined to the lower (ventral ?) surface of the egg. They are in
various degrees of progress from the surface toward the central
parts, which the majority have already reached.

,. The formation of primary yolk cells is followed by the in.
in’ vagination and ingrowth of certain cells at the surface. The his-

Fic. 6.—Diagram of egg in invagination tology of the embryo at this phase is given in Pl. xxx1, and Fig.
stage, ee peter ee 6 (of text) is constructed from the entire series of sections to show
For details of this egg, see Tablet (nq), ll the primary yolk nuclei present. The plane of the paper (sup-
Invagination, In—pointiof invagination, posing the drawing to represent a sphere) nearly passes through
nee ea eae eae the point of invagination (in.).

In order to test the accuracy of the method, two eggs of this stage were studied (a, 11 and b,
ft of Table 1), and the results show a remarkable agreement. Thus there are exactly thirty-seven
primary yolk nuclei in each egg, and the total difference in the number of embryonic nuclei in the
two eggs is only nine. Curves were constructed to show the number and distribution of yolk nuclei
and embryonic nuclei in both eggs, and the two are introduced here because of the striking simi-
larity. Figs. 7 and 8 are constructed from the egg seen in Fig. 6(11, a, of Table 1). Figs. 10 and
9 represent corresponding curves constructed from the second egg (11, b). The two sets of curves
tell exactly the same story in each case, and it is not necessary to dwell upon it.

Fic. 7.—Curve constructed from serial sections, showing the distribution of the primary yolk nuclei in the egg represented by Fig. 6.
(See Table 1, Invagination stage, U1, a.) .

The bulk of the primary yolk nuclei are placed near the center. Of the thirty-seven nuclei in
a, 11, twenty-two are in the ventral (?) hemisphere of the egg, and fifteen in the dorsal. In egg b,
Il, twenty-one nuclei are situated in the ventral half and sixteen in the dorsal. Thus these yolk
nuclei incline toward the ventral side of the egg, and hence, as already inferred, are probably
derived in great measure from that part which corresponds to the embryonie area.

The curves showing the relations of the embryonic nuclei (Figs. 8 and 10) read from end to
end of the embryo (posterior to anterior), the sections being transverse to the longitudinal axis.
The greatest depression naturally occurs in the region of the thoracic-abdominal or ventral plate
(Ab. P.), near the center of which is the point of invagination. In front of this there is a more
extensive, but less depressed portion, corresponding to the embryonic area (#. A.). The number /
of cells entering into the ventral plate at this time are shown in Table 11.

: ; MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES,

sere SUSUEGESESESEREEEEE
, (251261271 a ae Jada/ Aa zee é

sdesssasaaasttnaaE
Wedcih |AVG |7 iaiatet A//
PE Bas Ae
PR =
el] |
Bul

. Fic. 8.—Curve showing distribution of all nuclei, exclusive of primary yolk nuclei, in the same egg a8 represented by Figs. 6 and 7.
(See Table 1, Invagination stage, U, @.) A, Anterior; P, Posterior; Abp, Ventral plate; LA, Embryonic area.

| :
:
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Fie. 9.—Curve showing the distribution of the primary yolk nuclei in the invagination stage, egg No. u, b, Tablet. (Compare with Fig. 7.)

aeeeue Het Et

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PCE Sse CECE EPS

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Abp. As
7 . Fic. 10.—Curve showing distribution of all nuclei, exclusive of primary yolk nuclei, in the same egg as represented by Fig. 9, (See 11,
b, Table 1, and compare with Fig, 8.) A, Anterior; P, Posterior; Abp, Ventral plate; LA, Embryonic area.

,
436 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.
TABLE II,
Nnelei at Nuelet in Total num- Prather Remaining Total num-
Stage. pur ieee low sur- SEE nae! yolk nuclei. bad he ee
ees Se se eee cael | =
aunts 5D) =e spon 60 mats 37 305 | 458
LY ae 52 | 48 100 37 330 | A467

Of the forty-eight to sixty cells which appear below in surface at this time in the ingrowing
cell mass, a large number (twenty in b, 11) are parting company with their fellows and beginning to
migrate into the yolk. So that at this stage the primary yolk cells receive their first recruits from
the ventral plate.

Srace III.—Optic disks and thoracic-abdominal or ventral plate. —Wandering cells now become
a very marked characteristic of the Alpheus egg (Pls. Xxxtl, Xxxut). Wesee by Table 1 that the
total number of yolk nuclei has come up to 199, an increase of 81 per cent against an increase of
only 42 per cent on the part of the other embryonic cells. In other words, the wandering cells have
increased nearly twice as rapidly as the other nuclei of the egg. It is, perhaps, hardly necessary
to point out that this rapid gain is due to at least four possible causes: (1) to the multiplication of
primary yolk cells, probably the least important; (2) to the irruption into the yolk of invaginate
cells, or cells derived from these, the most important source; and (3) to the multiplication of the
latter in the yolk itself; and (4) to migration from the ventral plate, which is formed by a thiek-
ening about the point of invagination.

The curve showing the distribution of wandering cells at this stage (which is not figured) is
nearly bilaterally symmetrical. The greatest depression is in the region of the thoracic-abdominal
plate, while on either side of this there is a marked drop in the curve, answering to nuclei which
underlie the optic disks and the parts behind them. (Compare Fig. 11 of text.)

A considerable number of cells have migrated to points near the surface both behind aie
ventral plate, to either side of it, and immediately in front of it (see Figs. 56, 58, 59, 60). A very
few have wandered out to points just beneath the optie disks. Quite a number have started in the
direction of the dorsal surface of the egg, but none have reached it.

STAGE IV.—Rudiments of First Antenne and Mandibles.—This is the most interesting stage
in some respects (see Pls. XXXIV, XXXv), since it is critical so far as the fate of the wandering cells
is concerned,

edtiok W2| Hla|slalslalz|alebolpelalal selva 2/ aia EAP 13213313 3dadle/\a2 sA5/ EP
+ +—__}
. 2|2
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4
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imal Zz
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Fic. 11.—Curve showing the distribution of wandering cells in Stage TV, rudiments of first antennz and mandibles present. (Compare —
Pl. xxx1y, and for numerical details, see Table 1, Stage 1v.) Abp, region of ventral plate; O D, Region of optic dises. :

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 437

Table 1 shows the remarkable fact that the percentage of increase of wandering cells, which
in Stage 111 was twice as great as that of other embryonic nuclei, has now dropped until it is actually
less than the latter. This means that the wandering cells are multiplying less rapidly or that their
numbers are being depleted. The relative increase of yolk nuclei from Stage I to 111, and from
Stage mr to Iv, namely, 81 per cent and 17 per cent (showing a marked falling off), is not specially
significant, since these numbers depend largely upon the age of the embryo or time which elapses
between successive stages. But this element does not enter into the relation which exists between

F = the relative increase of wandering and embryonic cells in the same egg, expressed by 81 per cent
4 and 41 per cent, respectively, in Stage 1 and by 17 per cent and 20 per cent in Stage Iv.
; The curve constructed from Stage tv (Fig. 11) shows the wandering cells much more widely

‘ ; diffused through the egg than at any earlier period. The thoracic-abdominal plate is no longer
. sharply marked off from adjacent parts, and a considerable number of nuclei underlie the optie
= disks.

In this egg there are thirty-seven nuclei in various phases of karyokinesis (Figs. 70, 75); two
belong to the yolk, three to the deeper cells of the thoracic-abdominal plate, and the rest to the
| ; E surface cells of the embryo. In the optic-disk region a very few cells appear to be delaminating ;
: the rest are cases of radial division. Cell disintegration has not yet become a disturbing factor in
oy the enumeration of cells. There are but two nuclei in the egg, one in the yolk, the other in the

deeper part of the ventral plate, which show any traces of dissolution. .

The above facts lead to the conclusion that the wandering cells are being rapidly depleted

at this time, that they leave the yolk in considerable numbers and attach themselves to the
growing embryo and to the extra-embryonic surface of the egg. They thus warrant our interpre-
tation of a cell like ye, Fig. 70, or ye’, Fig.71, as a migrant from the yolk. While the wandering célls
: are being rapidly depleted, it does not of course follow that they never receive any recruits from
any part of the egg without the limits of the ventral plate, and it requires no very elaborate calcu-
lation to show that wandering cells are making early contributions to the mesoblast, but the study
of individual sections and the facts brought out in Table 1, prove beyond a doubt that the only
cells which enter the yolk, up to this time, arise from one of the three sonrces already named, the
: blastoderm, the invagination, and the ventral plate.
STaGE V.—Egg-Nauplius.—The early egg-nauplius stage 1s represented by two individuals,
one (V. a, Table 1) cut in transverse and the other (Vv. }) in longitudinat vertical planes. Respect-
ing the wandering cells we now notice: (1) that their numbers have markedly decreased; (2) that
they are far more widely and evenly distributed; and (3) that many are close upon or in contact
with the embryo or with the general surface of the egg.

In egg V, ) (Table 1) the number of yolk cells is only one hundred and twenty-eight, consid-
erably less than are present in Stage 111, a decrease of 87 per cent, while in the other egg the
decrease is 21 per cent. On the other hand, the rate of increase of embryonic nuclei is greater
than at any previous stage, 59 per cent in one egg and 69 per cent in the other. That this is not
explained by a large interval of time existing pervect Stages Iv and Vv is shown by the fact that
during the period (Stage Iv and Stage vy, b, Table 1) the total number of nuclei of the egg has
scarcely more than doubled, while the percentage of increase of embryonie nuclei has more than
4 trebled. Between Stages II, a, and 11, on the other hand, the number of nuclei has nearly donbled,
: while the percentage of increase of embryonic nuclei has risen from 324 to only 42.

How is this very rapid increase in embryonic nuclei and codrdinate decrease in wandering
cells explained in the egg-nauplius stage? The conclusion reached in Stage 1v applies here also,
with a certain restriction. The problem is now not a simple one, since perturbations caused by
the disintegration of nuclei appear to some extent in this stage. The diminution in che number of

q wandering cells is now due to two causes, to cell disintegration and to the gradual subtraction of
cells from the yolk by emigration. Disintegration of cells occurs both in the yolk and in parts of
theembryo. It is perhaps most marked near the line of contact of the yolk with the embryo. Yet
the embryonic cells are meantime making a rapid net gain. ;

We are thus warranted in our conclusion that the wandering eells, which spread far and wide
‘ through the egg, play a formative role in development, to a large extent at Jeast. This conclusion
is rendered certain by the changes which ensue between Stages 11 and Iv, already noticed. The

438 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

percentage of increase of wandering cells between Stages 1 and 11 is double that of the embry-
onic cells. Between Stages 111 and Ivy the increase per cent of wandering cells is less than that of
the embryonic cells, and up to this time cell disintegration is ruled out as a disturbing factor.

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Fig. 12.—Curve showing distribution of wandering cells in Stage y (Early egg-nauplius). (Compare Fig. 11, and for details, see Table /
I, Stage, 1b.) E A, Embryonic area; Mo, Mouth.

The second fact which was pointed out as characteristic of this stage, the distribution of the
yolk nuclei commensurate with that of the yolk itself, also points to the conclusion already reached.
This is well shown by two curves (Figs. 12, 13). In curve 13, which is constructed from a series

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GIONS

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7
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Jes
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Fic, 13.—Curve showing the distribution of wandering cells in Stage v,a.(v. Table1.) A, Anterior; P, Posterior.

of transverse sections, we see that wandering cells are most abundant in the thoracic-abdominal.
fold region and in that which answers to the future heart. We also notice the forward extension
of migratory cells beyond the anterior edge of the optic lobes. In cut 12 the lateral extension
of the nuclei on either side the embryo is well shown. The mouth is involved in section No. 28,

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 439
and the embryonic area is included between sections 14 and 41. The marked peripheral distri-
bution of the migratory cells is very significant. There seems to be a general movement of these
bodies to all parts of the superficies.

What is the ultimate fate of those cells which wander out to the surface of theegg? Fig. 34,
Pl. XxIx, represents part of a section of the extra-embryonic surface at this stage. Here is undoubted
ectoblast (Ep.), and cells (Y. C.), which have undoubtedly come from the yolk, are pressing against
the surface. Ina single egg one may meet with twenty or more such cells, as well as with cells
in various degrees of proximity to the surface. Do these cells (Fig. 54, Y. C.) eventually contrib-
ute to the mesoblast or ectoblast of the embryo? This question can not be answered by direct
observation, since it is clearly impossible to follow the fate of the individual cells. From all the
evidence which I have gathered I conclude that the wandering cells give rise to mesoblast—muscles
of body wall, connective tissue, and blood corpuscles, and, later, to the definitive entoblast lining
of the midgut. The part which the primary yolk cells play can not be decided, nor can it be deter-
mined whether degeneration is more characteristic of these elements than of the invaginate wander-
ing cells.

In a lobster’s egg at the delamination stage, equivalent to Stage 11, Table 1, I find 213 nuclei
present. Eleven of these belong to the yolk. Upwards of twenty, two of which are yolk cells, are
in process of division. Of the eighteen superficial or peripheral cells which are in karyokinesis,
two are dividing horizontally or delaminating. In the lobster the primary yolk cells degenerate,
in part if not wholly, at a very early stage, as already stated.

In the egg-nauplius phase it was noticed that wandering cells settle down upon the ectoblastie
bands out of which the nervous system is subsequently developed (Fig. 127, Y. C.). In this case
also it is impossible to ascertain with certainty the fate of such cells. They might form ectoblast
or mesoblast, but it is more probable that they contribute to the latter layer only.

It is evident that the history of the wandering cells is largely the history of the mesoblast
and entoblast. The mesoblast,* where it has been studied in Decapods, as in Astacus, is found
(54) to originate in certain swollen cells in or near the anterior margin of the “blastopore” or
pit. From this primary mesoderm cells are budded off, which extend forward in a more or less
continuous sheet over the ectoderm. It is possible that in Alpheus the wandering cells may serve
as a means of a precocious development of the mesoblast and entoblast. In connection with this
idea, it is interesting to recall the fact that in high temperatures of the trepics the developmental
stages are passed very rapidly. At Woods Holl, Mass., the late egg-nauplius of the lobster,
Homarus americanus, is from fourteen to sixteen days old, while a similar stage is reached by
Alpheus sauleyi at Nassau, N. P., in about seven days.

VIII.—THE DEVELOPMENT OF THE NERVOUS SYSTEM.

The nervous system can be referred back in the embryo to an early stage (Figs. 58, 62, 68),
when V-shaped ectoblastic thickenings unite the optic disks to the thoracic-abdominal plate. The
intervening space is gradually encroached upon until the optic disks are completely bridged by a
dense sheet of ectoderm. There is an apparent concrescence of the limbs of the V, and in the egg-
nauplius (Pls. XLI, XLII) these thickenings form a pair of more or less closely united cords, which
are separated on the middle line by a median longitudinal furrow. The shallow furrow is formed
by the swellings of ectoderm which correspond to the future ganglia, and extends from the saprace-
sophageal ganglia to the segment of the first maxille.

The nervous system of the egg-nauplius is not differentiated from the general integument, and
the ectoderm is still a single layer on the middle line in the maxillary region (Fig. 121), while at
the base of the first pair of antennex (Fig. 116) it has the appearance of an elliptical plate in trans-
verse section.

* Weldon, whose paper on the germinal layers in Crangon has been referred to, says truly that the difference
between invaginated cells is not sufficient to enable one to say that certain cells are endoderm and that others are
mesoderm, but be designates as endoderm all cells which are derived from the invagination, and restricts the origin
of the mesoderm to the lower layer cells of the ventral plate. Judging from the evidence which has thus far been
presented, the cells which he has marked endoderm, lying against the embryo and near the folds of the appendages,
are in my opinion to beinterpreted as mesoblast. The thoracic-abdominal thickening is composed of a pair of concave
‘‘neuro-muscular” or ventral plates, which correspond to, the single plate described in Alpheus,

440 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

The antennular ganglion is in close union with the optic ganglion and unites also with the
antennal ganglion which lies along the sides of the stomodzum, extending slightly behind it.

The histological differentiation of the nervous elements is not very considerable at this stage.
In the ectoblastic thickenings, out of which the nervous system is formed, we can distinguish three
kinds of cells: (1) the superficial cells, (2) the central cells, and (3) the accessory cells which come
from the yolk. These are best seen in a section of the antennular ganglion (Fig. 116). The outer
cells (1), which form the integument, possess very large granular nuclei. Some of these, on either
side of the middle line, can be distinguished beyond doubt as the nuclei of those large ganglion
cells so characteristic of later stages (see Figs. 146, 147, 169, 170, 191, g. ¢.). They possess a more
or less definite cell body of a round or oval contour. In preparations this is fine-grained and, like
the nucleus, stains but feebly. The weak stain of the nucleus is due to its very fine and loose
chromatin reticulum. Karyokinetic figures attest to the multiplication of these cells (Fig. 191), and
it is highly probable that they give rise to similar cells which occur in both larva and adult. But
what is remarkable in the earlier stages is their enormous size and their peripheral position.
Reichenbach ealls attention to similar cells in the embryo crayfish, which also arise from the outer
layer of ectoderm cells and for a long time help to form the outer wall of the body. It is hardly
probable, however, that these cells are relatively more highly differentiated in respect to their
ultimate function than any of the surrounding cells which take part in the nervous system. The
central cells (2) are the ordinary ganglion cells of the cortex which inclose the fibrous masses.
They have smaller and less regular nuclei, which stain very heavily. Cell boundaries are entirely
effaced, and the cell protoplasm is reduced to a minimum. The accessory cells (3) rest on the
dorsal surface of the thickening, and represent indifferent or wandering cells derived from the
yolk (Fig. 116, cts., Pl. xLI, mes.). I am not prepared to say that any of the ultimate nervous
cells are derived from this source, but I am certain that cells migrate from the yolk and attach
themselves to the ectoblastic thickening out of which the nervous system is formed, and that they
multiply by indirect division. It is probable that the connective tissue sheaths of the nervous
system may be due, to some extent at least, to such cells. The ectoblastic thickening is increased
by the radial division of superficial celis and by the horizontal division of the deeper cells.

In the larval and adult stages the large balls of fibrous substance, particularly those of the
brain, are surrounded by a delicate cell layer or internal envelope. The nuclei are small and
spindle-shaped and form an exceedingly thin sheet. It is possible that this represents intrusive
mesoblast, derived from the yolk. Reichenbach states very positively that in Astacus connective
tissue cells are squeezed into the fiber balls and eventually surround them. I have no positive
evidence to show that the cells in question are not of ectodermie origin, but the behavior of the
wandering yolk cells renders it probable that they should rather be referred to the mesublast of
the embryo.

The Punct-substanz of Leydig or fibrous substance is not present at this time, unless it is
represented by a very delicate reticulum in the midst of the nerve cells of the ganglia of the first
antenn on their dorsal surface next to the yolk. Degenerating cells (Fig. 114 s') oceur in abun-
dance close upon the optic ganglia and the ventral ectodermal thickening.

It may be interesting to notice that the structure of the antennular ganglion (Fig. 116) is
similar to that of the optic lobe. In either case there is a peripheral tier of cells possessing large
granular nuclei, an inner layer with smaller nuclei, and an imperfect layer of investing cells.

Passing to Stage vil (Pl. XLIV) we find the nervous system still very rudimentary. The super-
ficial cells, particularly in the region of the optic lobes and the antenne, have large nuclei, which
can be seen in the act of division, dividing both longitudinally, thus increasing the superficial
area of the plate, and also tangentially, in this way adding to its thickness. The very intimate
union of the optic ganglion (Fig. 132 G. L.) with the antennular ganglion (S. O. G.) is still very
noticeable, and the delicate investment of these parts on the side of the yolk (mes.) is more
marked.

Punct-substanz has definitely appeared in the supra-cesophageal ganglion where there is a
marked transverse commissure, and can even be distinguished in the w@sophageal commissures.
It forms a very delicate protoplasmic reticulum, and there can be no doubt-that the fibrous sub-
stance of this part of the nervous system arises as an outgrowth from the protoplasm of ectoderm
cells.

J] oo

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 441

The paired structure of the ectodermal plate is well shown in the antennular ganglion on a
jievel with the transverse commissures, or even in front of this, where paired masses, with small,
deeply dyed nuclei, are separated by a median sheet of much larger and clearer cells. This may
possibly correspond to the mittelstrang, referred to again.

Shortly after this (Pig. 159) the ganglia are blocked off by a series of superficial constrictions.
At least seventeen such ganglionic segments can be counted, beginning with the optic and supra-
esophageal ganglia and passing to the last abdominal segments. The ganglionic blocks are
formed rapidly trom the front backward. The ganglia of the first antennze are now the most con-
spicuous part of the nervous system, unless we accept the large optic ganglia. There is a broad,
transverse, fibrous commissure in the antennular segment, which is still more prominent at a little
later period (P1. XLVI), when eye pigment is forming. From this commissure longitudinal rods
extend forwards and unite the brain with the optie ganglia, while similar rods grow backward and
form the fibrous axis of the circum-cesophageal commissures. j

The plane of section in Fig. 148 passes just in front of the esophagus and through the roots
of the first pair of antenns (A 1), which should appear in the drawing as continuous with the
integument. The ganglionic cells, which are directed toward the appendages, represent the anten-
nular nerves, and are more apparent in the following section. The antennular ganglion is both
preoral and preantennal, lying in front of the first pair of antenne, which it supplies with nerves.

The brain and ventral nerve cord are now plainly separated from the hypodermis, and are
bathed throughout their extent with blood plasma, in which numerous blood corpuscles are seen
floating at every point. Giant ganglion cells have become most conspicuous in the optic region

-and at the periphery of the brain next the hypodermis.

The brain is partially divided in front next the optic ganglion by a delicate membrane, which
forms a median superficial partition between its two halves. This is continuous, with a delicate
envelope, which in some cases can be detected about the brain, and is like that which covers the
optic ganglion and nervous system generally. A similar non-cellular membrane at this time
divides the retina from the optic ganglion, and is continuous with the cuticular sheath of the
latter. The intercepting retinal membrane is directly continuous with the delicate basement
membrane of the hypodermis. The cuticular sheaths of the nervous system are present in the
embryo (Figs. 157, 168 pr.), the larva (Figs. 175, 176), and the adult. It may not seem easy to
harmonize this account with the view already taken that the wandering cells attach themselves
to the nervous rudiments and form a delicate investment to them (Figs. 129, 131 mes.). Such
is plainly the fate of some of the wandering cells, but the number of cells is probably too small
to form a continuous structure, and it is possible that the delicate membrane secreted by the
ectoblast may serve as an accession to that formed by mesoblast.

With respect to insects, Wheeler (67) conclades that in Doryphora the “outer neurilemma”
is ectodermic rather than mesodermic in origin, sincee—

Shortly after the separation of the nerve cord from the integumentary ectoderm, it sheds from its surface a deli-
cate chitenous cuticle simultaneously with the shedding of the first integumentary cuticle. This cuticle, which is
separated from the surface of the outer neurilemma, and even from the surfaces of the main neural trunks, is after-
wards absorbed.

At the time when the nervous system has completely separated from the integument there is a
slight ingrowth of ectoderm cells along the midventral line, most pronounced between the ganglia,
andthe appearance of a corresponding constriction on the side next the yolk. In transverse sec-
tion the nerve cord is somewhat hourglass-shaped. This may be due to a mechanical necessity,
arising from a more rapid development of the nerve cells in the lateral masses than in the other
parts.

Ectoblast cells derived from the integument appear to be infolded between ganglia (see Fig.
157—a thin sheet of cells, with spindle-shaped nuclei bending in between the last thoracic and
first abdominal ganglion, in the lower right hand portion of the figure), but these infoldings may
be somewhat deceitful, since they are straightened, to some extent at least, with the growth of
the abdomen (Fig. 168, abg. I). On the ventral surface of the thoracic region {Fig. 163) spindle-
shaped nuclei are seen wedged between the nerve cords on the middle line. It is not, however,
certain that these cells are ectoblastie, since the sternal blood sinus is already formed, to which

Cae ee eee ee, oF wk ee 4 =

442 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

blood cells have penetrated, and here eventually the sternal artery is developed. While the evi-
dence is not conclusive, we have only to decide between the former conclusion—that the intrusive
tissue is derived from the wandering cells, and is to be referred to mesoblast, or the view that it
represents differentiated ectoblast.

A general account of the structure of the nervous system of the larva is given in the first
section. Further than this the details of development have not been followed.

In comparing this account with that given by Reichenbach for the crayfish, Astacus fluviatilis,
there are numerous particulars in which there is no agreement, while in some important matters
we are in accord. ‘

I find in Alpheus the oral invagination occurring on a line drawn between the bases of the
antennular buds, and I bave a great many preparations of the eggs of the lobster. Homarus ameri-
canus, which show the earliest traces of the stomodw#um. Before the first antenne are folded,
when they are distinguished as dense patches of cells, some eggs show the primitive mouth as a
minute circular pit, lying nearly on a line drawn between the centers of these proliferating cell
areas, but, so far as my observation goes, never distinctly in front of them.

The relative positions of the mouth and first pair of antenn shift very rapidly during the
early period of their growth, which precedes the fully developed egg-nauplius condition. The
pit.elongates and becomes a transverse furrow, and by the time the first pair of antenne are
clearly marked off as rounded buds, and before the second pair are raised into folds, the mouth is
still on a line with the first of these appendages. When the second antennie are elevated into
folds the mouth is behind the buds of the first pair, or on a line between their posterior edges.

Reichenbach (taf. 1, Fig. 7a, Lb.) describes and figures a cell thickening between the “ Kop-
flappen” of the crayfish embryo (Stage E), which he considers the beginning of the labrum. His ~
sections show that below this point a mass of ectodermic cells occurs, which 1s interpreted as the
“Vordarmkeim.” The mouth is not represented as appearing until the following egg-nauplius
stage (Stage F. Compare Fig. 66 and p. 100, § 7, ‘‘ Der Vorderdarm”), when it occupies a position
exactly comparable with that observed in the lobster. I therefore can not agree with Kingsley in
saying that Reichenbach ‘has all the appendages at ‘first distinctly postoral.” While the posi-
tion of the Crustacean appendages may have been primitively postoral, it may be questioned if
in the higher Crustacea the first antenne ever arise behind the mouth invagination.

Kingsley describes.the position of the mouth in Crangon as distinctly postoral, but an inspec-
tion of figure 11 of his paper, leaves some doubt as to whether he is uot mistaken in this particular.
A single rudimentary appendage, marked as the first anteuna, is represented as occupying nearly
the entire space between the optic disk and thoracic abdominal fold. This does not agree with
my own preparations,* and since in Alpheus, Homarus, and Astacus the mouth does not appear
until a dense stratum of cells carpets the intermediate space between the optic disks and lateral
cords, there is some difficulty in interpreting the cluster of cells marked m, in Kingsley’s paper, as
the invagination of the mouth.t §

In Alpheus, Homarus, Astacus, and probably in Deeapods generally, the ganglion of the first
antenna cannot be said to be postoral, but its development begins nearly on a line with the
invagination of the primitive mouth. The ganglion of the second antenna is developed behind
the primitive mouth, but gradually shifts forward with its appendage until it comes to lie, in the
larva, considerably in front of the mouth. In this movement, the ganglion however outstrips the
appendage. The ganglia of these two appendages unite to form the brain or supra. cesophageal
ganglion. The ganglion of the first pair of antennz is constricted into two portions marked by
an oblique, transverse line at the surface. The anterior of these parts Reichenbach calls the

*I have preparations of the eggs of Crangon vulgaris, in various stages of development, from the segmentation
onward. In one egg, which is somewhat more advanced than that of figure 10 (31), or than the Alpheus in Fig. 58
of this paper, the optic disks and ventral plate are dense patches of cells. On either side of the ventral plate and in
close relation to it there is a marked area of cell proliferation which represents the mandible. In the space between
this and the antenna the nuclei are more scattered, but the karyokinetic figures show the activity of cell division.
In a late nauplius stage the stomodweum is on the middle line between the first and second antennw, and the anten-
nular ganglion is segmented into two parts on each side, as shown for Alpheus in Fig. 110.

t This criticism is supported by Weldoun’s observations on Crangon, who, with reference to this subject, says:
“The first antennz are evidently prworal from the very earliest period at which the mouth is visible.” Op. cit.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 443
“vordere Hirnanschwellung” and the posterior the “Seitenanschwellung,” using the terms of
Krieger and Dietl. These latter particulars accord with Reichenbach’s description of the crayfish.
I have not, however, found that in Alpheus, behind the level of the first pair of antennie, the lat-
eral parts (Seitenstriinge) divided up into three sections. Reichenbach further states that in each
segment a middle-strand invagination is found, while the ganglia of the fifth (first maxillary) seg-
ment has a prominent median string.

In Alpheus I find an undoubted median ingrowth of surface ectoblast between the two nerve
cords. This in all probability corresponds to the mittelstrang, and, as already stated, if is most
marked at a stage just before or at the time of the first appearance of the eye pigment, when the
ganglia are separating from the integument. It is seen between the successive segments of the
ventral nerve cord, where a single cell or string of several cells appears to be wedged between the
two cords which are entirely separated (compare Figs. 151, 160). The nuclei of these cells are
elongate and perpendicular with the surface. . They are derived by delamination from the super-
ficial ectoblast, as the karyokinetic figures of dividing cells clearly show. These ingrowths are
most noticeable between the segments, and whether they form any part of the nervous system or
not, I have been unable to determine. In insects the mittelstrang appears to take no part in the
nervous system of the adult, but in the thoracic region it is converted into the chitenous furce.

According to Reichenbach the lower cesophageal ganglion in the crayfish is formed by the
fusion of the ganglia of the fourth (mandibular) to the ninth (third maxillipedal) segments. This
is probably true of Alpheus, as may be inferred from Fig. 196. $e,

With reference to the commissures, Reichenbach states his belief that the transverse commis-
sures originate in the unpaired fiber masses present in each ganglion, while the paired masses
give rise to longitudinal commissures. In Alpheus there appear in successive segments behind
the mouth a pair of punctsubstanz balls, one ball in each single ganglion. ‘These extend forward
and backward, uniting the ganglia into chains and forming the longitudinal commissures. A little
later the transverse commissures are formed by bridging the cords between the points occupied by
the fiber-substance balls in the several ganglia. All these stages can be observed in the embryo
shown in Fig. 139, but all do not appear in the drawing.

The origin of the peripheral nervous system is beset with many difficulties. It is often impossi-
ble to distinguish developing nerves from rudimentary connective tissue and muscle, owing to the
similarity of the nuclei of each. This is less true of muscles, which in some parts of the embryo, as
in the carapace, are clearly distinguishable. In view of this, Reichenbach found it difficult to say
whether the nerves were budded off from the central nervous system, from other ectoderm, or from
wandering mesoderia cells. He thinks, however, that since many structures like the optic gan-
glion, the erystalline cone cells of the retina, etc., are early recognizable, the nervous system is
generally in intimate connection with the other organs. So the appendages, the nervous system,
and the nerves, which at first can not be distinguished from each other, are intimately connected
from the start; so the eye and the ear are never separated from the central nervous system. The
separation of the central nervous system from the skin takes place slowly, and the ectodermal
thickenings in the early stages must conceal the rudiments of nerves and skin elements. It is
difficult, he remarks, to understand the late connection of the midgut with the central nervous
system and the scattered mesoderm cells which form the muscles, but he says, in conclusion :

Bei der Unterschung der wunderbaren Entwicklungserscheinungen in der organischen Welt aber driingt sich
bei tieferer Betrachtung immer wieder der Gedanke auf, dass man schon vom ersten Stadium an einem untrennbaren
Ganzen gegeniibersteht. (54, p. 80.)

This view of the intimate colonial relations of all the cells of the embryo can not be disputed,
since it follows from the common descent of all the somatic cells from the ovum. But the relation
which the embryonic cells bear to each other as the undifferentiated ectoblast to mesoblast must
be of a very different nature from that which exists between muscle fiber and nerve in tie differ-

”

entiated state. It seems more probable that the union of the central nervous system with other

organs by means of nerves is strictly a secondary one, and that the latter arise by budding, as in
vertebrates, from the central ganglia. The only observations which [ have made on the develop-
ment of nerves (see section 1) refer to those of the first and second antennw (Pl. Ly, Figs.
213-216, n. au., n. a. g.; Pl. Lvtl, Fig. 243, n. au.). The antennular nerve, which supplies

444 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ~

the ear, appears to arise as an outgrowth from the antennular fiber mass of the brain (Fig. 248,
af.). It consists of a fibrous portion leading directly from the fiber mass of the brain and of
somewhat flattened, or spindle-shaped nuclei, which penetrate the cortex of nervous cells and are
undoubtedly proliferated from them. Possibly the internal sheath is continued over the growing

nerve.
IX.—THE EYES.

The eyes in Decapods’ consist of a pair of lateral compound eyes, which in the larva are
mounted upon long stalks, a condition usually retained in the adult, and of a median ocellus. In ~
the Alpheus family the compound eyes are nearly sessile and are completely hooded by the cara-
pace. In the larva, however, the eyes are both naked and possess long, movable peduncles (see the
metamorphosis, Pl. xx1). In Alpheus saulcyi the optic stalks are reduced to a mere rudiment, and,
though provided with muscles, they can possess but very slight power of movément. They meet
on the middle line in front of the brain, over the roots of the first pair of antenne. The compound
eyes face forwards and outwards at an angle of 45° with the mesial plane of the body. A median
papilla projects from below the lateral eyes, bearing the pigmented ocellus (Figs. 209, 210, of
larva). Two small hairy tubercles, outgrowths of the integument, occur on the inuer side of the
optie stalk.

Spence Bate (3) says that since the Alphei are frequently found in ooze and muddy bottoms, he
is inclined to think that they burrow more extensively than the common shrimp, and that the
carapace has become modified to protect the eyes on this account. This may be true, but the
Squill, on the other hand, in which the burrowing habit is more characteristic, have undergone

no such modification.
THE MEDIAN EYE.

The median “ nauplius” eye persists in the adult Alpheus, and is probably functional to some
extent as a visual organ. This is represented in Fig. 18, Pl. xxt1, where it is seen as a small
conical papilla, lying between the basal joints of the antennules, and at the roots of the compound
eyes, very close upon the brain. This is the first instance I have noticed of the persistence of the
nauplius eye in the adult.

The general position of the median eye of the first larva of Alpheus saulcyt is seen in Figs.
209 and 210, and the minute structure in Fig. 197. The pigment takes the form of an inverted
Greek capital upsilon (7). There is no lens. A coaguable fluid is present, which is probably
blood plasma. Besides muscle-fibers and pigment-secreting cells, and the integumentary epithe-
lium, these ectodermic nerve end (?) cells, which abound toward the center of the papilla, are
continous backward into the cortical cells of the anterior fiber mass of the brain.

The first trace of the frontal eye which I have noticed occurs in the tenth stage (Fig. 168),
when a small number of cells developing black pigment (probably ectodermic) can be seen near
the surface, on the middle line, next the anterior extremity of the brain.*

GENERAL ANATOMY OF THE EYESTALK.

The visual apparatus of the compound eye of a Crustacean consists ef three principal parts,
the retina, the optic ganglion, and the optic nerve, uniting retina with ganglion, in addition to a
peduncle of nerve fibers, which puts the optic ganglion in communication with the brain. * These
parts are contained in the eyestalk or opthalmite. The eyestalks are covered with a cuticle
secreted by the ectoderm like that over the rest of the body. This cuticle, which in some prawns
like Stenopus is hard and armed with spines, is converted at the distal, hemispherical surface of
the stalk into a transparent cornea. The ectoderm or hypodermis secretes a well defined basement
membrane. This is continuous with the basement membrane of the retina, pointing clearly to the —
fact which development proves, that the retina is a differentiated portion of the hypodermis.
Below the basal membrane we meet with blood vessels or sinuses, muscles which control the
movements of the eyestalk, glands, connective tissue, ganglion cells, and fibrous substance.

* While this memoir was in press a short paper appeared in the Quarterly Journal of Microscopical Science (January,
1892), ‘On the Nauplius Eye persisting in some Decapods.” by Margaret Robinson. The median eye was observed in
some eight different species of the Carididx, including the genera Palwmon, Hippolyte, Virbius, Crangon, and Pan-
dalus.

-

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 445

Alpheus in the only genus in which I have found glands in the eyestalk. These are most notice-
able at the peripheral parts of the stalk between the basement membrane and the ganglia. They
are in reality parts of the green gland, which sends outgrowths from the bases of the second
antenn into the antennules, the eyestalks, the labrum, and the whole frout of the head, so as to

7 completely envelope the brain. The histology ot the glandular coeca is the same in all parts.
They consist of a cubical epithelium, composed of very large cells, supported by a basement mem-
brane.

Near the coeca of the antennal gland comes a layer of very loose connective tissne. This is
specially abundant below the basement membrane of the retina. it forms a continuous sheath
tor the optie ganglion, and is reflected over the optic peduncle and brain.

Xe By far the greater mass of tissues of the eyestalk belongs to the optie ganglion. This is
bi- composed of ganglion cells (ig. 187), nerve fibers, and the peculiar fibrous tissue variously
called “ Punct-substanz” or “ Ball-substanz,” and “substance ponctuée.” Viallanes, who has
made very careful and detailed studies of the optic ganglia of Arthropods, uses the following
terminology (61). He divides the optic ganglion into two parts, an external and an internal
portion. The surface of the external region is covered by the limiting membrane of the eye.
The external is united to the internal parts by a bundle of crossing fibers, the external chi-
asma (Fig. 178, Ch. Ex.). This, according to Viallanes, corresponds to the center of the corneal
surface, and consequently to that of the limiting membrane of the eye. The internal portion
between the external chiasma and the optic peduncle is composed of three principal masses of
punet-substanz: (1) la masse médullaire externe, (2) la masse médullaire interne, (3) la masse
médullaire terminale. The external medullary mass is united to the masse médullaire interne by
an internal chiasma, while a fibrous peduncle joins the internal medullary mass to the masse
-- médullaire terminale. The nerve fibers which pass between retina and ganglion, he calls the post,
retinal fibers, and designates as “ optic nerve” the peduncle by which the optice ganglion is united to
the brain. The distal mass of punct-substanz is styled lame ganglionnaire,* which he divides into
a nuclear layer (couche 4 noyaux), a molecular layer (couche moléculaire), and a cellular layer
(couche a cellules ganglionnaires).
The punct-substanz of the optic ganglion is thus divided into four principal masses (Figs. 178,
209). Without adhering closely to the rather cumbrous terminology of Viallanes, the parts of the
nervous system contained in the eyestalk between the brain and retina may be designated as
follows: Optic peduncle (optic nerve of Viallanes and others); proximal segment (masse médullaire
terminale); internal middle segment (masse médullaire interne); external middle segment (masse
5 médullaire externe); distal segment (lame ganglionnaire); optic nerve (couche des fibers post-
rétiniennes).
GENERAL STRUCTURE OF THE COMPOUND EYE.

; The transparent cornea is the secreted product of a specialized layer of the hypodermis, which
was designated by Patten as the “corneal hypodermis” and later as thé ‘‘ corneagen” (50, 51).
Beneath this lie several strata of dioptic and sensory cells, separated from the ganglion by a base-
ment membrane, which is continuous with that of the general hypodermis of the eyestalk. The
ommateum, or eye proper (including those parts which intervene between the cornea and basal
membrane), is formed by the repetition of a highly specialized unit, the eyelet or ommatidium. The
size, number, and arrangement of the ommatidia is characteristic of species or genera, but is subject
to considerable variation in different individuals, and the shape and arrangement of the ommatidia

~ — may be very irregular in different parts of the same eye. The ommatidia are differentiated clusters
of ectoderm cells. There is a single ommatidium for each lens or corneal facet. The number of
cells composing the ommatidium is very uniform in Decapods, Stomatopods, and Schizopods, so far
at least, as the most essential cells are concerned. They are as follows: Cells of corneal hypo-
dermis, 2; crystalline-cone cells, 4; outer pigmented retinular cells, 2; inner pigmented retinular
cells, 7 (functional); Accessory pigmented cells—irregularly distributed, both above and below
the basement membrane, probably of ectodermie origin.

* The lame ganglionnaire is called ‘Retina ganglion” by Claus, who regards it as the true retina; ‘das aussere
Ganglion opticum” by Carriere, and “ periopticum” by Hickson.

Me
+9

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yore sy

446 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

a)

ee

STRUCTURE OF THE* OMMATIDIUM,

*
*

Both a lack of time and of fresh material have prevented me from making as thorough a study
of the structure of the ommatidium of Alpheus as I had wished. The following account is based
entirely upon sections :

The corneal facet is strongly biconvex (Fig. 200), the convexity of the lower side being the
greatest. Its shape is usually hexagonal, but may be tetragonal, or sometimes nearly cireular
(as in A. heterochelis). There are two corneal cells to each lens. A single ommatidium is shown
in Fig. 200. As in all Decapods, the cone cells which underlie the corneagen are tour in number.
The four segments of the crystalline cone (Fig. 208), which are secreted on the inner sides of the
latter cells, are always separated by delicate boundary lines. The cone is capped by amass of
protoplasm in which the uuclei of the cone cells lie, although it is not always easy to distinguish
them. This cap appears to be raised into a slight elevation which touches the center of the lens.

Pigment cells invest the cone more or less completely according to the conditions under which
the eye is examined. These are the retinular cells. In the larva, and probably in the adult also,
there are two distal retinular cells (pg. ¢ PJ. Liv), as Parker (48) designates them, and at least
seven proximal retinular cells (rél.). Parker discovered in Homarus and several allied forms
a rudimentary eighth cell belonging to the proximal series. This is present I believe, in Alpheus,
although my sections do not show it with the same clearness that it can be demonstrated in Pale-
monetes. The seven proximal retinular cells secrete on their inner sides the rhabdom or rhab-
domeres. A transverse section of the rhabdom gives the peculiar seven-pronged figure shown in
the drawing (Fig. 205). The cells appear as fused in section, but possibly they would separate
with readiness if macerated. Unfortunately I had no fresh material to experiment with. The
proximal retinular cells appear to penetrate the basement membrane, and they are continuous
below it with nerve fibrils. As to their distal ends, I have seen no evidence that they extend out
to meet the cornea. ‘The retinular cells abound in dark pigment.

The accessory pigment cells secrete a peculiar pigment which is glistening white in reflected
light and is amber color in transmitted light. This may be similar to the pigment of certain cells
which occur beneath the cuticle of the larva of Decapods in various parts of the body. It is not
décolorized when subject to the prolonged action of weak solutions of nitric acid, while the black
pigment is completely removed. What I once regarded as chitinous bodies (20-21) were fused
masses of this pigment which had been treated with nitrié acid. These cells penetrate the base-
ment membrane, beneath which there is a considerable mass of both yellow and black pigment.
The trains of celis which accompany nerve fibrils into the fibrous portions of the optic ganglia also
contain granules of black pigment. The number of accessory pigment cells belonging to each
ommatidium is indeterminate. They have the power of free movement or migration outward from
the basement membrane and the power of retraction like the retinular cells. In Fig. 200 they are
seen widely diffused, while there is a zone of black pigment cells (the pigment withdrawn by acid)
enveloping nearly the entire cone and the distal end of the rhabdom. In an eye taken from a prawn
which had just moulted, the yellow pigment was restricted to a narrow zone next the basement
membrane. Outside of this belt the retinular cells were colorless nearly up to the proximal ends
- of the cones, while the cones themselves were draped in black.

Lee RES kate ea eT

ARRANGEMENT OF THE OMMATIDIA.

,

In Alpheus sauleyi the ommatidia are arranged in a hexagonal system, subject to variations
in different parts of the eye.* In the central parts of the cornea the facets are symmetrical hexa-
gons. On the lower side of the eye the rows are more irregular and individual facets tend to
become square and rounded. ‘Toward the outer side of the eye the facets are very nearly square,
next to these they become irregular and rounded, and on the extreme outer edge the facets are
sometimes hexagonal. There is probably considerable individual variation. 1 bave examined the
cornea in four other species of Alpheus, namely in Alpheus heterochelis, A. minor, A. normani, and
a West Indian species closely allied to A. heterochelis. These cases afford some very interesting —

* For a study of the cornea, adults of the largest size were selected and the cuticle was cleaned by boiling in a
concentrated solution of potassic hydrate.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 447

facts in connection with the arrangement of ommatidia. In Alpheus normani the facets are gen-
erally symmetrical hexagons, two of the sides being quite short. These tend to run into squares
or rounded areas at parts of the periphery. Alpheus minor has the facets in the lower part of the
eye either of the hexagonal or some polygonal form, while in the upper and outer parts the facets
are perfect squares. These blend on all sides into symmetrical hexagons. The first transition
from the hexagon to the square is seen on the outer edges of this‘area where the individual facets
become more and more rhomboidal, as the two opposite sides of the hexagon are more and more
reduced. Finally these sides disappear and the facets become rectangular. The square facets of
any given row now lie opposite to those of the adjoining rows. Four facets belonging to any two
rows meet at a common point. In passing, however, from the area of square facets to the periph-
eral parts, the facets, though square, are out of line. Starting from a point where the facets of a
given row are both tetragonal and opposite those of adjoining rows, and following the line over
the hemispherical surface toward the periphery, the facets of this row soon tend to become alter-
nate with those of the row next toit. A facet of the second row lies slightly in front of the cor-

‘responding facet of the first row. The facet of the third row lies a little in advance of this and so
on until the hexagonal shape is gradually assumed.

In the Bahaman variety of Alpheus heterochelis the facets in the larval eye are markedly hex-
agonal. In the adult there is the same curious transition from the hexagon to the square as we
have noticed in Alpheus minor, only it is here much more striking. In the peripheral parts of the
eye, especially in the lower and inner portions, the facets are generally hexagonal. In the upper
half of the eye between the center and periphery there is a small area of square facets. In Alpheus
heterochelis the fac.ts are characterized by much greater looseness of arrangement, there being
large interlenticular spaces. The facets are squares with ronnded corners. In some parts of the
eye, as on the inner lower side, the facets of the adjoining rows lie opposite each other. In other
parts they regularly alternate and show a tendency to become hexagonal. At the periphery the
facets are widely separated and circular.*

The markings on the corneal lenses generally consist of a small central spot which is slightly
elongated and strongly refracts the light. It appears in section to represent a slight depression.
In the lobster, as first shown by Parker, there is a faint diagonal band which intersects a central
hazy spot and divides the square into equal triangles. These diagonal bands are all parallel in
adjoining rows. In Alpheus saulcyi the elongated spots, if continued across the lens, would form
a series of similar diagonal lines, but none such as these could be detected. . In Alpheus heterochelis
the markings are very constant and peculiar. In the center of the lens there is a large irregular
impression from which numerous rays extend on ali sides. The latter do not always reach the
periphery. They appear like grooves in the substance of the lens. In the older embryo (Fig. 194)
the apex of the cone cells seems to touch the under side of the lens in certain parts of the eye. It
is therefore possible that these cells remain in contact with the cornea and the interference thus
caused gives rise to the spot. A similar explanation is offered by Parker to account for the con-
ditions found in the lobster. The significance of the radiating lines seen in Alpheus heterochelis I
have not determined. ,

In Homarus the facets are square and grouped with remarkable regularity up to the very
edge of the cornea, excepting at a point on the upper side, where a peninsula of tough cuticle juts
in from the surface of the stalk and interrupts the elliptical jet black area of the surface of the
eye. About this process, particularly in front of it, the facets are hexagonal or irregular and very
much smaller.

Parker (48) states that in the lobster “the ommatidia rearrange themselves between the times
when the young animal is 1 inch and 8 inches long. During this period the ommatidia increase
about ten times in length and about five times in breadth.” I find that this rearrangement begins
at a much earlier period, in fact in the older larval stages. My examination comprised the follow-
ing stages: (1) Length 8-9™™ (first larval stage); (2) length 11™™ (fourth larva); (3) length 15.3"™™"
(sixth larval stage); (4) length 49™™ (lobster 1 year old). ~

*A similar transition of the square into the hexagonal facet in the same eye occurs in Astacus. See Howes’
Biological Atlas, Fig. 111. -

448 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

In the first larva of both Homarus and Alpheus sauleyi I find that the facets are not only hex-
agonal but tend aiso to be slightly rounded. In the larva 11™ long the lenses tend to become
square toward the center of the cornea, while at the periphery they are smaller and generally hex-
agonal. Occasionally, however (just in what part I did not ascertain), the peripheral facets tend
strongly to the tetragonal arrangement. In the next case (larva 15.3"™ long) the facets in the
outer parts of the eye are small and symmetrical hexagons. Toward the center they become
larger, nearly square, and there is considerable interlenticular space.

In the yearling lobster the readjustment of the corneal lenses from the hexagonal to the tetrag-
onal system has been effected over the greater portion of the eye, but the transition is still illus-
trated ina very beautiful manner. The cuticular ingrowth or peninsula, already referred to, seen at
the upper surface, is hook-shaped, bending backward. In the open angle in front the retina is least
ditferentiated. The corneal facets in this region are small and mostly hexagonal. Following the
lines of facets as they curve outward and backward from this point over the convex surface of the
eye, we see illustrated in a very striking way the passage of the hexagon into the square by the
gradual reduction of the opposite sides. The sides which are sacrificed are the third and sixth,
counting from the side which hes between two adjoining lenses of the same row. Over a consid-
erable area the facets are not quite square and thus tend to alternate with those of adjoining rows.
The gradual transitiou to the square is attended by a gradual increase in size. In the narrow
angle behind the peninsula, the area of the hexagonal facets is smaller. In all other parts of the
periphery the facets are square up to the very edge, as in the adult. The corneal lens in an 8-inch
lobster has about twice the area of that of the lobster one year old (length nearly 2 inches).

After reviewing these details the difficult question arises: What is the significance of this
remarkable change, and how is it effected ?

Parker (48), who has made a careful study of the arrangement of the ommatidia in different
Crustaceans, recognizes two plans on which these organs are grouped, the hexagonal and the tetrag-
onal. He says that ‘in the Brachyura, as well as in three families of the Macrura, the Hippide,
Paguride, and Thalassinide, the arrangement of the ommatidia is invariably hexagonal. In the
remaining macrurous Decapods the ommatidia are grouped on the tetragonal plan.” There are,
however, exceptions to the latter statement, some of which are mentioned. He regards the change
from the hexagonal to the tetragonal system as apparently due to the increase iu size and the con-
sequent crowding of the ommatidia, and reaches the conclusion trom the various facts presented,
that the hexagonal arrangement is phylogenetically the oldest. Upon this view we should expect
to find the eyes of the most highly differentiated of the Crustacea arranged on the tetragonal sys-
tem, whereas in points of fact the crabs, who are notorious for their great activity aud keen powers
of vision, permanently adopt the hexagonal arrangement. The lower Macrura adopt both methods,
and in certain species of Alpheus, as Alpheus minor, which are active in habit and show no trace of
degeneracy, the change is begun but not completed in the same retina. In order of time the hex-
agonal prism precedes the square prism and the conditions which determine the permanency of
each of these systems in the adult life of the individual are undoubtedly inherited, but they do not
appear to have a phylogenetic significance, at least I do not see the way clear to au explanation
upon this ground.

Taking, for example, the lobster and the crab, in each case the larval eye represents, we must
believe, the more generalized type, the adult eye the more specialized type. The larval eye of both
Macrouran and Brachyouran has the hexagonal facet. We may safely conclude that this is a
primitive arrangement. The adult crab, which has a more highly organized nervous system and
keener senses, retains this primitive arrangement, while the lobster, whose seuses are without
doubt duller, departs from the type, and in the adult the facets of the cornea take on a permanent
tetragonal shape. The conditions which we would naturally look for are thus reversed in these
two forms. 3 ;

We must assume that the change in the case of the lobster is a useful variation, that it is in
some way subservient to keen vision, otherwise it could never, upon the theory of natural selection,
have secured such a permanent characteristic footing. On the other hand we must believe that
the hexagonal facet puts the eye of the crab into better harmony with its environment than the
square facet would do, for if the eye had not been in harmony with external conditions it must

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 449

have varied and attained to a new structure during the course of the evolution of the Brachyoura
from Macrouran ancestors.

Many crabs like the sand crab, Ocypoda arenaria, spend a good portion of time out of
the water and their eyes are admirably adapted for vision in the air, as in the case of this species,
which will detect any moving object, such as a man or a dog, a long distance off. We might thus
hope to find a way of escape trom the difficulty in the diversity of habits in the two forms, the
lobster being exclusively an aquatic animal. But the primitive Crustacea must have all been
aquatic, and the hermit crabs, some of which spend all or nearly all of their time in the water,
agree with the Brachyoura in having a corneal membrane composed of hexagonal facets, not to
speak of other Macrouran forms which are invariably aquatic, like Alpheus, in which the hexagonal
system is retained or there is a transitional condition between the hexagon and the square in the
eye of the adult.

We do not yet know the physical or physiological significance of these two kinds of facets,
and possibly in this fact lies the root of the difficulty pointed out above.

The hexagonal arrangement is the natural ove for tubes with elastic walls to assume when
there is sufficient mutual pressure, and it is also the most economical arrangement, so far as wall
space is concerned, for regular prisms of equal capacity. Next to this in poiut of economy of wall
space comes the square prism, and next to this the triangular prism, where, as before, all available
space is occupied. This last arrangement, however, is not regularly assumed.

lf a given number of hexagonal prisms occupying a given space tend to increase in size, then
they would tend also to assume another form less economical of wall space, such as the square
prism. If the wall area of the hexagonal prism remains the same and the number of prisms
increases in a given space, then each prism must be less economical of wall area and assume
another form like that of the square prism.

If we may apply the same principles to the growing ommatidia, it is possible that crowding
may have something to do with the chauge.

In the lobster the change from the hexagonal to the tetragonal system is attended by a growth
of the ommatidium in all directions and by the addition of new ommatidia. If an outline drawing
of the eye of the first larva of the lobster be compared with a similar one of the fifth larva, it will
be seen that the convexity of the outer surface, that is, the area of the eye, has very greatly
increased, whereas the diameter of the eye stalk has remained very nearly the same. During
this period the change from the hexagon to the square has been begun. During this time the

ommatidia have increased in length with the increasing convexity of the cornea, and they have also

increased in sectional area and in actual number. It is a very uoticeable fact also that in the
lobster the eye stalk is compressed dorso-ventrally, so that the horizontal radius of curvature
of the retinal surface is considerably greater than the vertical radius of curvature. Furthermore,
the sides of the hexagonal facets which suffer reduction lie in a vertical plane, indicating a strain
or pressure in a dorso-ventral direction.

In Alpheus sauléyi the relative increase in the convexity of the corneal cuticula is very slight
in passing from the first larva (length, about 4”™™) to later stages, and the eye of an adult (15"™
long) is only about one-fourth larger than that of the larva at the time of hatching. Moreover, in
Alpheus the convex surface of the eye is nearly a perfect hemisphere, the curvatures being the
same in every plane.

If we examine the eyes of a crab in a similar way we find that the area of the surface of the
retina increases less rapidly in passing from the zoéa to the megalops stage than iu the case of
the lobster in going from the first to the fourth larval forms. The comparison, however, is of little
value since the lobster has an abbreviated development. The eye stalk of the adult crab presents
a large retinal surface, but if preserves a nearly cylindrical form, although the radii of curvature of
the retinal surface are very unequal. In the hermit crab (in a single species examined) the hexag-
onal arrangement is preserved, not, however, without indications of a tendency to become tetrag-
onal, the hexagons becoming asymmetrical in certain parts of the eye. There is, however, the
same compression of the eye stalk in a dorso-ventral plane as we see in the lobster.

~ It has seemed to me worth while to point out these facts as offering some suggestions to the
problems under discussion, although I make no attempt at a mechanical explanation.
S. Mis. 94 29

450 MEMOIRS OF THE NATIONAL ACADEMY OF SOIENCES.

The primitive arrangement of the ommatidia was probably in the form of simple tubes or
cylinders, with spaces between them and with rounded or indefinite facets. Mutual pressure
among these tubular eyelets, arising from any cause, produces the hexagonal arrangement, the
most economical method so far as wall space is concerned. Interferences such as have been sug-
gested, as growth of individual ommatidia or increase in the number of ommatidia in the same
area, thus admitting a method of arrangement less economical of wall space, or the great increase
in length of the ommatidia and a relatively less increase in width, attended by a progressive change
of the hexagons into squares (the apparent slipping of the rows of facets on one another), may
euter as factors into this change, but they do not suffice to explain all the conditions. It will be
understood, of course, that there are no changes in the individual facets, these remaining in the
same shape until they are cast off in the moult. The changes which the individual ommatidia
undergo are very gradual, and since the number of cells for each ommatidium is constant and deter-
mined at avery early period, excepting the accessory pigment cells, they must be attributed to
the change in the size and relative positions of the cells themselves rather than to intussusception.
It is possible that the change from the hexagon to the square is not produced in the same way in
all cases and that the conditions of growth which bring about this result are far more compli-
eated than would appear from the suggestions which have been made. A careful study of the
arrangement of cells in the ommatidia of the eye of the young lobster during the period of transi-
tion would possibly throw some light upon this interesting subject.

THE DEVELOPMENT OF THE COMPOUND EYE,

Five years ago (20) I stated my conviction that the compound eye of Alpheus, and probably
also of Palzmontes and of the large Isopod, Ligea oceanica, originated from a thickening of the
superficial ectoblast. The development of the eye in Alpheus was more fully described in a pre-
liminary notice (21). I will now recapitulate the main results, at the same time correcting such
errors as I have detected.

In studying the development of the eye the following are some of the subjects which present
themselves for investigation: The origin and structure of the optic disks; the separation of the
optic disks into a ganglionic and retinal portion by an intercepting basement membrane; the dif-
ferentiation of the retina into ommatidia or eyelets; the differentiation of the optic ganglion and
the development of the optic nerve, by means of which the sensory end organs of the retina come
in direct relation with the ganglion.

(1) Origin of the Optic Disk.—The optic disks (Fig. 58, Pl. xxx11) consist of large ectodermic
areas or patches on either side of the middle line. They are centers of rapid cell division, united
by means of the lateral cords, which are bands of proliferating cells, with the thoracic-abdominal
plate.

So far as I am aware we have no account of the origin of the optic disk in any Decapod except-
ing Alpheus, Astacus (54), Crangon (30), and Homarus (47... Parker, in his careful studies on the
eye of the lobster, was unable to obtain the earliest traces of the developing optic disk, and the
accounts of Reichenbach and Kingsley differ very materially. I will therefore describe somewhat
in detail the process by which the optic disk is produced in Alpheus.

The optic disks at the time when they consist of a single stratum of cells are shown in Figs.
58, 68, and 69. A series of four transverse sections through the central portion of the left optic
disk is represented in Figs. 64-67. The posterior face of each section is presented, the series pass-
ing from the front backward.

Since it is from the optic disk that the eye and its ganglion are developed, the important inquiry
which arises at this stage is, how is the change effected by which the disk passes from this single-
layered to a many-layered condition like that seen in the egg nauplius (Figs. 107, 114)? If the
eye represents a series of hypodermal pits, it would be reasonable to look for some trace of these
infoldiugs in the embryo. If, on the other hand, the compound eye of the higher Crustacea repre-
sents a closed vesicle produced by a single invagination of the hypodermis, of the type seen in the
prototracheate Peripatus, we should expect to find some trace of an involution at this stage. So the
answer to this question may have an important bearing upon the phylogeny of the compound eye.

Cell boundaries are easily discernible at the surface, but it is evident that the nuclei donot

.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 451

all lie at the same level. Passing now to Stage rv (Fig. 72), we notice several important changes
in the external appearance of the optic disks. They have approached nearer the middle line;
they have increased in area; their nuclei are more crowded; near the center of the disk and on
the side of it toward the middle line (Fig. 72, C. M.) the nuclei are distinctly larger. In inter-
preting these changes we must resort to sections and a careful study of dividing nuclei. A com-
plete series of consecutive transverse sections through the: left optic disk at this critical stage is
given in Pl, xxxv. The last of the series cuts the rudiment of the first antenna. Karyokinetic
figures come to our aid in pointing out the way in which the growth of the disk is effected. The
nuclei divide either radially, the plane of division, clearly marked by the equatorial plate, being
perpendicular to the surface, or horizontally, the plate being in this case parallel with the
surface. In a single disk at this stage there were eight cells undergoing radial division. Of
these, six were near the periphery, where the cells formed a single stratum, while two were near
the center, where the disk was slightly thickened (Fig. 80, OC. W/.). It is evident from this and
similar cases that the increase in area of the disk is accomplished by radial cell division, The
same is true of all proliferating areas in the lateral cords, where the appendages are soon budded.

In the area marked C. Jf. (Fig. 80) the optic disk is no longer a single layer. This thickening
is due either to horizontal cell division, that is, delamination, or to emigration. The appearances
of emigration are often very deceitful, but I think we may safely conclude that the initial thick-
ening of the optic disk in the proliferating area, marked C. M. (Figs. 80, 90), is due to emigration,
that a solid ingrowth akin to invagination takes place at this point. Thus the cell marked ec in
Fig. 80 is distinctly below the surface. The boundaries of the cell can be clearly seen. The cell
ec in Fig. 90 (dotted line should be extended), on the other hand, is clearly in contact with the
surface by a slender protoplasmic process, while the nucleus lies at a much lower level. I inter-
pret the latter as a cell at the point of breaking all connection with the surface and migrating toa
lower position. In the first instance this has already been accomplished.

In the stages under discussion there are one or two cases out of a large number of sections
involving the optic disks of several individuals, which probably indicate delamination in the
peripheral parts. Ata later period (Figs. 102-107) the nuclear figures are conclusive. In one
instance (Fig. 102, ec.) two cells are seen delaminating side by side. The thickening of the optie
disk is thus due in part to delamination, apd this process is probably supplemented by emigration,
at least in the central area. The central area represents in all probability the “ optic invagination”
of the crayfish, and is concerned solely with the production of the optic ganglion. In Alpheus
there is a proliferating area simply, but no superficial depression or invagination in the strict
sense.

It is noticeable that in Stage it (Pl. xxx1m) wandering cells, or cells which travel through the
yolk, have not appeared in the neighborhood of the optic disks. In Stage rv (Fig. 70, Y. C.) they are
not far away, and in later stages (Fig. 91) these cells are close upon the disks. Some ot them which
enter this region, coming near to or uniting with the disks, undoubtedly degenerate (compare Y. C.,
Fig. 94, s—s', Figs. 95, 96,99, 100). Some of the cells of the disks next the yolk elongate, and appear
to form a somewhat transitory covering. As already suggested, these bodies are probably derived
from the wandering cells.

The various stages by which the disk, already described, is converted into a conspicuous,
lobular mass of cells in closest relation with the antennular ganglion such as we have in the egg-
nauplius (Fig. 111, 0. Z), can be seen by reference to the plates (Pls. XxXVI-XL).

(2) The Development of the Retina and Optic Ganglion.—The next event of importance is the
differentiation of the optic disk into ganglionic and retinal portions. This is already begun in
Stage vu. A deeper layer from which the ganglion is developed (Figs. 129, 132, @. L.) is gradually
separated from a superficial tier of cells with very large nuclei (OZ). This layer is the retinogen.
The differentiation begins in the lateral lower halves of the optic disks and extends upwards and
toward the middle line. As the disk spreads outwards, and at the same time increases in thick-
ness, it tends to overgrow the hypodermis and becomes raised into a lobe or fold. The optic lobe
(Figs. 136, 138) thus represents a thickening of the hypodermis. It is covered next the yolk by a
delicate basement membrane (Bm.), which is continvons with that of the surrounding hypodermis.

452 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Wandering cells are seen in contact with this membrane (Fig. 136), but they probably do not
share in its secretion, although they occur in the closest relations with it.

At a little later period (Fig. 138) the retinal portion is several cells thick on the outer edges
of the lobe, while it is a single stratum in the sagittal section, shown in Fig. 158. The plane of

section is near the center of the lobe. The deeper nuclei of the ganglion are large and clear, the ~

outer are Smaller and stain more intensely. This section can be clearly understood if compared
with the transverse section, Fig. 146. We see that the optic ganglion is here divided into an
external or distal part and an internal or proximal portion by a thin sheet of very large and clear
ganglion cells. Parker (47) describes and figures an exactly similar structure in the lobster, and
I fully agree with him in regarding this band of nuclei as representing similar bands, which
Reichenbach (Taf. x11, Figs. 173, 174, A. W. 7. W.) describes in the crayfish. In Reichenbach’s
plates these uuclei appear as a narrow fold, forming the lining of what is described as a secondary
optic invagination. y

Three punct-substanz masses have already appeared in the inner half of the optic ganglion,
the external middle segment, which lies next to the band of large nuclei, and the internal middle
and proximal segments. The proximal medullary mass is much the largest and is the first to be
differentiated, although the others follow close upon it. The dividing nuclear band lasts but a
short time, and in Stage 10 (Fig. 167) has disappeared. In front of it is developed the lame gang-
lionaire or distal segment of the optic ganglion. This has an outer convex surface which is con-
centric with the basal membrane and with the outer surface of the retina, and it is carpeted by a
special layer of ectoderm cells. These appear in section as a single row of elongated nuclei.

Jn an early communication (20) I stated my belief that the punct-substanz arose from a
metamorphosis of ganglion cells. This view was suggested by certain appearances presented
by the large clear nuclei, more particularly by those of the dividing band in the optie glanglion
(see Fig. 180). Kingsley (32),came to the same conclusion in regard to certain large clear nuclei
in or near the distal segment of the optic ganglion of Crangon. In reviewing this subject more
earefully I am convinced that this interpretation is erroneous. These large clear cells are in
reality undergoing indirect cell division, as proved by the karyokinetice figures which are occa-
sionally seen. Both the chromatin network and the chromosomes are exceedingly delicate, and
when the section is in the plane of the equatorial plate an appearance is presented which under
certain conditions of staining and preparation might easily be interpreted in favor of retrogressive
metamorphosis. I conclude that the punct-substanz of the nervous centers is in all cases derived
from the protoplasm of cells, not from cell nuclei.

In Stage 1x when eye pigment first appears, the structure of the retina is very simple. By
the transverse section (Fig. 146), we see that the retina consists of a thickened ectoderm plate,
thickest in its deeper portions, thinning out toward the middle line at the surface. It has the
shape of the half section of a concavo-convex lens.

In Palemonetes the structure of the eye is precisely similar at this stage. Fig. 189 gives a
section of the eye of this prawn, on a line with the cesophagus behind the optic ganglion, where
it is seen to rest against the yolk. The black pigment, though appearing to arise in connection
with certain mesodermie cells (wandering cells from the yolk), itin reality belongs to deep ectoderm,
, and marks the retinular cells. The cell protoplasm bearing the pigment bodies grows outward
(Fig. 146), and also pierces and extends some distance below the basement membrane (Figs. 191,
192). The latter is a delicate cuticular structure secreted by the ectoderm cells which lie along
the line of division of retina and ganglion, aud continuous with the basement membrane of the
hypodermis. In some sections it appears to be duplex, a coudition described for the eye of
the lobster by Parker (47), in which the inner layer enfolds the optic ganglion. The wide open
fissure which now exists between retina and ganglion (seen in transverse section at an, Fig. 136)
is partially filled with yolk. There is not the slightest doubt that cells enter this fissure from
the yolk (Mes. Figs. 146, 167, 189, 194, etc.), but what the fate of these wandering bodies is, I find
it very difficult to decide. IL think, however, that it can be stated definitely that none of these
cells enter the retinogen. They must supply some of the pigment found in this region, or they
may become converted into connective tissue. In Stage x (Fig. 167) the yellow accessory pig-
ment cells are clearly differentiated, or at least the pigment which these bodies give rise to, is seen

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 453

in abundance around the retinular elements. This is without doubt ectodermic in origin. Some
yellow pigment also occurs below the basement membrane. This may be ectodermic or meso-
dermic, but the great bulk, if not all the accessory pigment cells, which in the adult eye extend
their processes through the basement membrane, are ectodermic in their origin.

At the edge of the retinal plate the cells become very much elongated (Figs. 146, 188), aud
finaily can no longer be distinguished from the superficial ectoderm. The thickening of the retinal
plate is due solely to emigration. This might be inferred by the interwedging of the nuclei (Figs.
188, 189), and it is proved in cases of cell division by the position of the equatorial plate, which is
always perpendicular to the surface.*

A later stage in the development of the eye is illustrated by Figs. 190 and 191, which are
anterior (superficial) and posterior (deep) transverse sections. In Fig. 190 we see the retina differ-
entiated into cell clusters. Each cluster represents part of an ommatidium—the corneal hypo-
dermis, the cone cells, and possibly the distal retinular cells. The lower stratum of small nuclei
belongs to the proximal retinulze and to the accessory pigment cells. In deeper section, Fig. 191,
we distinguish the proximal retinule—black, rod-shaped bodies piercing the basal membrane.
The nuclei lie at the distal extremity of the pigment. Between the pigmented parts of the retinular
cells other nuclei occur, which possibly represent an eighth rudimentary retinular cell (rél’), Atthe
surface of the eye there is a stratum of cells with elongated nuclei. These are the nuclei of the cor-
neal cells and probably also of the distal retinule. Between this and the inner stratum of retinular
nuclei, the nuclei of the cone cells are seen, and a granular substance which is probably the first
trace of the peculiar secretion of these cells. In an older stage represented by the drawing (Fig.
192) we see all these parts in a higher degree of development, and the eye has grown out into a
very prominent lobe. Fig. 167 is intermediate between this and Fig. 191. The central parts of
this eye are the most highly developed, and as we pass to the periphery especially away from the
middle line, the ommatidia are less and less developed, until they reach the condition of a single
layer of undifferentiated ectoderm. Thus, in a single section (like Fig. 192), we have a sort of com-
posite picture of the various stages through which the developing retina has passed.

A considerably older stage is reached in Fig. 194. The cells of the corneal hypodermis are
quite large and have already secreted a cuticular lens. The nuclei of the cone-mother cells are
also conspicuous.

Later still, when the embryo is nearly ready to hatch, the eye has undergone very slight
change. Fig. 187 represents an oblique longitudinal section through the eye stalk of Alpheus
heterochelis. The black pigment of the retinular cells has been removed by the action of the nitric
acid. Irregular sheets and masses of yellow pigment oceur both above and below the basement
membrane. The conspicuous stratum of nuclei, in which the bases of the cone cells are embedded,
belong to the proximal retinular cells. The nuclei (unrepresented) lie close to the surface between
the corneal cells. The cone cells end distally in a conical cap of protoplasm, the apex of which
touches, in some cases at least, the corneal facet. The proximal ends of the cont cells taper grada-
ally and can not be traced below the pigment zone.

In the first larva of Alpheus saulcyi the structure of the eye is similar. This is illustrated in
Figs. 201-204 and Fig. 209. In transverse section (Fig. 201) the corneal cells are crescent-shaped.
The distal retinule lie in the same plane with the latter and have the peculiar arrangement shown
in the drawing. They are grouped in pairs, so that each set of corneal cells is surrounded by
six nuclei—two pairs of nuclei and twosingle nuclei. The two odd nuclei pertain to the omma-
tidium in question. The delicate membranes which appear to surround the corneal cells belong,
in all probability, to the distal retinular cells.

The structure of the compound eye has become a favorite subject of research during the past
five years, and the important study of the development of the faceted eye, about which very little
was known when Balfour’s ‘Comparative Embryology” appeared, has not been neglected; still
much work needs yet to be done in this direction. The literature of this subject has been recently
examined by Parker (48), and I will therefore add to this account only a few comparative notes.

* Parker states that the corneal hypodermis arises in the lobster by simple delamination. (Op. cit.) I have
never seen delaminating cells in any part of the retina of Alpheus or Palwmonetes.

454 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

The proliferating areas in the optic disks of Alpheus and Homarus are undoubtedly homologous,
and probably correspond also to the optic invaginations described in Astacus by Reichenbach and
in Crangon by Kingsley. I therefore agree with Parker (47) in interpreting the ingrowth or invo-
lution of ectoderm, whichever may occur in the developing disk, as concerned with the optic gan-
glion solely and not with the retina, Reichenbach describes the visual organs as originating from
three factors: (1) an epidermal layer; (2) the optic invagination; (3) the optic or segmental
ganglion. From the epidermal layer and outer wall of the optic invagination the retina arises,
while the inner wall of the secondary invagination unites with the optic ganglion. An inspection
of Reichenbach’s Fig. 224 (54) shows, as Parker has pointed out, that in all probability Reichen-
bach has misinterpreted his sections, aud that the entire retina is derived from the bypodermal
layer. The layer of cells with elongated nuclei, which he has designated as rhabdom, clearly per-
tains to the optic ganglion, and probably represents the nuclear covering of the distal convex
surface of the lame ganglionaire (Fig. 192 of this work).

Kingsley, in his third paper on Crangon, changes his interpretation of the invagination of the
optie disk of Crangon, regarding this involution as concerned only with the optic ganglion. I am
inclined to believe that a renewed study of this subject would show that the optic disk originates
in Crangon precisely as it does in Alpheus. <A series of sections through the thickening disk of
Crangon has little to show which is not brought out by a similar series of Alpheus (Figs. 76-83),
and no pit or hollow invagination is seen.

The independent origin of the optic ganglia lends some support to the view that they have a
segmental value and are not merely outgrowths from the brain, that the eyestalk is a modified
appendage containing its proper ganglia.

Watase’s interesting views (63) concerning the origin of the ommatidium an a hypodermal
pit do not receive the support we should expect from embryology. How much value is to be given
to the embryological data in this case it is hard to say, but, seeing the persistence of the involu-
tions in the eye of Limulus, we would expect to find a trace of similar infoldings in the developing
eye of the lower Crustacea, provided their eyes are constructed upon the same type. Until greater
evidence is furnished I am inclined to regard the “compound eye” not as an aggregate of simple
eyes, as the name implies, each one of which is due to a hypodermal infolding, but rather, as Par-
ker has suggested, to differentiated clusters of ectoderm cells originating from a single epithelial
layer.

THE EYE UNDER THE INFLUENCE OF LIGHT AND DARKNESS.

In June, 1890, while enjoying the facilities for biological research afforded by the labora-
tory of the U. 8S. Fish Commission at Woods Holl, Mass., it occurred to me that some valuable
experiments could be made by testing the effects of direct sunlight and total darkness upon the
growth and behavior of the pigment cells of the compound eye of Crustacea. After finishing my
experiments upon one form I learned of the experimental work of Exner* upon the eyes of the
glowworm, Lampyris splendidula, of Hydrophilus, Dysticus, and Colymbetes, in which he records
the same phenomenon in insects which I have observed in a Crustacean. Later a paper has also
appeared, by Mademoiselle M. Stephanowska, on the histological arrangement of pigment in the
eye of Arthropods. I have seen only an abstract of this work, from which I gather that it deals
either largely or entirely with the eyes of insects. My experiments were made upon the common
prawn, Palemonetes vulgaris.

A dark chamber was constructed and rendered as absolutely light-proof as possible. Inside
of this a small glass aquarium was so arranged that a stream of sea water could be kept run-
ning through it for any length of time. Three egg-bearing females were then placed in the
aquarium and the chamber was sealed. The egg embryos were early nauplius stages. Jemales
with eggs in a similar stage were also kept under observation in an aquarium exposed to the light.
_ The general cast of color of the prawn taken in the light is some shade of light brown or brownish
green. After spending eighteen days in the dark, the prawns were taken out and exposed to the
moderately bright Neale of the Gesu te.” The eyes were jet black and appeared to have greatly

% eae ese notes were written I have’ pe ‘the completed work of Exner, Die Physiologie der Facettirten
Augen von Krebsen und Insecten, in which the field of experiment is greatly enlarged.

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 455

swelled in size, and the body was bleached nearly white. The peculiar appearance of the eyes was
caused by the forward extension of the distal retinular cells, of which there is a single pair in each
ommatidium.

' The eggs of some of the prawns were hatching, and the pigment of the zoéa was carefully

/ compared with that of the first larva of Palemonetes hatched in the light. Both the black pigment
of the retinular cells and the yellowish green pigment of the accessory pigment cells of the eye
and the large brown chromatophores in different parts of the body were of the same character,
whether the embryo had developed in darkness or light.

Another prawn was kept in the dark thirty-eight days, and on exposure to the light it pre-
sented the same appearance. As in the other cases, as soon as light reached the eye the distal
retinule began to retreat to a deeper level. At first the black pigment which characterizes these
cells extends out to the cornea. After an exposure of two minutes to direct sunlight a slight
transparent band is seen below the cornea. This light zone increases as the pigment continues its

z retreat until, in the course of three-quarters of an hour, the distal retinule ensheath only the
lower ends of the cones.

In another experiment a prawn was left only about twenty-four hours in darkness. The same
effects were produced in the eye, which assumed its former condition after being in the diffused
light of the room twenty-five minutes. The distal retinular cells thus respond very promptly to
the action of the light, and in the course of a few hours (the exact time needed was not determined),
if excluded from the light, completely enshroud the proximal ends of the cone cells.

In the eye of Paleemonetes, taken in ordinary daylight, there are three distinctly marked strata

' of pigment between the basement membrane and the cornea, a proximal narrow stratum of yellow-
ish brown pigment belonging to the accessory pigment cells; a wider and much lighter area
peppered with dark granules, pertaining to the proximal retinular cells, the nuclei of which form
a conspicuous belt or layer on a level with the distal extremity of the rhabdoms. Lying close
upon the tier of retinular nuclei is a thin stratum of intensely black pigment, composed of the distal
retinular cells. As stated above, there are two of these cells to each ommatidium, and they each
send out a slender thread-like process, which extends in some cases as far forward as the corneal
cuticula, where it is possibly attached. I have not detected any similar prolongations in the direc-
tion of the basement membrane. Below the level of the cone, which terminates abruptly in a
convex proximal surface, the cone cells are prolonged into a long slender stalk consisting of proto-
plasm or of a refractive substance of a different nature from the cone. The cone cells are not
apparently prolonged below the level of the retinular nuclei. The distal retinuiar cells thus sur-
round the proximal ends of the cone cells.

In the eye exposed for thirty-eight days in the dark the distal retinular cells form a stratum
about midway between the corneal cuticula and the layer of nuclei of the proximal retinular cells.
The nuclei occupy a central position in this layer. Pigmented pseudopodia extend forward to the

s cornea, and occasionally a cell shows a slight inward prolongation. Had the cyes been preserved
without bringing them into the light, even for a moment, the distal retinular cells would undoubt-
edly have occupied a still more peripheral position.

In the eye kept in the darkness for the same length of time and afterwards exposed to the
light for five hours the distal retinular cells have retreated until they lie around the proximal

ends of the cones. The nuclei of these cells lie immediately upon the nuclei of the proximal retin-
ular cells, and it is interesting to notice the pigmented body of each cell folded on itself. In
section the pigment takes the form of plaited black ribbons. When the eye is again stimulated
by light the ribbon unfolds as the cell travels forward.

These cells are called by Exner the iris pigment, since they regulate the brightness of the
retinal image in much the same way as the vertebrate iris does.

X.—SUMMARY.

» In the review, including Sections v-1x of Part Second of this memoir, the principal embryo-
logical facts have been summarized, and it will now suffice to recapitulate only some of the more
¥ interesting results.

“—) ‘es 7... ee a.

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456 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

s

PAkT I,

Metamorphosis.—(1) The majority of the Alphei hatch as zoéa-like larve, while two species are
known, A. heterochelis and A. sauleyi, in which the metamorphosis is abbreviated. This shortening
of the metamorphosis appears to be directly related to the habits and environment of the species.
A. heterochelis has one metamorphosis at Beaufort, North Carolina, a more abbreviated develop-
ment at Key West, Florida, and, if we are right in considering the Bahaman form as a member of
this species, at Nassau, New Providence, the metamorphosis is complete or unabbreviated. The
Nassau form of Alpheus saulcyi either has the metamorphosis greatly abridged or ‘it hatehes with
all the external characters and the instincts of the adult. When we inquire into the modes

of life of these species we find the remarkable fact that the Nassau Alpheus sauleyi is a parasite or_

commensal, living in the pores of certain sponges, and the metamorphosis is completely absent or
profoundly modified. The Floridian Alpheus heterochelis is a parasite in sponges, and has its
metamorphosis greatly abridged. The Beaufort heterochelis, which must be regarded.as descended
from the Floridian stock, bas its metamorphosis less abridged than in the latter case and it is
uonparasitic. However, we still find it occasionally producing small eggs, indicating a tendency
to revert to the old metamorphosis, long since abandoned. Even if we decide that the Nassau
heterochelis has had a different genealogy from that of the Beaufort variety, we still have strong
evidence to show that the metamorphosis of the species may change in accordanee with a change
in habits and environment.

Variation and Habits.—(2) Alpheus heterochelis of Beaufort presents an interesting variation
in the structure of the small chela, which appears to be a sexual one.

(3) In many Macroura as well as Brachyoura, and especially in the Alpheus, one of the claws
is enormuusly enlarged, often nearly equal in size to the rest of the body of the animal. This great
chela may be either on the right or left side of the body, but it almost invariably follows that all
the young of a brood have the large claw on the same side, indicating that this characteristic is
inherited from the parents, and that where both of the latter bave the right or left claw enlarged
they give rise to right and left handed broods, respectively.

(4) Alpheus sauleyi presents very profound variations, and some of these varieties would
undoubtedly be regarded as distinct species by systematic zodlogists if the intermediate forms
were unknown. These forms are described and discussed in Sections v and yit of Part First.

Species living side by side show no tendency to commingle, and hence we conclude that the
striking varieties which we are here met with are not the result of hybridism, but are confined
to a single species. Two well-marked varieties occur, which I have distinguished as Alpheus
sauleyi, var. brevicarpus, and A. saulcyi, var. longicarpus. Between these forms every intermediate
stage is found.

The color variations in this species are also exceptionally marked. In all respects the males
appear to be more variable than the females. The structural peculiarities of the mother appear
to a large extent in the offspring, and if the swamping effects of intercrossing should be elimi-
nated it is likely that this species would soon become separated into at least two distinct forms.

It seems most probable that the change in habits or environment which this species has under
gone, has acted as a direct stimulus to variation.

PART Il.

Structure of the Larva of Alpheus saulcyi.—(5) The structure of the first larva of this Alpheus
reaches a very high degree of complexity, which is but little exceeded by that of the mature adult
form.

The green gland does not vet appear to have an external opening. The five pairs of gills

present at this time are also rudimentary, and the reproductive organs are only represented by a.

small cluster of large cells on either side of the middle line, between the digestive tract and the
anterior end of the heart. For the histological details, reference must be made to Section I of
Part Second.
The Ovary and Ovarian Egg.—(6) The ovary consists of an eeheenal: stroma of muscular and
couuective tissue and a lining epithelium. The ova arise from the lining epithelium, and each egg

. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 457
is differentiated from a distinct epithelial cell, the nucleus of the cell becoming the nucleus or
germinal vesicle of the egg. Some of the epithelial cells enwrap the developing ovum and form
the follicle or pocket in which it is lodged. The chorion or inner egg membrane is the direct

3 secretion product of the follicular cells.
(7) In Homarus and Palinurus the character of the germinal epithelium is somewhat different
from that of Alpheus. The outline of individual cells is obsenared and the germinal epithelium

; extends inward from the wall, in the form of radial sheets or folds, between which are reéntrant
; blood vessels. ‘There are a number of germogenal areas corresponding to the folds in which the
ova originate. During growth the eggs gradually pass from the center toward the periphery.
4 In the germogen the cell outlines are obscured.*
2 (8) The yolk arises within the cell protoplasm, and in Homarus degenerating nuclei occur in
the ovarian stroma, and it is probable that a certain number of nuclei degenerate and enter into
. the food yolk of the egg. In the lobster also some of the follicle cells develop into gland-like struc-
tures which characterize the mature ovary. They appear to have a direct relation to the growing
a eggs, but their true significance has not yet been ascertained. In about two weeks after the eggs
; have been extruded these structures have almost wholly disappeared.
j (9) L have observed a single polar body in a section of the egg of Stenopus, in which the male
and female pronuclei were present, and two polar bodies in the ripe unextruded egg of the lob-
ster. In lobster’s eggs also which failed of extrusion at the proper time, and which eventually
7 degenerate in the ovary, I find that the nucleus is at the surface. It has the appearance of a
: female pronucleus. It is thus probable that the polar bodies are often, if not always, given off
ae before the eggs are laid. t
. Negmentation in Alpheus minor.—(10) The segmentation in Alpheus minor is in some respects
anomalous, and the conclusion seems to be warranted that we have here a case of amitosis, unlike
: anything which has been hitherto described in Crustacea. Unfortunately my material is not at
eae present sufficient to enable me to say in exactly what way the usual process of cell division has
> here been wodified.
; Delamination.—(11) The segmentation has been thoroughly reviewed in Section vy, and
; it is unnecessary to repeat the details. I wish to call attention, however, to the fact that at
| the close of segmentation in the lobster some of the blastodermie cells delaminate and their
4 products pass into the yolk. In Alpheus sauleyi a similar migration of cells from the superficial to~
‘ the deeper parts of the egg occurs, but in this case it was not determined whether this migration
: was preceded by delamination or not. These cells appear to originate in greatest number over
that side of the egg which corresponds in position to the embryonic area. It seems possible that
a these cells may represent a primitive endoderm, the function of which has been usurped. In the
lobster they speedily degenerate.

Invagination Stage—(12) The invagination stage, which soon follows, results ia the admis-

sion of more cells into the yolk and in the formation of an organ called in this memoir the ventral

_ or thoracic-abdominal plate. Cells also_ continue to pass into the yolk from the ventral plate,
While cells are constantly being subtracted from the plate, it is constantly receiving new recruits
from the surface, owing to the activity of cell division in this region. .We thus have in Alpheus
a multitude of migrating cells, derived originally from three sources: from the blastoderm, from
the cells which are first invaginated, and from those which originate later from the ventral plate,
after all trace of the superficial pit has disappeared.

Germ-layers.—(13) These migrating cells, which are collectively called “the wandering cells”
in Section vil, spread to all parts of the egg. While it is perfectly obvious that these bodies
represent mesodermice and endodermice tissues, it is not so easy to determine what particuiar cells
give rise to this or that layer, nor iS it easy to décide in many cases, from a superficial study, whether
migrating cells may not be derived from the ectoderm in various parts of the embryo. This sub-

y

“The structure of the ovary of the lobster has been recently described by Bumpus in a detailed paper upon the

ae ae ee he.

embryology of this species. He has called attention to the folded character of the ovarian epithelium, which is so
# marked in the young or immature ovary. (The Embryology of the American Lobster, by Hermon Carey Bumpus,

Journ. of Morphology, Vol. v, No. 2, 1891.)
t Polar bodies have been recently described in the external eggs of the Jobster by Bumpus. Op. cit.

458 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

ject is fully considered in Section vu, the general results being: (1) That it is not possible to
decide what part the primary yolk cells play in Alpheus, for reasons which have been already
considered; (2) that the great bulk of the cells which migrate forward from the area of invagina-
tion and attach themselves to the embryo, or proceed to the peripheral parts of the egg and take
up a position at the surface, are undoubted mesoblastic elements; (3) that those celis which give
rise to the endodermal epithelium in the egg nauplius are derived largely from cells which migrate
in a posterior direction from the area of invagination ; (4) that degeneration, followed by the death
and dissolution of the chromatin and cell protoplasm, is characteristic of the wandering cells at
about the beginning of the egg-nauplius period. The mesoblast has become a well-recognized
layer before the endodermal epithelium has appeared.

(14) The egg, with centrally moving cells which have budded from the blastoderm, may be
compared with the planula stage of Coienterates, and the internal cells may represent the primi-
tive endoderm. According to this view, the invagination stage has no reference to an adult
gastrula-like ancestor, but is a purely secondary condition, which became so impressed upon the
ancestors of the present Decapods that it has remained in their ontogeny.

In the majority of Decapods which have been studied theinvagination has no direct relation
to the mouth or anus, or to the alimentary tract. The conditions which are present in the cray-
fish cannot be regarded as typical or primitive.

(15) In Alpheus and Homarus the primitive mouth arises on a line between the rudiments of
the first pair of antenn, but these appendages are never post-oral. The hind gut originates as a
nearly solid ingrowth, apparently at a point considerably behind the position of the pit due to the
first invagination, and is formed one or two days later than the mouth.

Cell dissolution—(16) The degeneration of embryonic cells is treated at length in Section v1.
It is remarkable that the early segmentation stages of Alpheus minor are attended with the degen-
eration of protoplasm. The chromatin residues remain for some time in the yolk, and eagerly
react upon dyes, but gradually lose this power and eventually enter into the general nutrition.

(17) Degenerating cells appear in greatest force in Alpheus, Astacus, and Homarus at about
the egg-nauplius stage, and from that time their numbers begin to wane. They appear in one
instance before the differentiation of the germinal layers, and are not confined to any one layer at
a later period, but in Alpheus saulcyi they are most characteristic of the wandering cells, which
represent mesoderm and endoderm. The “secondary mesoderm cells” and “ white-yolk elements”
which have been described by Reichenbach, are to be regarded as degenerating cells. Degenera-
ting cells also occur in connection with the ‘“ dorsal plate.”

The Eyes.—(18) The details of the structure and development of the eyes and nervous system
are fully reviewed in Sections VIl and Ix.

The eyes and optic glanglia are derived from the optic disk, in the formation of which there is
in Alpheus ho proper invagination. The thickening of the disk is accomplished by emigration
from the surface and by the delamination of superficial cells. An area of active cell division can be
distinguished, which corresponds to the invaginate area of the optic disk of the erayfish. The
cells which migrate from the center give rise to the rudiment of the optic ganglion. The disk
grows out in the form of a lobe, and becomes differentiated into an outer retinal layer and an inner
ganglionic layer. The eye proper is differentiated from the retinogen, which is primitively a single
layer of ectodermie cells.

(19) I am inelined to regard the “compound eye” not as an aggregate of simple eyes, as its
name implies, each of which is due to a hypodermal infolding, but rather as a collection of differ-
entiated clusters of ectoderm cells, originating in a single epithelial layer.

(20) The absence of light has no appreciable etfeect on the development of the eye pigment,
but in Palemonetes the distal retinular cells respond very promptly to the action of light. If the
light is excluded from the eye, these cells migrate outward and enshroud the proximal ends of the
cones, sending out pseudopodal prolongations to the cornea. When the eye is again stimulated by
light the pigment immediately retreats from the surface, and the cell takes the form of a plaited
black ribbon, leaving the cones free.

ADELBERL COLLEGE, F

«

s MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 459

XI.—REFERENOES.

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XUI-xXv. 1877.

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21-23, Figs. 1-8, v Jahrg. 1882. :

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of the Johns Hopkins University, pp. 1-76, Pls. i-vu1. Baltimore, January, 13891.

. Miuier, Fritz. Palewmon Potiuna. Kin Beispeil abgekiirzter Verwandlung. Zool. Anz., No, 52, pp. 152-167.

1850.
Berichtigung, die Verwandlung des Paleemon Potiuna betreffend. Zool. Anz., No. 55, p. 233. 1880.

. Nuspaum, JosepH. L’Embryologie @Oniscus murarinus. Zool. Anz., No. 228, pp. 455-458. 1886.

L’Embryologie de Mysis Charmeleo. Arch. de Zool. Expér. et Génerale, 2d Ser., T. 15, Nos. 1-2, pp. 123-202,
Pls. I-x11. 1887.

}. Packarp, A. S. Notes on the Early Larval Stages of the Fiddler Crab and of Alpheus. Amer. Naturalist, Vol.

XV, pp. 784-759, Figs. 1281.

. Parker, G. H. The Histology and Development of the Kye in the Lobster, Bull, Mus. Comp. Zool., Vol. xx, No.

1, pp. 1-62, 4 Pls. 1890. “ >
The Compound Eye in Crustaceans. Bull. Mus. Comp. Zool., Vol. xx1, No. 2, pp. 45-140, 10 Pls. 1891,

. Parren, WintiaM. The Development of Phryganids, with a Preliminary Note on the Development of Blatta

Germanica. (Quart. Journ. Micros. Sci., Vol. xxiv, New Ser., pp. 549-602, Pls. xxxvi A, B, C. 1884.

. ——. Eyes of Molluscs and Arthropods. Mittheil. Zool. Station zu Neapel, B. v1, H. ry, pp. 542-756, Taf. 28-32.

1886.
——. Studies on the Eyes of Arthropods. I. Development of the Eyes of Vespa, with Observations on the
Ocelli of some Insects. Journ. of Morphology, Vol. 1, pp. 193-227, 1 Pl. 1887.

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Leipzig, 1829.
Zur Entwickelungsgeschichte der Dekapoden. Archiv. f. Naturgesch., B. vi, pp. 241-249. 1340.

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phology, Vols u1, No, 2, pp. 291-386, Pls. xv-xxr. 1889.

APPENDIX I.
THE LIFE HISTORY OF STENOPUS.

_ Since this paper was written Chun has described (Die pelagische Thierwelt in grésseren Meere-
steefen, Bibliotheca Zoologica, 1, 1888) a small transparent crustacean which he calls Meiersia
clavigna. It occurs at the surface and also at various depths down to 600 M. A comparison of
his description and figure (Taf. tv, Fig. 6) with the Stenopus larva shown in Pls. 1x and x of this
memoir shows that Chun’s Meiersia clavigna is undoubtedly a Stenopus larva, a little older than
the one shown in Pl. x. (W. K. B.)

It is suggested at the bottom of page 340 that the cement by which the eggs are fastened to
the abdomen may possibly come trom the oviducts. According to recent observations of Cano
(Mittheil Zool. Stat. Neapol., 1X, 1891; abstract in Journ. Roy. Mic. Sov., No. 83, 1891) this is
derived from cement glands situated in Stenopus under the epidermis of the pleopods. It is
thought by Cano that these glands, to which the secondary egg membrane is due, are modified
glands of the appendages, and that the cement substance may serve as the medium through which
spermatozoa reach the ova, In order to reach the eggs the sperm cells probably pass through
pores in the chorion.

This paper was written in the summer of 1888, before I had seen the report of Spence Bate on
the Challenger Macrura (Report on the Crustacea Macrura dredged by H. M.S. Challenger during
the years 1873~76, Zoology, Vol. xxtv, p. 209, Pl. xxx, 1888). The Challenger brought home
only two specimens of Stenopus hispidus, one fiom erate: Fiji Islands, and one from Bermuda.
Spence Bate says that Stenopus has been ‘chiefly recorded from the eastern seas and the shores
of India by Desmarest, Milne-Edwards, and Sir Walter Eliott; from Japan by de Haan.” It has
been thought that Squilla greenlandica of Seba, which appears under several names, may be the
same as Stenopus hispidus. “The genus,” says Bate, “thus appears to inhabit regions so widety
apart as Greenland in the north, the Bermudas and Mediterranean in the west, and the southern
coasts of India and the Fiji Tslestae in the east. It has been found in the cold waters of the Arctic
regions as well as in the warm shallow waters of the tropics, but, despite this cosmopolitan range,
it has not been recorded as having existed in any geological formation.”

While the conelusion that the Arctic form is a Stenopus may be correct, it seems highly im-
probable that it is specifically related to Stenopus Atepuias. There is no evidence at least to show
~ that this is the case.

Bate figures a late egg embryo of Stenopus (Fig. 40, p. 212), and erroneously concludes that
the animal has a short metamorphosis and that it hatches as a “‘Megalopa.” He also gives a draw-
ing (PI. xxix, Fig. 2, v.) of the first larva of Spongiola venusta (a prawn which is placed by Bate in
the tamily Stenopide). This is clearly not a zoea, but a protozoea, as is better shown by the sketch
of the recently hatched larva (Fig. 42, p. 216) by von Willemoes Suhm, and the strong resem-
blance which it bears to ne protozoea of Bionbpus hispidus is very striking (compare with Pl. vu,
Fig. 11, of this paper).

462 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

According to Bate the branchial formula of Stenopus was first elucidated by Huxley in his
memoir on the classification of crayfishes (Proc. Zool. Soc., London, 1878). There are six pleuro-

branchie ; eleven arthrobranchiz, five of which are anterior and six posterior; one podobranchia,

and six mastigobranchie, of which the first is the only efficient appendage.
Spence Bate states that after careful comparisons he failed to find specific differences between
specimens from the Eastern and Western Hemispheres.

ERRATA.

As numerous errors have unavoidably occurred in this paper, I will correct the more important
of them.

Page 341, line 8, for *‘ Pl. vir” read Pl. x.

Page 341, line 13, for ‘* Lesneur” read Lesueur.

Page 343, line 2, for ‘‘ cells have spread more rapidly at a given point on the egg” read cells have increased more
rapidly over a given area of the egg.

Page 343, over table for ‘‘ Temperature 80° F.,” read Temperature of air, 80° F.

Page 344, lines 11, 16, 31, 32, and 47, for “ Fig. 10” read Fig. 11.

Page 344, line 18, for “‘ largely developed” read highly developed.

Page 345, line 20, for ‘‘ Fig. 10” read Fig. 11.

Page 345, line 30, for ‘‘ Fig. 11” read Fig. 10.

Page 345, line 38, for ‘‘ the first and second maxillipeds” read the amd and third maxillipeds.

Page 346, line 31, for ‘‘ larger than telson” read longer than telson.

Page 347, line 16, for ‘‘ x11 and Fig. 40” read x1 and Fig. 39.

Page 347, line 29, for ‘‘and 38” read and 39.

Page 347, lines 37 and 41, for ‘‘ Pl. x1” read Pl. x11.

Page 347, line 40, for “ Figs. 43, 45” read Figs. 43, 44.

Page 347, line 47, for ‘‘ Fig. 47” read Fig. 46.

Page 348, line 15, omit “‘errinem--_- -- larve.

Page 348, for lines 32-34 read: Body nearly cylindrical; tergal surface covered with spines. Carapace witli
prominent laterally compressed rostrum and distinct cervical and branchio-cardiae grooves. Outer antenne with
long bristle-bordered scale bent under the inner antenne toward the middle line, Second maxillipeds with setig-
erous lamina, attached to endopodite.

Page 348, line 46, for ‘‘ a marked transverse fossa” read a marked cervical groove.

Page 348, last line, for “‘ transverse furrow ” read cervical or mandibular groove.

Page 349, line 17, for ‘‘ Fig. 40” read Fig. 39.

Page 349, line 21, for “ their inner borders which meet in the middle line” read the inner honda of the exopo-
dites which meet in front.

Page 349, line 23, for “‘ Fig. 39” read Fig. 38.

Page 349, line 25, for “ Fig. 38” read Fig. 36.

Page 349, line 39, for ‘‘ Fig. 48” read Fig. 45.

Page 349, seventh line from bottom, for “‘the great chelw ” read bearing the great chele.

Page 390, first line, for ‘‘ Fig. 48” read Fig. 47.

Page 350, first and second lines, for “bearing a shorter proximal one below” read bearing a longer tooth and a
shorter proximal one below. ;

Page 350, line 9, for ‘* Fig. 41” read Fig. 40.
* Page 350, table, tenth line from bottom, for ‘‘ Length of chela” read Length of chela of same.

Paye 352, line 10, for ‘‘hartschilig” read hertschalig.

Page 352, tenth line from bottom, for ‘‘Crustaces, Arachnidses” read Crustacés, Arachnides,

APPENDIX I.
PARASITIC FUNGUS IN THE EGG EMBRYOS OF ALPHEUS SAULCYI.

The remarkable parasite of Alpheus sauicyi, to which allusion was made in Part First of the
Memoir on the development of Alpheus, is illustrated in Fig. 199, Pl. Lim. Although a large num-
ber of egg-bearing females were examined and their eggs were sectioned, only a single female (a
small specimen, probably var. longicarpus, obtained from the ‘loggerhead sponge” at Abaco) was

found to be infested with this singular parasite. We may therefore regard it as very rare under

these conditions. -

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 463

The sections of these embryos were very kindly examined by Professors Joseph Leidy and W.
G. Farlow. In reference to them Dr. Farlow writes as follows:

The parasite is certainly of great interest. I cannot find any description of it in botanical literature, although
it appears to be a fungus belonging to Chytridiacex.

The fungus has no mycelium, but is composed of single cells of various sizes. In a section
like that shown in Fig. 199 nearly one hundred large cells or cysts can be counted, and it is seen
that the peripheral parts of the embryo are packed with them. These embryos were alive,
although the embryonic cells were considerably altered from their normal condition, where they
came in contact with the parasitic growths and showed traces of degeneration.

The parasitic bodies are mainly (1) large naked cysts or encysted cells, and (2) very small
spore-like bodies. The naked cyst (¢. s., Fig. 199) is a thick shell which has collapsed and curled
up with the eseape of its contents. It is yellowish and is unaffected by staining reagents. The
surface of the cyst is covered with very uniform, short projections or tubercles, which refract the
light in a characteristic way.

Other eneysted cells contain a protoplasmic reticulum (es'), and there are very similar but
smaller bodies which are either naked or possess but a slight cuticular wall. These encysted
bodies just described possibly represent zoosporangia, and give risé to the myriads of minute
spores which occur in close relation with them. The spores (Fig. 199, sp., represented by small
black dots) are minute, oval, and highly refractive. In the eye and other organs certain nuclei
take up the stain very eagerly and refuse to part with it. These are probably the nuclei of em-
bryonie cells which have undergone modification. Occasionally one of the cysts appears black
(es?), which is due mostly, if not wholly, to refraction.

According to Goebel, reproduction in the Chytridiee is effected by means of swarm spores.
Resting cells occur, which germinate and become sporangia, producing large numbers of swarm
spores. Some forms, like Chytridium, have no mycelium. Its single cells, which live on or within
the host plant, after reaching their full size become zoosporangia. These give rise to swarm
spores, which are liberated into the water. The Chytridiee are described as parasites on other
aquatic plants, Fungi, Algze, and Phanerogams.

_ According to De Bary resting spores are known to occur in certain species. These develop
directly into sporangia or produce them after a short intermediate stage, and appear to resemble
the sporangia in size and in possessing a warty cellulose coat.

APPENDIX III.

Some early abstracts of this work (Alpheus: A Study in the Development of Crustacea) were
included in the Introduction published in the Johns Hopkins University Circulars, No. 97, April,
1892. The part relating to the embryology of Alpheus was here printed in its unrevised form,
and differs materially from the results of later studies which are given in this memoir.

While this work was in press it was thought best to change the name Alpheus minus of Say
to the correct form, Alpheus minor. As some of the pages were stereotyped before this correction
was made, both forms of the name appear.

ADELBERT COLLEGE,

Cleveland, Ohio, May, 1892,

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Plate I.

WK. Brooks, del,

Sachs & Withline Lethergracihing Co Mew York

ALPHEUS MINUS AND GONODACTYLUS CHIRAGRA.

/ oe A Fe d aS
MEMOIRS OF THE NATIONAL ACADE

i

Sy Poe Beeman Be |

z “ ‘ J a " ee
Alpheus heterochelis, drawn from life by Ww. K. Brooks. (Four times life-size.) _

a) se é

/

. Si,

Plate I.

WK. Brooks, ded. bas eknineooeseaaeion
ALPHEUS HETEROCHELIS.

MEMOIRS OF THE NATIONAL ACADEMY OF §

Pate TL = :

Gonodactylus chiragra, drawn by W. K. Brooks.

_ Adult female of the green variety, in her burrow, with eggs, twice natural size.

i. =

Memoirs National Academy of Sciences, 1889. PLATE III.

W. K. Brooks, del.

GONODACTYLUS CHIRAGRA.

Bit Eas,

470 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Prate IV.

Adult male and female of Alpheus saulcyi, var. brevicarpus, from Nassau, New Providence.

Fie. 1. Lateral view of female from green sponge. x33.

Fic. 2. Dorsal view of the same. x33. Parts only of the ovaries are visible in Fig. 2, while the _
eggs, which greatly distend the abdomen laterally, show plainly between the bases of
the swimmerets. In Fig. 1 the small chela is bent downward, the position in which
it is usually carried. In Fig, 2 the chelz are represented in the attitude of defense.
The dactyle of the left ‘‘ hand,” or large chela, is raised preparatory to striking.

Fie. 3. Smallmale. L=+12in. x7. Drawn under slight pressure, owing to which the antennal
spines and the antennular exopodites have assumed an unnatural position.

The pos-
terior margin of the carapace is more correctly represented in Fig. 1.

\

Plate IV.

Sahoo 8 Retr athocrapung > Nee Yore

, del.

FAH

ALPHEUS SAULCY!I, VAR. BREVICARPUS.

wa

See.

en

Lg ae

y

472

Dorsal view of the saat male Ricnomss hispidus. Nassau, N. P., June, 1887. L=13in. L. first

Excepting the brilliant pigment bands the body and appendages are nearly white,’and could be

Puate V.

antenna, exopodite—3{ in., endopodite—33 in. L. second antenna= =4U in, x13.

better represented against a black background. The arching flagelia of the antennz
are greatly foreshortened, and the spines and sete are of necessity we empha-—
sized in a pen and ink drawing.

“SNGIdSIH SNdONALS
“pop 2rrtapy FY]

nm) many 2 eytnstonar MATOYTNAS BEERS
“

ha 4a »

ier ae

Te Pid) say ler BA tite ae
iy a His

«

© 0), fy

. Si .
i Ane i, De 3 i :
PA iit awe oar en al Ba See oy ty ancien

arches CRS L: eles gika me dD
“4. 1 Shell A a ~~ -.

4

oy
ry.

. .

: eat ae
7 ren aed? Poy ery a Ps.

474

Fig.

Fie.
Fic.
Fie.

Fig.
Fic.

Fie.

Hm Oo bo

(6

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. -

Puate VI.

. Part of section of egg, showing the male pronucleus. The female pronucleus lies nearer

the center of the egg, is less regular in outline and has less perinuclear protoplasm.
A single polar body (not represented) is seen in this section. It lies close to the sur-
face of the egg, beneath the membranes, not far from the male pronucleus. It appears
as a small mass of chromatin, which stains quite as intensely as the nuclei. Egg
about 6 hours old. x 276.

. Section of egg with four nuclei, none of which are at the surface. 152.
. Part of same section, showing the nucleus and surrounding protoplasm and yolk. x 276.
. Lateral section, cutting yolk segment on a level with the disk-shaped nucleus. Compare

Fig.5 a. Hight-cell stage. Age about 12 hours. x276.
Section through egg in eight-cell stage. Compare Fig. 6. Age about 15 hours. x 152.

. Surface view of egg in the third segmentation or eight-cell stage. The egg membranes

have been removed. The nuclei lie at a deeper level than they appear in the draw-
ing. Compare Fig.5. x78.
Section of egg in the fourth segmentation stage. Sixteen cells. x 152.

Fic. 8. Fifth segmentation stage. Age, 19 hours. Cells not yet at surface. x 152.
Wic. 9. Invagination stage. A solid ingrowth of blastodermic cells has taken place at Ig, where

a slight pit is formed. The section cuts obliquely through the invaginate cells. x 152.
REFERENCE LETTERS.

a, perinuclear protoplasm.

Ch, chitinous egg envelopes (removed, except in Fig. 5).
Ep, ectoblastic cell. ‘

Ig, shallow pit of invagination.

y.¢., yolk spherule.

Plate VI.

Fig.6.

ies
PPM)
CPS ERD
Dect

NO co

FH. Herrick, del.

Sac 18 Wilbelon Lather Co Mew York

STENOPUS HISPIDUS.

r~ wa Pa

Ine

\e-<

S — Ss, 7 ¥
Pink
| .

- # Ake yt

+

a= wy ai

MEMOIRS OF THE NATIONAL” ACADEMY OF SCIENCES.

Piare VII. . | Pg nee

Fic. 10. Left second maxilla of larva at the point of hatching, before the first molt. x 276. Com- ;

pare with Figs. 25 ané 21.

Fie. 11. First swimming larva, after the first molt, seen from below. Pigment cells, brown. ©
L= 7, in. (measured from tip of rostrum to median notch of telson). Length of

rostrum =;65 in. x70. =

Fie. 12. Right first maxilla of first larva, seen from the outer side. Sete welder thai Compare : :

Figs. 19, 25. x 276. ;

Fie. 13. Telson of larva before first molt, seen from below. Compare Fig. 11. The setie are

invaginated and covered with a loose cuticle. x 276.

Fic. 14. Right first maxilliped of larva on the point of hatching, seen from the outer side. Sete

invaginated. Compare Figs. 22,25. 276. =

Fig. 15. Labrum and right mandible of larva, seen from above. 276 ; 7
Fig. 16. Right third maxilliped of larva on the Bane of hatching, seen erate the outer side. Com-—

pare Fig. 25. 276. :

REFERENCE LETTERS. ; H =

a, ontermost spine in telson of larva at the point of hatching. 3
d, equivalent of a in first locomotory larva.
Lb, labrum.

>.

= ee ee ee eee ee, ee ee

Sack eh Witdeis Lamers phiog Co New York

FH. He

STENOPUS HISPIDUS.

;

478 MEMOIRS OF THE NATIONAL ACADEMY OF SC!

x rate, Pah ee RUATE SV LED Wiser i
Fie. 17. Second larva after second molt. L=,%}; in. x70. fe 73 ee
Fic. 18. Left mandible, outer side, of second larva. x 276. ig ace
Fie. 19. First maxilla of second larva. x 276. ye ae eae
Fie. 20. Telson of second larva, seen from below. x70. ; bey
Fic. 21. Left second maxilla of second larva, seen from the outer side. x276. Seas
Fic, 22. Right first maxilliped of second larva, seen from the outer side. x 276.

_REFERENCE LETTERS. ee po

—

i 9 9, gastric gland. ness ; ae
. . . . the dotted line in Fig. 20 points to the outer spine, the equivalent of d, Fig. 11. mies

Plate Vill.

At a f

BANG }

PA NAY o My

= we = Le

4 aa
ee

Say
= ss va
\\
\y
/

EH Merrick det.

STENOPUS HISPIDUS.

ail
| a? ae

#

MEMOIRS OF THE NATIONAL ACADEMY OF

na, drawn from

—
-
4

| = "d :
ree ! Ie
“i
jt Pete
ie ‘. : '
1 al 5 i
Paty oe | j *
i
ie’ sp i
|
“ Foe)
y fai
‘ } SI
a |
\ t PS
f } j
\ ;
/
I
|
\
j
ots PD ~
} ‘ We Se cree

life by |

Advanced pelagic larva of Stenopus hi.

Se

i

/

pe . eae

Beaufort, North Carol

‘us, trom

“W. K. Brooks.

WK. Brooks, ded.

STENOPUS

Plate IX.

nig Ce New York

~ ‘

tue beh Say

y W.-K. Bre

drawn from life b

4

i

aS
a
a
8
8
q
|
A
;
A
IS
&
©
mM
:
ie)
a
al
a

Dorsal view of a larva like the one shown in Plate TX,

Plate X

W K. Brooks, del.

STENOPUS

: i ie CoS eee a Nit SOT 6 AURIS NOs aah eats Bart: 57

Ae eee
484 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.
®
Puate XI. ;
Fic. 25. Embryo nearly ready to hatch, released from the egg membranes. x70. Some food

yolk is still unabsorbed; swimming hairs very rudimentary ; compare Fig. 11.
Fic. a Right first antenna of alder larva. x70.
Fic. 27, Profile view of hinder end of abdomen of same larva. x28.
Fic. 28. Second maxilla of same larva. x 276.
Fic. 29. Mandible of same larva. x 276.
Fic. 30. First maxilla of same larva. x 276.
Fic. 31. Portion of third maxilliped of same larva. x 70.
Fig. 32. Terminal segment of Second pereiopod of same larva. x 70.
Fic. 33. First pereiopod of same larva. x70. ‘ :
Fie. 34. Portions of third, fourth, and rudimentary fifth pereiopods of same larva. x70.

REFERENCE LETTERS.

A, I, first antenna.

A. IT, second antenna.

Md., mandible.

Vapd. I, III, first and third maxillipeds.
R., rostrum.

Th., Th. 1, first maxilliped.

Th. 3-Th. 5, third to fifth maxillipeds,
1, first maxilliped.

Plate X/

Fig. 27

Ca,

ic =

= a

at

Fig52.

FH. Herrick, del.

Sackett & Wei Latgraphing Co: New Yors
STENOPUS HISPIDUS.

‘>
——
~~

:
é

ee

IOTEY

S
o
*.
—

5-4) ny

.

iim wits

<=
eo

4
-

dex tA

ie ae:
eh ae

“Sea. wed

Prare XII. a

Fic. 35. Older larva, taken in the tow-net outside of Nassau Harbor May 7, 1887. L=9™™. L. — ey
of eye-stalk=2™™. L. between eyes=4.7™. x15. The long flagella of the antenne 3
are conventionally represented to bring them into the plate. They trail above and .

behind the animal as it swims eee the water.
‘

Plate XI.

Figure 33.

FH. Herrick, del. cts Wiens Labgaghg Ca Bw Yah
STENOPUS HISPIDUS.

cas Sige liar

Grid

o.

AE ee 7

sik.

Ye

i
af
ore
s
>
fz
ra

af

4 iy

488

. First maxilla, outer side. Adult male. »15.
. Lateral view of carapace of adult male. x5.

. Left mandible, outer side. Adult male. Seale re <2
- Stalk and portion of flagella.of left first antenna, seen from above. Aduit male. x5. oes

. First right pleopod of male, outer side. x14. 5
. Left second antenna with flagellum cut off near its base. Adult male. Seen from

- Second maxilla of adult male. x 14. :

. Right first maxilliped from outer side. Adult male. x 14.

- Right second maxilliped, from outer side. Adult male. x 14.

- Right third maxilliped, from under side. Adult male. SOL aera ate
- Right first pereiopod, under side. Adult male. x5.

. Right fifth pereiopod, under side. Adult male. x5.

= : - Prats XIII.

above. x5..

=

Pate XTIl

FH. Herrick, del. acc W thai Latregrazing Ce New Yor
STENOPUS HISPIDUS.

‘.
5

GZ "ss

A
Digan oe. oN at
ee iat vs ie wea tS

490 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

XN

+2) PraTrn oc by: : x

Metamorphosis of Gonodactylus chiragra, drawn from life by W. i Brooks.

Fic. 1. Dorsal view of egg just befere hatching. ~ ~

Fic. 2. Front view of the same egg. 3 Bao
Fie. 3. Side view of the larva immediately after hatching.

Fie. 4. Side view of the same larva after the first molt. |

Fic. 5. Side view of the same larva after the second molt. z

Fic. 6. Dorsal view of the larva at the beginning of its pelagic life. 3

ee laa
J \

° —
\
~ a \
e ~
— < =
~
-
= *
2b {
Y
é .
~ Sie ay ,
—_ ¢ a — yee ;
‘ ¥ OY ce ae ot a or
- 2 by 7 Sea Z

Plate XIV.

WK. Sroaks, del.

GONODACTYLUS CHIRAGRA.

492 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. |

= 4

Di: PuatTe XV.
Metamorphosis of Gonodactylus chiragra, drawn from life by W. K. Brooks.

ce : Fic. 7. Dorsal view of the larva shown in PI. xIv, Fig. 3. -
Se _ Fic. 8. Ventral view of the same larva.
ere? Fic. 9. Dorsal view of the larva shown in Pl. xtv, Fig. 4. 4 ot

Fig. 10. Ventral view of the larva shown in | Pl. 7M Fig. 5.
Fic. 11. An older larva in dorsal view.

Fic. 12. Same in ventral view.

Fic. 13. Raptorial claw of a still older larva.

. ?

AV,

Plate

WK. Brooks, del.

GONODACTYLUS CHIRAGRA.

494

Fig.
FIG.

Fig.
Fic.

Fie.

Fig.

Fic.
Fie.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Puate XVI.

Metamorphosis of Alpheus, drawn by W. K. Brooks and F. H: Herrick.

. Third larval stage of Alpheus minor from below, drawn by W. K. Brooks.
. Second larval stage of Alpheus minor, about one-tenth of an inch long, drawn from below

by W. K. Brooks. -

. Telson of the Nassau fourm of Alpheus heterochelis during the second larval stage, drawn

at 10 a. m., April 17, 1887, by F. H. Herrick.

. Second antenna of Alpheus minor during the first larval stage, from the inside drawn by

W. K. Brooks, May 13, 1881, D. 2. (Zeiss lenses.)

. First and second maxille of the Nassau form of Alpheus heterochelis during the fourth

larval stage, drawn by W. K. Brooks from a sketch by F. H. Herrick. The larva at
this stage is shown in Pl. x11, Fig. 3. ‘

. First maxilla of Alpheus minor during the first larval stage, drawn at Beaufort, June 2,

1881, by W. K. Brooks, D. 2.

. Second maxilla of the same larva.
. Mandible of the same larva.

Mate XVI

Brooks, & Herrich,del

ALPHEUS

J
f
;

a . oa ~
2 Se ee

‘- Pi

oie Py as ae

Ry eee

DS rata xy ° nes ae ‘ ‘ = La! pierec vere:
mR. MOK Feral ate cnrn eK, ice YB b rie ap ASO ERY o
Dy tiie ah oh on ee oe ue gil ope ee ee |

x 7 "tty

Eb rea tage inl ad
Baa af Sw
Wie eee

oe Ser

496 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Pirate XVII. poe

Metamorphosis of Alpheus, drawn from nature by W. K. Brooks. 5

Fic. 1. Side view of Alpheus minor after the’second molt and in the third larval stage. Zeiss —
A. 2. This larva was about ninety-five one-thousandths of an inch long from the tip
of the rostrum to the tip of the telson.

Fic. 2. Dorsal view of Alpheus minor after the first molt and in the second larval stage. This
specimen was hatched at 9 p. m., May 30, 1881, and the drawing was made at 9 a.
m.on May 31. The specimen was eight one-hundredths of an inch long.

Fic. 3. Dorsal view of a young specimen of Alpheus heterochelis from Beaufort. The specimen —
was one-fifth of an inch long. It was reared from the egg in an aquarium in the
laboratory, and it was fifteen days old when the drawing was made. It is a little
older than those which are shown in Pl. xx, Figs. 2 and 3.

Plate XVII

WE. Brooks, det.

Sacer Widsetnas Labegrasting Co Mew York

ALPHEUS

=

ae ae. o

Lele Oe Pre
is > ae

Le > © eS
is

Pas

\

498 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES,

Prare XVIIE
Metamorphosis of Alpheus, drawn by W. K. Brooks from sketches by F. H. Herrick.

Fic. 1. Side view of first or second larval stage of Alpheus heterochelis from Nassau, drawn oa
the night of April 15, 1887. Zeiss A. camera. 4 <3 ;
Fic. 2. Ventral view of the third larval stage of Alpheus heterochelis from Nassau, drawn aun
18, 1887. at.
Fic. 3. Ventral view of fourth larval stage of Alpi heterochelis from Nassau, ‘drawn APS are
21, 1887. eee
Fic. 4. First ramen of the first larval stage of Alpheus minor.

Plate XVIII

Brooks, & Herrich,del .

ALPHEUS

4
\ - * 7

ip eer Phee shee teria’? SW bereits Free wits cd RATS Beret UR ey
~ ; “ . bi 7 rl % Mote *
rind ‘ he ; a

at fs eo

wnhte PA Fa! Barwa Myers Pr tey parstt af

— ; hi , aR iets CO Sie ta

ESAT ee Foran nls al 9h a4 “qtie i
: visielat 7 i ie

: ° ya J

WIR eee ees Thre eee:

vs oi . ae

BPP Paley a) 1 ken wf

- = . h ae ey oy
eh TET Agra Sint bee Rt et fijecchs © Ps

as ? oy

500 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES,

=

&

Prats XIX.

Metamorphosis of Alpheus heterochelis at Beaufort, North Carolina, drawn from nature by W. Ko
Breoks.

Fic. 1. Ventral view of the larva immediately after hatching. ; : :
Fic. 2. Side view of the same larva. ‘ <
Fic. 3. Dorsal view of the antennule of the same larva.

Fic. 4. Ventral view of the antenna of the same larva. ; = 3;
Fic. 5. Mandible of the same larva. ; es
Fic. 6. First maxilla of the same larva. : : :
Fie. 7. Second maxilla of the same larva.

Plate XIX.

~~

= =

FSO

SSS eS

Sask ot & Wildehes Lathograyneng Co Mew York

W.K. Brooks, ded.

ALPHEUS

ae a.

a

ee, eas

VRPT IS gE Mn ope Oa aN at ep eee ae fer) oY,
" 3} Lan y dat = he £ ba ra = atl “a 4 & Mein :
502 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. EO hehe i
{=
#
PLATE,
Metamorphosis of Alpheus heterochelis from Beaufort, North Carolina, drawn from nature by W. K.
Brooks.

-

Fie. 1. Embryo just before hatching.

Fig. 2. View of a larva which was captured in the tow net at Old Topsail Inlet, North Carolina,
June 25, 1883. It is about eighteen one-hundredths of an inch long, and is a little
younger than the one shown in Pl. xvu, Fig. 3, and a little older than that shown in
Fig. 3 of this plate.

Vic. 3. Ventral view of a larva little younger than Fig. 2

Fre. 4. Telson and swimming appendages of the larva shown in Fig. 3.

Fic. 5 First maxilla of the same larva.

Fic. 6. Second maxilla of the same larva.
Fig. 7. First maxilliped of the same larva.
Fie. 8. Second maxilliped of the same larva.
Fic. 9. Third maxilliped of the same larva.

:—

Plate XX.

WK. Brooks, ded.

ALPHEUS

u

awh a “elie. ahi At Rie tg PS

Ween pay ree a

= oh Pan
oa

ie
“ax eo Bele, a ak tA:

we ey $

ue

“

Ny Abe Beaty Wipes .

ie

per rer

Ciaita er At ) Tear reps rE
erie iabakasr 4 or Boots si Saha = ish gi ures ei

sn

cies Ses soh ‘i er Ronee ee

fi
ae, MN £4 ns O

est a ‘? ure

rh ee

504 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 6 eee

Puate XXI.

Fic. 1. First larva of Alpheus saulcyi, var. brevicarpus, from “loggerhead” sponge. Hatched at
4 p. m., June 10, 1887. A small amount of unabsorbed food yolk remains in the
stomach. x 26. 7

Fic. la. Line to indicate length of larva. L.=3.5™™.

Fie. 2. Second larva of same, from brood hatched on evening of June 8. Food yolk neraly
absorbed. About twenty-four hours old. x 26.

Fie. 2a. Line to show length of larva. L.=4™™.

Fic. 3. Head of young from same brood. Four days old. x52.

f1G. 4. Right first pereiopod of larva of A. saulcyi, var. brevicarpus, before the molt preparatory
to stage shown in Fig. 1. Seen from inner side. x52. Swimming hairs of exopodites
rudimentary. ;

Fic. 5. Egg embryo of A. sauleyi, var. longicarpus, nearly ready to hatch. The large chela of the
left first pereiopod is conspicuous below the antennee. x46.

Fic. 5a. To show natural size of the same. Slightly too large. Dimensions: ;45 78> inch.

Fie. 6. First and second maxilla of first larva (Fig. 1) before preparatory molt. The parts are
gloved with the embryonic skin, which is usually cast off at the time of hatching.
x 227.

Fic. 7. Left first pereiopod of same, seen from inner side. X52.

Fie. 8. Third larva of Alpheus saulcyi, var. brevicarpus. From same brood as second larva, Fig.
2. Not over twenty-eight hours old. Food yolk not wholly absorbed. x26.

Fic. 9. Telson and rudimentary uropods, seen from below. x 52.

Plate X.X/

FH. Herrick, del.

ALPHEUS SAULCYI

—_. = =". s

a. o> s ¢. Ot *
eit aia eee 1 '=bo5
bs: 506 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.
| P
Prats XXII.

Fic. 1. Left second pereiopod of first larva of A. saulcyi, var. brevicarpus, from inside. x 64.
; $ Fic. 2. Left third pereiopod of same, from inside. x 64, ;

Fig. 3. First maxilla of first larva of A~saulcyi from brown sponge. x 255.
Fic. 4. Left second abdominal appendage of first larva of Alpheus sauleyi, var. brevicarpus. x 64.

24.
Fie. 5. Left first abdominal appendage of the same. x64. =
Fie. 6. Rostrum of the same, seen from above. x 64.
Fic. 7. Right second antenna of the same, seen from below. x 64.
: Fig. 8. Right first antenna of the same, seen from above. x64. ~ Z
Fic. 9. Second antenna of young of Alpheus saulcyi, var. brevicarpus, six and a half days old. x 64.
Fic. 10. First antenna of the same. x 64. $ i
’ Fic. 11, Head of male of Alpheus saulcyi, var. longicarpus, trom “ loggerhead” sponge. Median
Ba spine of rostrum wanting. Drawn from life. L.=5.5™™, 31.
Fie. 12. Mandible of first larva of A. saulcyi, var. brevicarpus. x 255.
Fig. 13. Left second antenna of male of A. sauleyi, seen trom below. No.8 of Table I, p. 385. x33.
Fic, 14. Left second antenna of female of A. saulcyi. From No. 9 of Table I. Xd: ;
Fie: 15. Small chela of larva of A. sauleyi, var. brevicarpus, shown in Vig. 17, at time of hatching.
Compare this with the same appendage of the adult. x64. _ te
‘Fig. 16. First pereiopod (small chela) of young of A. sauleyi, var. brevicarpus. From green sponge.
; Compare this with Fig. 3, Pl. xxiv. x 64. ; :
Fic. 17. Front of a larva of A. sauleyi, yar. longicarpus, which was hatched April 25. Drawn
) under pressure; eyes slightly distorted. Equivalent to the ordinary third larva, Fig.
Te 8, Pl. xxr x64.
Fig. 18. Part of stalk of right first antenna of male of Alpheus saulcyi, seen from below, showing
the auralscale. The median eye is seen on the right, between the basal segments of
the antennules. From No.8 of TablelI. x26.

)

Plate XXII

Sacken Widanions Laegraciuny Co New Yow

FH Herrick, del.

ALPHEUS SAULCYI,

Ae ‘ .

a ie ve. he} ye vite Tile
janet aS ae

Pir ASG aS
ies ff f ml
ee See LTE |

- Ae <> ¥ Aires 7 3 ; TC
oat a ain OD ; Litiieits Sighs The

508

. Right second pereiopod of male of Alpheus saulcyi, var. brevicarpus, seen from the outer |

. Terminal segments of right fifth pereiopod of the same. x33.

. Left mandible of the same, seen from the outer side. x 64. -
. Left first antenna, and left compound eye of the same, seen from above. x33.
. Left third maxilliped of the same, seen from outer side. x33.
. Right second maxilliped of the same, seen from the outer side. x 64.

. Right first maxilliped, seen from the outer side. x64.

. Right second antenna of the same, seen from above. x33.

oe

Puate XXIII.

side. x33.

| a oe

FH. Herrick ,del .

ALPHEUS SAULCYI.

Plate XXt/1

Fig 2.

r
‘

ie ma oat a Nh \— 3 “
es Se #ig Pa a
| i ERNE T Se :
510 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.
Prare XXIV. { :

Fic. 1. Right fifth pereiopod of male of Alpheus saulcyi, var. brevicarpus, seen from outer side.

x33,
= Fie. 2. Small chela of male of A. sauleyi, var. longicarpus. From No.9, Table I. x33.
aA _ Fic. 3. Small chela of male of A. sauleyi, var. brevicarpus. From No. 8, Table I. Compare with |
: the typical form of the other variety, shown in Fig. 2. x33.
Fie. 4. First pleopod of male of A. sauleyi, from “loggerhead” sponge. x33. ae
Bat, Fic. 5. Left first pleopod of femate of A. sauleyi, from “loggerhead” sponge. A single egg is seen,
we attached to three hairs of the protopodite. The hairs are coated with glue, and the
| gluey threads are twisted into a chord, which is continuous with a thin sheet of this
i substance (the membrane of attachment or secondary egg-membrane which envelopes
5 > the egg). Below is seen a single hair, from which an egg has broken loose. Drawn
s from an alcoholic specimen. x33.

Fic. 6. Right second pleopod of larger female of A. saulcyi, showing a number of eggs attached,
seen from behind. x14.
Fic. 7. First maxilla of A. sauleyi. Endopodite bent out of position, to a point below the large
a coxopodite. x64. é
; Fie. 8. Large chela of female of A. saulcyi, from “loggerhead” sponge. Compare with the Brea. = is
carpus shown in Pl. tv. x33. ie:
Fic. 9. Right second maxilla of A. sauleyi, seen from outer side. x64.

(Sait Pit a a ost i Pree Ws ae
fee a ah ae ee a eee terete) we

SO a

Plate XXIV.

PO eee eee yee eee

Sackeo & Wilbelms Lithographony Co New Yarie
ALPHEUS SAULCYI,

FH. Herrick, del.
*

.

phe Nee
Pi ely

,

= F<» a bars = a
Vaal hog EA eon

‘ “a
>
Ne

~~

La

Fatt t
dA et
ee

ase

512

Fic.
FIG.
Fic.
Fic.
Fic.

Fie.

Fie.

6.

The

eee z an, so ee tae! — + i tO ee ah. Sl al na “ om .
= . he Sd rng at « nied : Sey ska pa Sie gre F>
r Sit SEs ee EN Te re me

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

PuatTeE XXYV.

. Surface view of segmenting egg of Hippa talpoides. Thirty-two yolk pyramids present.

x 38.

. Embryo of Hippa talpoides, showing optic disks and thoracic-abdominal plate. x 38.
. The central part of a transverse section of the ovary of the lobster, Homarus americanus,

to show the progressive development of ova; from the same series as that repre-
sented, with less enlargement, in Fig. 6. Ovary taken in January. x 281.

. Section of egg of Hippa talpoides in yolk segmentation. Sixty-four yolk pyramids pres-

ent. x70.

. Part of segmenting egg of Alpheus minor, showing a single large nucleus and two smaller

nuclei. Compare with Fig. 23. x 281. :

Central portion of transverse section of ovary of the lobster, corresponding nearly to that
shown in Fig. 3, showing the germogenal areas and the irregularly radiating blood
sinuses. The diameter of the entire ovary is about twice that of the part represented.
The largest peripheral ova have an average diameter of about one thirty-third of an
inch, and their contents is only about one-eighth that of the ripe egg. _ x 70.

Egg-nauplius embryo of Hippa talpoides. Appendages appear as simple buds. x38.

Fic. 8. Post-nauplius stage of Hippu. Abdomen bilobed at tip. Buds of at least three pairs of

post-mandibular appendages. Figs. 1, 2,7, and 8 are made from pen-and-ink sketches,
and show only the general appearance of the embryo and its relation to the yolk.

REFERENCE LETTERS.

Ab. P., thoracic abdominal plate. =
B. C., blood cell.

Bl. S., blood sinus.

Ch., chitinous eggshell.

Ch. W., limiting membrane of blood sinus.

Ct. S., ovarian stroma.

EL. f., egg follicle.

F. C., egg follicle.

Ger., germogenal area.

I, E., ovarian stroma (undifferentiated).

0, o'-o7, nuclei of ovarian stroma and developing eggs.
O. D., optic disk. :

O. L., optic lobe.

Y. P., yolk pyramid.

Y. S., yolk spherule.

Vae., yolk vacuole.

Plate XXV.

HIPPA,HOMARUS AND ALPHEUS.

=

514 MEMOIRS OF THS NATIONAL ACADEMY OF SCIENCES.
!
PLate. XXVI_ .

Fie. 9. Section through segmenting egg of Alpheus sauleyi. Hight cells present. Yolk unseg-
mented. Egg membranes diagramatically represented. x 70. :

Fic. 10. Surface view of the same. Sixteen cells present. Yolk pyramids formed. The peripb-
eral nuclei are seen through a thin layer of yolk. x 70.

Fic. 11. Transverse section through the immature ovaries of Alpheus. Ovary taken in June,
from female “in berry.” Diameter of largest ovarian egg, one one hundred and
sixty-eighth of an inch. Diameter of extruded egg, one fiftieth of an inch. Contents
of ovarian egg, one thirty-seventh of that of the extruded egg. x 281.

Fig. 12. Section through segmenting egg of Alpheus minor, from Beautort, North Carolina, show-

: ing nests of nuclei. x70. :

Fic. 13. Swarm or nest of nuclei, like those of preceding figure. x 251.

Fic. 14. Section through egg of Alpheus minor, cutting segmentation nucleus. Nucleus elongated,
with irregular, indefinite boundary. x 70.

REFERENCE LETTERS.

Al. C., alimentary canal.

B. C., blood cell.

B. 8., blood space (possibly unnaturally distended).

Ch., chitinous egg envelopes.

D. A., dorsal aorta.

e, el, young ova.

F. E., ovarian stroma.

F. £.', follicular epithelium.

F.C., follicular epithelium.

Ger., germogen.

Ger.', position of germogen in ovary, with ova nearly ripe.
G. V., germinal vesicle.

O. W., ovarian wall.
SS, swarm of nuclear bodies.

Vac., yolk vacuole.

Vit., vitellogen.

x, cell shown in Fig. 30.

Y. P., yolk pyramid.

~
.
2
s

Plate XXVT.

F-H. Herrick, del. ine 8 Wiens sageghng re York
ALPHEUS SAULCYI AND A.MINUS.

Page ae
ard & >

— = Oe aS
7 inc} yee
as VE ¥ ".

tana"
tom. PA
Jae ee

se thie

Te ertads vivo dy a] 4

[igitergh &ovi

516 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ~

7

Puate XXVIII.

Fic, 15. Section of egg of Bahaman variety of Alpheus heterochelis in typical yolk pyramid stage
Sixty-four cells present. x70.

Fic. 16. Segmentation nucleus of egg of A. sauleyi, nearly central in position. x 277.

Fic. 17. Section of an egg of A: sauleyi, which was normally laid but unfertilized, showing the 5
female pronucleus. x70. ’

Fie. 18. Degenerating nuclei containing spore-like bodies, from the egg-nauplius embryo, the
structure of which is shown in Pls. XLI-XLIlI. Xx610.

Fic. 19. Blood cells of adult Alpheus. x 610. ;

Fic. 20. Endodermal cells from the ventral wall of the primitive alimentary cavity of Astacus
fluviatilis. After Reichenbach (54) Taf. vin, Fig. 67. This is taken from the egg-
nauplius stage to show the origin of ‘‘secondary mesoderm.” The elements here
marked m', k are described as cells which have originated from the endoderm, and
completed their metamorphosis into ordinary mesoderm cells. These may be com-
pared directly with J, Fic. 18, and s, s’, Fig. 21, from the egg-nauplius of Alpheus
sauleyi, and are rather to be regarded as nuclear bodies in the earlier stages of
retrogressive metamorphosis. x 256.

Fic, 21. Part of transverse section through the foregut of the egg-nauplius of Alpheus saulcyi, to
show the degenerative cell products. x 610.

REFERENCE LET'lERS.

A. Y.S., altered food-yolk.

Ch., chitinous egg membranes.

ec., ectoblast.

i., nuclear body, with vesicular chromatin mass.
k, k,l, m, m'-, nuclear products in yolk.

Mes., mesoblast.

N., N.', nuclei of entoblastic cells,

n., nucleolus of entoblastic cell (not clearly shown).
OL., oil drop.

Ret., protoplasmic reticulum.

S, 8, 8?., degenerative products.

Sep., cleavage plane.

Std., foregut.

Vac., yolk vacuole.

Y., yolk.

Y. P., yolk pyramid.

Y.S., yolk sphere.

Plate XXVII.

F-H. Herrick, del.

Sach a8 Wilhelm Lthegpraphu Co. New York

ALPHEUS AND ASTACUS.

Res Wn ee getting ree a ne Pe Pe tS ee ee ee ez etn uate Sah Nae ,
. ~ 2 ~ ane ey " meray J e : %
Ee Des : ;
- = B
- a re
518 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.
Pirate XXVIII ‘ :

Fia. 22. Part of section of segmenting egg of Alpheus minor from Beaufort, North Carolina, show-
ing nuclear body in clear area. x 277.

Fic. 23. Swollen, probably degenerating, elements, from segmenting egg of A. minor. X27.

Fie. 24. Section through base of yolk pyramid of egg of Palemonetes vulgaris. About sixty-four
cells present. x 277.

Fies. 25, 26. Two: successive sections through clear area in segmenting egg of Alpheus minor,
showing degenerative products and nuclear bodies in process of breaking up. x 277.

Fic. 27. Part of section through segmenting egg of Pontonia domestica, betore cleavage of the
yolk. The egg contains three nuclei, one of which is seen to be in karyokinesis.
x 277.

Fic. 28. Part of section of an Alpheus egg in same stage as that shown in Fig. 9. Cell dividing
indirectly and in horizontal plane. x 277.

Fria. 29. Section of-egg of Alpheus minor, probably at close of segmentation. x 277.

Fic. 30. Enlarged view of cell x, and part of section shown in Fig. 9. x 277.

REFERENCE LETTERS.

Ch., egg membranes.

N., nucleus.

P. A., protoplasmic area.

P.N., perinuclear protoplasm.

SO, SC, degenerating cell products.
Y, yolk.

Y. B., yolk ball.

Y.8., yolk sphere.

Vac., vacuole.

ALPHEUS AND PONTONIA.

Plate XXVIII

A Wittens Laeogragrony Co. Mew York

eS 2

e-

~~

x ,

Lae ie > od

ge abst
. :

att

&

520

Fie. 31,

Fig. 32.

Fic. 33

Fig. 34,

Fie. 35.

Fie. 36.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Puate XXIX.

Part of section of egg of Bahaman variety of Alpheus -heterdchelis, showing two yolk
pyramids. Same stage as Fig. 15. Sixty-four cells present. 277.

Part of transverse section of egg-nauplius of A. saulcyi, showing the fold of one of the
antenne and the mesoblastic cells and degenerative products contained within it.
x 610. ; -

Wandering cells in yolk above the same embryo, showing protoplasmic union. x 610.

Part of section of egg of the Bahaman heterochelis in egg-nauplius stage, showing wander-
ing cells, which have left the yolk and have attached themselves to the superficial
ectoblast. The nuclei are flattened against the surface, but are clearly distinguished
from the epiblast. x 610. :

Part of transverse section of older embryo, showing blood cells and wandering mesoblast
cell (Mes.). Eye-pigment beginning to form. x610.

Part of longitudinal section of embryo shown in Fig. 153, to show the degenerative prod-
ucts of the dorsal plate. x610.

REFERENCE LETTERS.

App., appendage. ay

A. Y.S8., altered yolk.

B. C., blood corpuscle. ~

Ch., egg membranes.

C. P., united pseudopodia of two wandering cells.
Ect., ectoblast.

Ep., spindle-shaped nuclei of surface epiblast.
Mes., Mes,', mesoblast.

Mu., muscle cells.

Pn., cell protoplasm.

Pl., coagulated blood.

s, s!, degenerative cell products.

Sep., inner wall of yolk pyramid.

S. W., outer wall of yolk pyramid.

Y. C., wandering cells.

Y.S., yolk sphere.

Vac., vacuole.

7

_»
,

XXIX

Plate

Sep.

rps

a aeue:
@

App.

FH. Herrick, del.

ALPHEUS

7

_?), 22081 Soe 2.

Baas

-
© eo ok

* aig
,

Me Oe ee, RN ae Sa ees git oo ae a
me Saal ae Pan eee gee wert f
r Oe hos ae i
Z ; ax a 3 a
522 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. — .
+
PATE OKO

Fic. 37. Part of section of egg before invagination stage, showing primary yolk cells. All the —
figures on this plate, excepting Fig. 46, refer to the Bahaman form of Alpheus hetero-
chelis. X27.

Fic. 38-44, Consecutive sections of the same egg, showing the progress of the primary yolk cells
in their migration from the blastoderm to the central parts of the egg. x70.

Fig. 45. Section through the same egg, showing semidiagrammatically the structure of the yolk.
x 70. ;

Fic. 46. Section through the egg of A. sauleyi at a slightly later stage, but before invagination.
The blastodermie cells lie at the surface, the primary yolk cells toward the center of
the egg. Traces of the primary yolk cleavage are still seen at the Rye and a
secondary cleavage has occurred below the surface. x 70.

Fie. 47. Surface view of the side of egg, corresponding ve the germinal area in nearly the same
stage. x70.

Fie, 48. Tangential section, showing tilastodarmic cells of same egg. x 277 5

REFERENCE LETTERS.

a, a7, cells migrating from blastoderm into the yolk,
Bd. C., blastodermie cell.

Ch., eggshell.

G. D., embryonic area.

Sep., yolk cleavage plane.

Y. B., yolk ball.

Plate XXX.

Fig.46. Fig. 47.

FH. Herrick del.

ALPHEUS

”

.

524 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

PuaTeE XXXII.

Fies. 49-55. Serial transverse sections through the embryo in the invagination stage.: In the
most anterior section the germinal area (G. D.) is traversed, and in Fig. 53 the shal-
low depression in the middle of the invaginate area is cut through. In Fig. 54 (G@.
D.) we see the forward extension of the invaginate cells and the first trace of the
thoracic-abdominal plate. The distinction between the primary yolk cells (Figs. 49,
52, 53-55) and the invaginate wandering cells (b, b?°, Figs. 52-54) and their product,
which now begin their migrations, is very plainly shown. In Fig. 50, which cuts
the shallow pit at the surface of the invaginate area, we see the amceboid cells with
large granular nuclei making their way from the bottom of the pit into the depths
of the yolk. Figs. 49, 52-55, x115. Figs. 50, 51, x 291.

REFERENCE LETTERS.

b, b?-b*, in-wandering cells derived from the invaginate cells and their products.
Ch., egg capsule or shell.
Ep., ectoblast.

G. D., embryonic area. y

I. C., invaginate cell.

Ig., pit formed by the invagination. 4
Y. B., yolk ball. E >
P. Y. C., primary yolk cell. : :
Y. S., yolk sphere. :

FH. Herrick, del.

i

Ep:-

ALPHEUS

——

a ee

Plate XXX1.

a co oe

-_—
©

¥ le &e 5S 5 f,)
526 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ~_

PrArE XOX:

Fics. 56, 59, 60. Longitudinal serial sections through the entire embryo in the stage shown in Fig.
58. Fig. 59 is median. The primary yolk cells (P. Y. C., Fig. 60) can still be distin-
guished from the wandering cells derived from the invagination (S. Y. C., Fig. 60).
In Fig. 59 a primary yolk cell (P. Y. €.') is in the metakinetic stage of division.
Traces of the primary segmentation of the yolk are still present, and the secondary
yolk segmentation is very marked in the neighborhood of the-wandering cells. —
> Where the shell (Ch.) is not removed it is seen to be considerably distended and to
have epiblastic cells sticking to #t, showing the close adherence which normally exists

between the egg membranes and the egg. x115. =
Fie. 57. Section through egg, cutting germinal disk just before invagination. Twenty and one-

half hours older than yolk-pyramid stage seen in Fig. 15. x75. ,

. Fic. 58. Surface view of embryo after the appearance of the thoracic-abdominal plate and the optie
\ disks. The shallow depression which marked the invaginate area has disappeared.
eae,» Its approximate position is indicated by Ig. Compare Jg., Fig. 59. x 291. ;

REFERENCE LETTERS.

; Ab, P., ventral plate.

3 Ch., eggshell.

Ep., Ep.', ectoderm.

G. D., germinal disk.

Tg., pit of invagination.

L. Cd., lateral ventral bands.

O. D., optic disk.

sige P. M., wandering cells, seen below surface, coming off from ventral plate.

= F ° P. Y. C., P. ¥. C2, primary yolk cells.

Sep., yolk cleavage plane.

S. Y. C., 8. Y. €.!, wandering cells derived from the invaginate cells and their products.

T. Cd., cell area unitiug optie disks. . :
Y. B., yolk ball. : a
Y. C., primary yolk cell.

sx

4

Plate XXXII

F’H. Herrick, det

ALPHEUS

{
4

_ ‘ y '

i ie > es en ae J eee! ee ee Pe See ia Cee | et eee eee Sie 4 i. al

Mee ty =o
°

UA

# Shiny ‘Yist s o Sea ’
- re bt Sead
528 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. __

Puate XXXITI.

Fics. 61, 62, 68, 69. Transverse sections of embryo in stage shown in Fig. 58, Pl. xxxu. Fig. 61

cuts the thoracic-abdominal plate, and Figs. 68 and 69 involve the optic disks. Pri-

zu mary yolk cells (P. Y. C.. Fig. 69) are still plainly distinguishable. 115.
Fic. 63. Portion of median longitudinal section of the same stage. The larger and clearer nuclei
3 in the invaginate area represent the mother cells of both mesoderm and endoderm.
% The yolk ball or secondary yolk segment is characteristic of this stage. 291.
Fics. 64-67. Consecutive transverse sections of left optic disk of same stage before any thicken-
ing has occurred. The most anterior section is represented in Fig. 64. 291.

REFERENCE LETERS.

Ab. P., ventral plate.
Ch., eggshell.
Ep., ectoderm.
% Ig., invaginate cavity.
ae : L. Cd., lateral ventral cord.
ay: O. D., optic disk.
een P. Y. C., primary yolk cells.
Sep., yolk cleavage plane.
S. Y. 4, in-wandering cells derived from ventral plate.
eS ¥. B., yolk ball. ; ;

Plate XXX1II.

FH. Herrick, det. “Secket 8 Wiens Labepraphiog Co New Yok
ALPHEUS

=
i

aig BNL

Swish
W

;
=

Rp

biti ie

s

Hes

jee

f Ad bee Pe

wi ,
:

a

#
#

io
oe

530 MEMOIRF OF THE NATIONAL ACADEMY OF SCIENCES.

eT.

PLatE XXXIV.
= MST (Stage IV.)

Fias. 70, 71, 73, 74. Longitudinal serial sections of the entire embryo in the stage shown in Fig.
72. In Fig. 73 the plane of section is nearly median. The primary yolk cells-are
now generally indistinguishable from the other wandering cells. Compare cut, Fig.
11, which shows the distribution of the wandering cells at this stage. 115. 7

Fic. 72. Surface view of embryoin Stage rv. Rudiments of the mandibles and first pair of antenne
are present. An area of cell ingrowth in the optie disks (C. M.) is characterized by
the large size of the nuclei. From them and their products the optic ganglion takes
its origin. Some of the surface cells on either side of the middle line were acciden-
tally cut away. x291. — -

REFERENCE LETTERS.

og A. (J.), proliferating center of first antenna.
Ab, P., ventral plate. /
C. M., proliferating area of optic disk.
_Ep., ectoderm. ase 2
L. @d., lateral ventral cord. =
Ma., proliferating center of mandible.
0. D., optie disk.
T. Cd., transverse cord uniting optic disks.
Y. B., yolk ball.
Y. C.,-Y. C.', wandering cells. : . -

Plate XXXIV.

Fig. 14.

fi
‘
fe
bine
iyi
‘

i “dy

Beer.

NX

FH Herrick, del.

ALPHEUS.

ae

an / ‘

v ha

ES 5 Ms a F

‘ ° en Ti TES
‘ é

nt

boZ MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. |

: |

Zs Puate XXXYV.

(Stage IV.) er

¥ p Fic. 75. Median longitudinal section of the entire embryo. One of the wandering cells, whieh is se
approaching the surface of the egg opposite the thoracic abdominal plate, is in the ey
process of division. 115.

Fias. 76-83. Consecutive serial transverse sections through the left optic disk of same, to illus- oa
trate the earliest stages in the thickening of the disks. The most posterior section a
iy (Fig. 83) cuts the first pair of antenne. x 291. Steet
is Fic. 84. Transverse section through the middle of optic disks. x 115. eee
el Fig, 85. Transverse section through thoracic abdominal plate, showing the multiplication of sur- be 4 ‘
a face cells, by which the plate is increased, and cells below the surface (Y. C.) which — ae. ie
P pass into the yolk. x 291. ry
td, : 7 ae
om " REFERENCE LETTERS. er
= ; A. (1), first antenna. - f We
Beets Ab. P., ventral plate. F tre Rae
“ie < “ Ch., eggshell. :
sm C. M., proliferating area of optic disk. 2
Ss. ec., ec. 8, ectodermic cells of ventral plate (Fig. 85). ec., (Fig. 80) ectodermic cell of optic disk.
Se ; : Ep., ectoderm. : + ee: -
y x 0. D., O. D\., optic disks. : ; és =
~ Ret , protoplasmic reticulum. ;

T. Cd., transverse cord. . =
Y. B., yolk ball. fe 5
Y. C., ¥. C.-, wandering cells.
Y. S., yolk sphere.

etre ty pre & 5 iid

as
=

te Bote
7 = "y
4 ».

ae

Hlate XXXV.

YC

eee

(0D: Fig.84)

ec.

wh

J

Fol

FH. Herrick, del. schol ie
ALPHEUS

ee eae.

ite

Aiiriee” GA"
eee - jm
crate Sry,

ee pet eS ee
ferns f Sr eis
, Bee anes Cee ey
534. MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. |

Puatr XXXVI.

(Stage VY.)

Fis. 86, 87. Parts of longitudinal sections of embryo seven or eight hours older than that shown
in Fig. 72. The optie disk (0. D.) is cut in Fig. 86, and in Fig. 87 its inner part is
involved, with the outer border of the thoracic abdominal plate. There is no sharp
demarcation between the protoplasm and the yolk, as is indicated by the dotted lines —
under the embryonic layers: x 291.

Fires. 88-89. Longitudinal serial sections through the entire embryo, somewhat younger than the
last, and six hours older than that represented in Fig. 72. The optic disk is sectioned

ae in Fig. 90 through its central proliferating area (C. M.), and the rudiments of ae

three naupliar appendages appear in Fig. 89. x 115.

Fic. 91, Transverse section cutting optic disks of embryo about nineteen hours older than that, of

; _ Fig. 72 and twelve hours older than that represented by Tigs. 86, 87. Wandering

Fy cells ( Y. C.') have traveled to remote parts of the surface, and earyokineae figures

Se (Y. C2, Fig. 89) prove that they are in active division, 115.

REFERENCE LETTERS.

A. (1), rudiment of first antenna.

A, (IT), rudiment of second antenna.
Ab. P., ventral plate. *

App., area of appendages.

Ch., eggshell.

C. M., proliferating area of optic disk.
ec., Migrating ectoblast cell.

Ep., ectoderm.

Md., rudiment of mandible.

O. D., optic disk.

S., product of degenerating chromatin.
St. 4., sternal area. es

T. Cd., transverse cord.

Y. C., Y. C.!-, wandering cells.

Y. S., yolk sphere.

Plate XXXVI

FH. Herrick, del. acon W dsinn LAbegrebing Ca Be
ALPHEUS

ar ay nS oe
g Be eth a eR: Scale at Es Ee
ig 2 j a4. oF - ph Ss 3 . Aran Md *
is yg ws . 5 : 4%
" 536 ‘ MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

.

+

2 Pirate XXXVI.
(Stages V-VI.)

ae Fie. 92. Part of transverse section, showing the structure of the keel-shaped ventral plate, and
: indicating the origin of mesoblast from the surface of the latter. x.291.
Fie. 93. Surface view of embryo with buds of naupliar appendages. The sateen area (St. A.)
is covered by a single layer of ectoderm. The invagination of the mouth has not
2 se yet appeared. Some nuclei of cells which lie immediately below the surface, especially
hee in the thoracic abdominal plate region, are represented. x 291. ; ‘ hae,
ag Fias. 94-95. Transverse sections of embryo, belonging to the same series as Fig. 92, to illustrate
; the structure of the thickening optic disks. Degenerating nuclear products (s.', s.2,
rae Fig. 95) are present, aud two cells are seen delaminating side by side in Fig. 95.

REFERENCE LETTERS.

A, (1), rudiment of first antenna.
A, (IT), rudiment of second antenna. 2
Ab. P., ventral plate. , 5
a C, M., proliferating area of optie Eanglion:
Eet., ectoderm. “A
saat j { Md., rudiment of faanazbie c
Mea wandering cells (mesoblast) attached to ectoderm.
4 0. G., rudiment of optic ganglion.
0. D., optic disk.
s.', 8.2, products of degenerating chromatin.
St. A,, sternal area.
7. Cd., transverse cord uniting optic disks.
¥. C., wandering cell; Y. C.', wandering cell degenerating.

Platé XXXVII.

FH. Herrick, del. ck 8 Wine Langage Ye
ALPHEUS

“Se

ut

b
Foal

Ra G MUS eT hee, (

Pay

ftp eviw

Sw

“*

FS

Be Pana, ie ae

6 : S 7 ie oi = q
F . 2 Bee =F
\ : SBE OED i 8 =e
4 at ne Se
=aee i ; ‘ ao
538 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. | =

Prats XXXVIIL
(Stage VI.)

Fries. 96-97. Longitudinal sections through the embryo shown in, Fig. 93. The more lateral of the
two, Tig. 96, cuts the middle of the optic disk, and shows the large cells of the prolif-
erating area, one of which is caught in the act of dividing. Fig. 97 cuts the inner”
portion of the optic disk and the ventral plate on a level with the budding mandible
(Md.). 295.

Fras. 98-100. Longitudinal serial sections through an embryo six hours older, from the same
batch of eggs. The mouth (Fig. 98, Std.) has already appeared. The mesoblast,
formed chiefly from wandering cells, is well established on either side of the middle
line of the body, and is well seen under the folds of the appendages (Fig. 100, Mes.)
into which it extends. The mesoblast represented by the lower layers of the ventral
plate is still being increased by the migration of cells from the surface of this plate,
as is indicated by cell ec., which is interpreted as a superficial cell about to migrate
(in Fig. 98). In Fig. 100 a cell at the surface of the optic disk is in the act of delami-
nating. Large numbers of degenerating cells and their products are now encountered
(S. C., s.). 295.

REFERENCE LETTERS.

A, (I), bud of first antenna.

A, (IT), bud of second antenna.

Ab., Ab. P., Ad. P., ventral plate.

App., area of appendages.

C, M., proliferating area of optic disk. ¥
ee., ec.', migrating aud dividing cells at surface of ventral plate.
Eet., Ep., ectoderm.

Md., rudiment of mandible.

Mes., mesoderm.

O. C., optic ganglion.

O. D., optic disk.

s., 8, products of degenerating chromatin.

S. C., S. C..~, cells in various stages of degeneration.

St. A., sternal area.

Std., stomodeum.

T. Cd., Transverse sheet of ectoderm uniting optic disks.
Y., Y. S., yolk spheres.

Plate XXXVIZ.

FH. Herrick del.

ALPHEUS

ware Ne

a So
a |
;
ma f _
7 _ —
7 Ju Sr ed
] Q

= ee.

.

Nageayey A> igi hoe

540 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Puate XXXIX.

(Stage VI.)

Fras. 101-105. Serial longitudinal sections of early nauplius embryo, twelve and one-half hours
older than that represented by Figs. 98-100, Pl. xxxvul, and eighteen and one-half
hours older than the stage represented in Fig. 93, Pl. xxxvul. The thoracico-abdomi-
nal fold or papilla is now forming, apparently by the ingrowth of the surface ectoblast
(Fig. 104, Ab. O.). Fig. 102 is exceptionally favorable in showing the undoubted
delamination of two cells standing side by side at the surface of the optic disk (ec.).
The common radial division of the ectoderm of the thoracico-abdominal region
and other parts is illustrated by the cell ec.! of the same section. Fig. 105 cuts
the straight tubular stomodzeum. x 295.

Fic. 106. Longitudinal median section of embryo several hours older than the last. A deep, narrow,
transverse furrow (Ab. C.) now abruptly separates the thoracico-abdominal papilla
from the sternal area lying between it and the stomodzeum. x291. ~

Fic. 107. Transverse section through the optic disks, from same stage. Cell delamination in this
region is again met with. x291.

Fra. 108. Longitudinal lateral section through entire egg, showing the distribution of wandering
cells, and the relations of the embryo to the ovum. The eggshell is unnaturally dis-
tended. An inner molted membrane is present, as is better shown in Fig. 106 and
Fig. 104, Mb.

In Fig. 108 a large cell is Seen at the surface, and below this a large cell followed
by a row of similar cells. The first two cells possibly represent a budding ectoblast
and mesoblast, and the rows of cells at the surface and below it are possibly derived
from them. 115.

REFERENCE LETTERS.

A, (J), bud of first antenna.

A. (IT), bud of second antenna.

Ab., thoracico-abdominal papilla.

Ab. C., transverse superficial furrow by which fold of the thoracico-abdominal process is formed.

A. Y. S., products of degenerating chromatin,

B, Z., budding zone.

Ch., eggshell.

C. M., proliferating area of optic disk. :

Ct. S., cells on ventral side of yolk next to optic disks, probably representing mesoblast derived from
wandering cells.

ee., ec.1, dividing ectoblastic cells.

Eet., Ep., ectoderm.

M., wandering cell at surface behind thoracico-abdominal fold (Fig. 108).

Mb., embryonic molt. ,

Md., rudiment of mandible.

Mes., mesoblast.

O. D., optic disk.

O. G., optie ganglion.

O. S. G., brain.

Pd., proctodxum.

S., S..-°, products of degenerating chromatin.

S. C., degenerating cells.

St. A., sternal area.

Std., stomodeum.

Y., Y. S., yolk.

)

Plate XXXIX.

FH. Herrick, del. asso Wise ibagagtang (ore
ALPHEUS

'¢

Ko

~ 542 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Prats: XL:
Boe (Stage V1.) : =

‘

Fie. 109. Sketch of egg-nauplius. Anus not so clearly seen in surface view, as represented 21) Te Pp
this and the following figure. Mouth on a level with antennules. x72. =o}
Fic. 110. Sketch of older embryo. Appendages all bending backwards and inwards toward |
middle line.” x72. ;
Fia. 111. Egg-nauplius less developed than shown in Fig. 109, but from same batch of eggs.
The position of the mouth, which is post-antennal from the first, is now on the middle —
line between the antenn# and the antennules. The probable position of the anus
is indicated, but it could not be clearly seen. The bud which represents the endop- :
odite of the antenna is just appearing on the right side. 157. | :
Fig. 112. Oblique transverse section, through egg-nauplius of a common shore érab of Beantort,
North Carolina, probably Sesarma. x 286. .

Fig. 113. Median longitudinal section, through a similar embryo. The egg membranes are not
naturally shown. The yolk is diagramatically represented. Wandering cells occur
in it (Y. C.), and in Fig. 113 degenerative products (Deg.) are met with. x 286.

é

REFERENCE LETTERS.

A,, anus,
A, (J), antennal bud. 5 Z
A, (1), antennular bud. . : a
Ab., thoracico-abdominal fold. t F
Ch., eggshell. F : : By: ke
: Deg., degenerative cell products.
= ‘ Ep., ectoderm. 3
fee. Gl., ectoblast of neural plate. wale
: : : H,, mesoblast cells, forming rudimentary heart. — > &
E Hg., hind gut. ae
. Lb., labrum. ; 9
Md., mandibular bud.
Mes., mesoblast below surface, . 2
ais O. G., optic ganglion,
: , O, L., optic lobe. . ane:
ee 0.8. G., 8. O, G., rudimentary brain. $e ike
? Std., stomodeum. : mS
nek Vac., vacuole.
ua Y. C., wandering cells. ‘

Numbers 114-125 mark the planes of the transverse and longitudinal sections represented on Pls.
A, XLI-XLIII. ; :

Plate XL

Fig.110.

--- Mes.
r
“orssn., Mt( 1).

FH. Herrick, del.

ALPHEUS AND SESARMA?

a
Ble

KO's gf 4 lev aad

544

Fries. 114-118. Transverse serial sections of egg-pauplius in stage shown in Fig. 109. Plane of

s a ae
MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

*y
ane

-PratE Gk =

(Stage VL) I “

section indicated in Fig. 111, which is from an embryo a trifle less advanced, The |
lobular condition of the enlarged optic disks is well shown in Figs. 114,115. In |
Fig. 114 a delaminating cell (ec.) at the surface of the optic lobe is cut, andin Fig.
115 a superficial ectodermic cell next the brain is dividing perpendicularly. Ge Ss 4
intimate fusion of the brain and the optic ganglion is seen in Figs. 115, 116. Fig. aon
117 cuts the stomodeum passing through the mouth and the antennze. Mesoblast is —
already well established in the pockets of all the appendages, as indicated at an
earlier period. Degencrating cell products (S., A. Y. S., Fig. 18) are very abundant oho ies
in the region of the stomodeum, and oceur also in the appendages (S.-8.!, 8S. C., Fig. an
118). «291. : a

REFERENCE LETPERS.

A, (J), antennal bud. a . ‘ a)
A, (ID), antennular bud.

A. Y.S., alteration products of yolk. xe wy 7
Ct. S., cells partially covering brain, derivatives from yolk-wandering eells,

ec., surface cell of ectoderm dividing horizontally. ;

Ect., Ep., ectoderm.

Md., mandibular bud.

Md. G,, mandibular ganglion. ©

M. F., median furrow.

0. G., optic ganglion, —

O. L., optic lobe.

Ret., protoplasmic reticulum.

S.S.!, products of cell degeneration,
8. O. G., brain.

Sid., stomodzum.

Vac , vacuole.

Y., ¥. C.,-yolk.

> ‘I

F-H. Herrick, del.

Fig 118.

ALPHEUS SAULCY!.

Plate XZ

546

Fies. 119-1

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

4

Piare XLII. |
(Stage VI.) | ee

22. Serial transverse sections of the egg-nauplius, continued from Pl. xu1. In Fig,
120 a transverse row of cells with large clear nuclei is seen. This is probably a
series of budding ectoblasts and mesoblasts, already referred to. Wandering cells =»
appear to be settling down upon all parts of the embryo. In the thoracico-abdomi-
nal fold (Fig. 122, mu.) the abdominal muscles are already undergoing differentiation Se
out of the mesoblast of the ventral plate. 295. 7S <a

REFERENCE LETTERS,

A,, anal invagination.
A, (II), antennal bud. : >
Ab., abdomen. _ : me.
A. Y.S., yolk undergoing change. ;
B.Z., budding zone. : : Fem,
Det., ectoderm, — = y 0 pe aa
Hq., intestine. Pe Sl
Md., mandible. aS ae
Ma. G., mandibular ganglion, ; eS ake
Mes., mesoderm, 2 : : pias :
M. F., median groove. . mo
Mu., muscle cells. ee te
Mz. (1), first maxillary bud. ; re
s.', products of cell degeneration. = tes
S. C., degenerating cells.

Y., yolk.

¥.C., Y. €.', wandering cells.
Vac., vacuole.

Plate XLIT

E\H1. Herrick, del.

sect 8 Wlaeions Lathapraphung Ca New York

ALPHEUS SAULCYI!.

ae ee Ses es ee ee ee. ae

Pale ta

Puare XLII.
= (Stage VI.) -.

Fias. 123, 124. Completion of series of transverse sections of egg-nauplius. Cells marked Mes.
probably represent endoderm in Fig. 124.. The heart is being formed at about this
time out of mesoblast cells at H, Fig. XL, and the endoderm ee a plate between
it and the central yolk (v, lig. 133). x 295.

Fie. 125. Median longitudinal seetion aes same stage. Compare with Fig. 106. The thoracico- |
abdominal fold is now distinctly directed forward, ani is overgrowing the sternal
area between it and the mouth. The stomodzum isa bent tube. x 295.

Fic. 126. Transverse section, cutting proctodeum. From an embryo of about the same age as

that represented in Fig. 106. 295. =
Fig. 127. Transverse section of embryo and entire egg on level with anus, ahowiee wandering
cells (Y¥. C., ¥. Or i) soba rams a

REFERENCE LETTERS. : ; Ee

A., anal invagination. :

Ab., abdomen. -*
A.Y.S., altered food yolk. :
Ch., eggshell. _ - : d ‘ Pax ;
Ect., Ep., ectoderm. ; ; 4 ; eae:
Gl., ganglionic rudiment. E : ;

H., rudiment of heart. : sa
Hg., intestine. ; ; ;
Lb., labrum, . ; 3 z
Mb., embryonic molt.

Mes., mesoderm. : - My

Mo., mouth. : ae x ;
Pd., region of proctodwal invagination. Shey Fea
8.,8!., products of cell degeneration. a

s. C., wandering cells, probably in early stages of degeneration,
S. 0. G. , rudiment of brain.
St. A., Ciortal area.

> Std., stomodzeum.

: VAS aos

Y.C., Y. C2, wandering cells.

¥Y.8., yolk spherules. —

Vac., vacuole,

Fig. 125,

FE: H. Herrick, del.

ALPHEUS SAULCYI

Plate XLUI

det: & Widnes Ladhoprmsticng Co Seow Vth

Pratt XLIV. oe é

(Stage VII.)

Fra, 128. Transverse section through embryo, in the region of the first maxilla. Nervous system
not yet differentiated from the skin. x 234. .

Iria. 129, Lateral longitudinal section through optic lobe and extremities of antenne. The differ-
entiation between the retinal and ganglionic parts of the eye is very clear. Meso-
blastic cells, representing rudimentary muscles, are seen attached to the body wall.
x 234.

Fic. 130. Surface view of embryo of this Stage, with buds of four post-mandibular appendages
present. The antennz are covered with a hairy exuvium, which was probably
stripped off from the antennules in this preparation. The mouth is concealed by the
labrum, which nearly meets the thoracico-abdominal fold. The anus is situated
nearly at the extremity of the latter, which is slightly emarginated. 137.

fia. 131. Median longitudinal section in the series from which Fig. 129 was taken. x 234.

Fries. 132-135. Serial transverse sections through embryo in similar Stage. The germinal layers,

definitely established in the egg-nauplius stage, are clearly differentiated at this

period. An incomplete layer of elongated cells (probably mesoblastie in origin, com-
ing from wandering yolk cells), Mes., Figs. 131, 132, is seen between the yolk and
the neural thickening, trom which the nervous system is in process of development.

In Fig. 134 rudimentary muscles suspend the stomodzum to the body wall, and in

Figs. 133 and 135 the three germinal layers can be clearly seen. The heart is repre-

sented by the space filled with mesoblast and serum, between the entoblastic lamella

and the ectoblast. x 234,

.

REFERENCE LETTERS.

A.J, first antenna.

A. IT, second antenna.

Ab., thoracico-abdominal fold.

A. Y.S., alteration products of the yolk.
Ect., ectoderm.

End., endoderm,

G. L., rudiment of optic ganglion.
Gl. 4. II, antennular ganglion.
Lb., labrum.

Mes., mesoderm.

Mo., mouth.

Mu., rudimentary muscles.

Mx. I, first maxillary bud.

0. E., retinal portion of optie lobe.
S. 0. G., brain,

Std., stomodzeum.

Plate XLIV.

F: H.. Herrick, del. Sack et & WDetms Labaprgtang Co Merwe Tort
ALPHEUS

ms <
a= AG a i

eae ae
‘a J ;

552 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. ; ¥
PLATE-XLV. .

(Stage VIII.)

od

Fie. 136. Lateral longitudinal section of embryo in stage intermediate between VII and VIII,
represented in surface view in Fig. 110. To this phase also belong Figs. 137, 144,
and 145, Fig. 136 is to be compared with the slightly older embryo in Fig. 129.

Blood cells (. C.) and other wandering cells are here seen settling down upon the
body wall. A wandering cellis also seen nearly in contact with the optic ganglion. x 241.

Fig. 137. Transverse section of embryo in same phase, just behind the level of the first antennz, 4
showing the relations of the wandering cells at this period to the embryo and egg. x 61. i

Figs. 138, 139. Serial longitudinal sections through embryo in Stage VIII. Fig. 138 should be
compared with Figs, 136 and 129. All the ganglia of the nervous system, at least as
far back as the eighteenth segment, are marked at the surface by deep constric-
tions. The gangliaof the nineteenth and twentieth segments are less distinct. The
ganglia of the eleventh segment lie in the angle made by the thoracico-abdominal
flexure. Wandering cells occur in the yolk, but are less abundant, and the products
of cell degeneration, which enter into the general nutrition, have mostly disappeared.

"241, :

Fies. 140-143, Parts of sections taken at various points on the surface of the egg (series to which
Figs. 136, 137, 144, 145, belong), remote from the embryo, to show the réle of certain
wandering cells which reach the surface and represent mesoblast. In Fig. 140 two
cells (ms., ms.') are partially flattened against the surface, but here, as in Fig. 142,
the wandering cell ms. is clearly distinguishable trom the spindle-shaped ectoderm
cell on the left. Compare Fig. 34. x 241.

Fias. 144-145. Serial longitudinal sections through the embryo and entire egg to show the distri-
bution of the wandering cells. Certain wandering cells not yet flush with the surface,
enter into an organ—the dorsal plate (Dp.)—which is characteristic of a later stage
(Fig. 153, Dp.). The strictly superficial cells of the dorsal plate are probably in all
cases ectoblast, and some of the wandering cells degenerate before they reach the
surface ectoblast. ~

There seems to be a general dispersal of wandering cells from the vicinity of the
thoracico-abdominal fold. The wandering cells which appear in this part were taken
from four consecutive sections, including that represented in the drawing. x61,

REFERENCE LETTERS.

A. TJ, first antenna.

A. II, second antenna.

an., lower margin of optic lobe.
A. 8. a., Superior abdominal artery.
B. C., blood corpuscle.

b.m., basement membrane.

ch., eggshell.

Dp., dorsal plate.

End., endoderm.

G, IV-XVIII, segmertal ganglia.
Gl., gangliogen,

H., heart.

hd., hypodermis.

Hg., hindgut.

mes., mesoblast.

mo., mouth.

ms., ms.', wandering cells at surface.
0. L., optic lobe.

Rt., retinogen.

Std., stomodeum.

Th. ab., thoracic-abdominal fold,
y.c., wandering cells,

Plate XLV.

NS
Daw

F-H. Herrick, ded Sac a1 8 Withee ghng Ue few Yar
ALPHEUS

;
iin

554 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES, _ :

Puate XLVI.
(Stage LX.)

Fias. 146-151. Serial transverse sections, through the embryo ot A. sauleyi, at the time when
pigment is first deposited in the eye. In Fig. 146 the developmental history of the
retinal layer is well shown. x 230.

Fia. 152. Nearly median longitudinal section of embryo in similar stage. x48.

Fig. 153. Sagittal section of similar embryo, showing degenerating elements in yolk below dorsal
plate. x58.

REFERENCE LETTERS,

A.J, first antenna.

A. IT, second antenna.

Ab., abdomen.

B. C., blood corpuscle.
B.S., blood space.

cp., carapace,

Deg., degenerating cells. -

Dp., dorsal plate.

End., endoderm.

Sfy., foregut.

fs., fiber mass of nervous system.
g. II-III, brain.

g.¢., ganglion cell.

g.m.a., anterior gastric muscle.
H., heart.

hd., hypodermis.

Hy., hindgut.

Lb., labrum.

Md., mandible.

Mes., mesoblast.

Mu. f., flexor muscle.

ocm., esophageal commissure.
0.g., optic ganglion,

0. L., optic lobe.

pk., punct substanz.

pr., perineurium.

Kt., retinogen.

S. 0. G., supra-wsophageal ganglion. ’

T., telson. 3
Tc., transverse commissure.

Th., thorax.

Vac., vacuole.

y., yolk,

¥.C., wandering cells.

dhe

Plate XVI.

F-#f Herrick, det.

ALPHEUS

556 MEMOIRS OF THE NATIONAL

Puate XLVII. a = ee

(Stage IX.) 5 Pate

Pies, 154, 155. Transverse sections through entire embryo of Alpheus saulcyi. In Fig. 154 a yolk oar ¥
nest is cut. Blood spaces occur near the surface of the egg. x61. 2 Si

Fic, 156. Cell nest, containing degeneration products. Its position in the yolk is shown in Fig. : 5

154. x 245. pe

Fie. 157. Part of median longitudinal section through the thoracic-abdominal flexure. The grow- : ake

ing endodermal epithelium and its fusion with the lining of the intestine are particu. Bary

larly well shown. Wandering cells appear to be uniting with the endoderm. »x245.
Fic. 158. Sketch of egg embryo, Alpheus saulcyi, of same phase as that represented by Fig. 157.

x 61. " ; g
Fic. 159. Horizontal section through brain and eyestalks of a slightly older embryo. x61. <j
Fic. 160. Part of transverse section of similar embryo on level with the mandibles. 245. f
Fig. 161. Superticial part of section of egg, showing surface cells, blood corpuscles, and a wander-

ing cell on the edge of the blood space. x 245. é

REFERENCE LETTERS.

A.J, first antenna, a
A, 1J, second antenna, — Sa,
Ab., abdomen. s
dor., aorta. 2 ; = *
ay. 8., granulated yolk products, : : ae a |
B.C., blood cell. : : 3
B.S., blood space. i . Y
Ch., eggshell. ;
cp., carapace.

Deg., products of cell degeneration. : “eo
Het., ectoderm. A ; i
End., endoderm,

Js., fiber-substance of nerve cord,

G.IV, gauglion of mandible. - —
ge., ganglion cell,
gf. fiber ball of second antenna. 3
H., heart. -
hd., hypodermis. 3
hg., hindgut. ; i
If., lateral fiber-mass of brain. ad
Md., mandible. = See |
Mes., mesoblast. =
Mu., muscle cells.

Mu, f., flexor muscle.

Mts., metastoma. é Rn ee
n.¢., neural cord. : - zo: |
O. G., optic ganglia. atl
of., optic enlargement. 7 ead
p.e., pillars of carapace. =
p-Y., perineurium,
p.s., pericardial sinus,
Rt., retinogen,

Sid., stomod#um.,

vac., vacuole,

y.¢., wandering cell.
y.u., yolk nest.

Plate XIVII

FH. Herrick, del.
ALPHEUS

zy
chase

~~ e

ae

~
!

;
"
ry
cs

558 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Puate XLVIIL.
(Stage X.)

Fias. 162-165. Parts of serial sections through the region of the heart and thoracic-abdominal
fold to show the extension and relations of the endoderm. x 57.

Fies. 166—167. Parts of serial transverse sections of the embryo of Alpheus saulcyi. 125.

Fic. 168. Median longitudinal section through a slightly older embryo, showing the ventral
endodermic fold (/), the foregut still screened from the yolk, and the nervous
System separated from theskin. » 227.

REFERENCE LETTERS.

Ab, abdomen.

Ab. 9. J, first abdominal ganglion,

aor., aorta. . 3

B.C., blood cell. !

B.8., blood space. ’
ce., crystalline cone cells,

Deg., products of degeneration.

Eep., proximal retinular cells.

End., endoderm.

f., ventral endodermice fold.

g-m.a., anterior gastric muscle,

H., heart. >
Hg., hindgut.

imb., intercepting membrane,

mg., Mesenteron.

mo., mouth.

mpgT, first maxillipedal ganglion.
Mu. E., extensor muscles,

Mu. f., flexor muscles.

O. G., optic ganglia.

p.8., pericardial sinus.

Rt., retinogen.

S. O. G., supra-cesophageal ganglion.
T., telson.

Th., thorax. ; M
Th. g. I, ganglion of first ambulatory limb.

y-¢., wandering cells.

Plate XLVI

‘ en é </ ~~
tof SOS
D S

pe >.
(d

Eo,

\S
(
V

g)
=

5
ry)

CU a. G Ow
NC YQ

F-H. Herrick, del
ALPHEUS

mere ;
: att
fA

‘MEMOIRS OF THE NATIONAL ACADEMY or

‘ot

Puate XLIX. ahs ie aa.
_ (Stages X and XIL) ie ea a

; - Se
Figs. 169-173. Parts of serial transverse aéetions through the embryo of Alpheus Sint: in Stage
X. In Fig. 173 the reproductive organ KR. O. is cut. x129, (Fig. 173, x 234.)

my

: Vic. 174. Horizontal section through nervous system of the first larva, on a level with the eaaphaee
eae geal commissures. 234. >
“= Vias. 175, 176. Transverse sections through the neural cord of the first larva. In Fig. 176 th ans

transverse commissure of the ganglie of the tenth segment is eut aud aim ne es 9%

aes sectioned. x129. | : >,

REFERENCE LETTERS. “

= . AT, first antenna, -

aN : : : 2 A. II, second antenna, =

aie ‘ b., abdomen. +

ee —_ag., antennal gland. : . :

\ B.c., blood corpuscles, 3 ers:
—B.S., blood sinus. : s eye. aks

Br., branebia.
cp., carapace. : vite aye Se
End., endoderm. : ; JS hig pee
Jq., foregut. z j , oo ;
g.¢., ganglion cell. y . — PRON eee! AAR ee
Had., hy podermis. Y : aA ss
as hindgut. , an Ces
1. f., lateral fiber-mass of, brain. a ign
Md., vase of mandible. < Sees et
Mes., mesoderm. z Bes be te aed
Mg., wesenteron. . : FROME Sav oh LP
Mu., muscle. xs
: Mu.e., extensor muscles of abdomen. — en : -
Mu.f., flexor muscles of abdomen. =, Zz bs ane
Mzx., base of maxilla. . , ; pes
Muepd., base of maxillipeds. ; af V4 -g re
n.c., neural cord, . a
of., optic fiber-mass of brain.
0.9., optic ganglion,
Pr., perinearium. bat, ete
k, O., reproductive organ. : Ee Sic Sie
80g.) DEIN. se : and pasa Hat
t.c., transverse commissure, ; x eee:
y.c., Wandering cells, : ee Pa

Plate XLIX.

FH. Herrick, del.

ALPHEUS

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. — |

Prare =; s

(Stage XL.) , 1 ate as

Fes. 177-179, 181, 182. Serial transverse sections of the embryo of Alpheus heterochelis, whieh i is
nearly ready to hatch. The shell is somewhat diagramatically represented and appears =
thickened in Fig. 182, owing to a coagulable substance beneath it. The cells rep-
resented in the yolk in Fig. 182 appear to be endoderm cells, which have become 2
mechanically detached from the walls of the mesenteron. x 74. e

Fic. 180. Nearly median longitudinval section through a similar embryo. The endodermal lining =

ri: of the mesenteron is not yet nearly completed. x 74. f s i :

REFERENCE LEWTERS. : Ae

Ab., Vi, ganglion of sixth abdominal appendage.
ag., antennal ganglion,
ans., anus. =
ch, ex., external ene f
ect., Sctiee 7
end., endoderin, ‘ ; he
JSq., foregut. : ; BE Xn 2
gma., anterior gastric muscle, =i: ‘
H., heart. ; Pa Si SE eae
hg., hindgut. 3 : , rian goog he's
hy., Ly podermis. ~ Se yd ey
1f., lateral fiber-mass of brain. \ Fy, hoe
mg., mesenteron. + Sw ye,
mg.! mg? of other figures, posterior lobe of midgut. ‘ ; ; ear
mu. f., flexor muscles of midgut, pine
mu. é., extensor muscles of midgut. Per eee ; meee
~ oem., esophageal commissure. ‘ ss 4
o. pd., optie peduncle, ; ; 4 . *
Ret., retina.
soq., brain. > : ss
T., telson. : ease, 08 gat
1-4, ganglia of eye-stalk.

.

Plate L..

FH. Herrick, del.

2.01 8 Wtaetns Labographeng Ce. Mew York

ALPHEUS HETEROCHELIS.

Phare. Bs? ee eae oe ee
: | aes (Stage XI.) j epee) ory,

Figs. 183-186. Continuation of series of transverse sections of embryo beeun on Plate ve x4

Fic. 187. Part of sagittal section of similar embryo, cutting eyestalk somewhat obliquely. Th

/ specimen was depigmented in nitric acid. The distal retinular cells, occupying the _ *
spaces (P9.c.) between the peripheral ends of the cones, are not represented. x 305. Pork

REFERENCE LETTERS. \- Ae ei

~ ac. P., accessory pigment cells. a “! ye eh
ad.m., adductor of mandible. ‘ aL ‘ Cnty ey
a. 80., eee abdominal arter y- MG q é
> bg., branchiostegite. “ ; = ~

b.v., blood vessel. : Pay ce
(ees crystalline cone. : 1 ara
eg., corneagen. , “es, ORE
ect., ectoderm. | LAr)
ey 4 end., endoderm. — : saan Say iat sa Sat
\ ; : f9-, foregut. : bod Sa ee ed
1 R #., heart. : ey et eS ee
A hy., hypodermis. : 3
imb., intercepting membrane. ‘ ea Sets
mg., midgut. es | : Mice ees
ing.®, posterior lobe of midgut. g : fee
Mu., muscle of eyestalk. = ' 4 poe
Mu. e., extensor muscles of abdomen,
Mu. f., flexor muscles of abdomen. Si SAN Alnor
0.¢.m., esophageal commissure. = ee
i : Pq. C., position of distal retinular cells. etek
Ps., pericardial sinus. ie cet
Rtu., proximal retinular cells. Oy Mer, :
Rtu.', nuclei of proximal retinular cells. Seg e
3, 4, ganglia of eyestalk. (ft

2
i *

Ped ee ee a Se

Plate LI.

Sachets 8 Wilber Ltbegrapneng Co. Mew York

FH. Herrick, del.
ALPHEUS

-

ie

MEMOIRS OF THE NATIC NAL ACADEMY OF

= if

‘ ia PLATE Tse

a2 Fias. 188, 189. Parts of transverse serial sections front the embryo of Baleannates vulgaris, 2 a
+e. _ the stage when pigment is just appearing in the eyes. In the anterior Bestion (Fig.
188) the retinogen is a unicellular layer. 305. = rahe
Fias. 190-191. Parts of serial transverse sections through the brain, the optic ganglia, : and eye. of."
an embryo of Alpheus heterochelis. In the anterior section (Fig. 190) the clusters (8) nef
cells which represent the ommatidia are well shown. Numerous eaneuee cells are ace
dividing. x305. : =. aa tales
Fic. 192. Part of transverse section through eye, optic ganglion, and brain at a later stage x 305, —

REFERENCE LETTERS. : ‘ é Pits hehe

A.J, first antenna. : iy

Ab., abdomen. : cae i Phy a's
ce., erystalline cone cells, ; : :
imb., intercepting membrane, ‘ “.
mes., mesoderm. Paty ee
Ret., retina. é ‘ TEN
rtl.’, rudimentary eighth proximal retinular cell,

8og., brain.

T., telson, “ ' re
X., stratum of large ganglion cells. ; : t
1, 5, 4, proximal, external mda and distal peenenia of optic ganglion, ;

Plate LI.

Fig. 189.

AL GpVORG a.
AU \ pee,

FH. Herrick, del.
ALPHEUS AND PALAEMONETES.

Pe | TA ee

ay et
—

v

568

Fic. 193.

Fia. 194.
Fie. 195.

Fic. 196.

Fie. 197.

Fie. 198.

Fie. 199.

MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES.

Prats LET

Part of transverse section through an embryo of Alpheus sauleyi, which is nearly ready
to hatch, showing the third left branchia covered by the branchiostegite. x 289.

Part of sagittal section of eyestalk of a slightly younger embryo. x 289.

Part of transverse section, showing branchia, of the third larva of Alpheus sauleyi (twenty-
four hours old). x 289. £

Nearly median longitudinal section of first larva of same. The anterior lobes of the
midgut (mg') still contain unabsorbed yolk. Compare Pl. xxi, Fig.1. x58.

Part of transverse section, showing the papilla, which bears the median eye in the first
larva of same. x 289.

Transverse section of first larva, cutting the lateral fiber balls of the brain, the anterior
lobes of the midgut, and the green gland. x 289.

Part of transverse section through an advanced embryo of Alpheus sauleyi, parasitized
by a fungus, most of the cells of which are encysted. From brown sponge, Abaco,
Bahama Islands. v, Appendix II. x 186.

ab., abdomen.

Ab, VI, sixth abdominal appendage.
acp., accessory pigment cells.

ag., green gland.

ag.s., end sac (?) of gland.

as. d., Superior abdominal aorta.
bg., branchiostegite.

b. s., B.S., blood space.

br., branchia of third left ambulatory limb.
ce., crystalline cone cells.

eq., corneagen.

el,, lens.

co., crystalline cone.

cs., c8.‘~, cysts of parasite.

es.°, smaller, naked cells of parasite.
g.+°, segmental ganglia.

gf., tiber-mass of second antenn:e.
gma., anterior gastric muscle.

H., heart.

Hd., hy podermis.

Hg., hindgut.

Lb., labrum.

l.c., longitudinal commissure,

mg., midgut.

REFERENCE

LETTERS.

mg.', anterior lobes of midgut.
mg.*, lateral lobes of midgut.
mg.*, posterior lobes of midgut.
mo., mouth,

ms., masticatory stomach.

mu. é., extensor muscles of abdomen.
mu. f., flexor muscles of abdomen.
n.¢., neural cord.

oc., ocellus,

oe., esophagus.

O.G., 0.g., optic ganglion.

of., optic enlargement of brain.
op., ophthalmic artery.

ps., pericardial sinus.

pr., perineurium,

f., rostrum.

Ret., retina.

rtl., nucleus of proximal retinular cell.
sog., brain.

Sp., parasitic growth.

St. s., sternal blood sinus.

T., telson.

y., yolk.

Plate Lil

FH. Herrick det.

ALPHEUS

Puate LIV.

Fic. 200. Ommatidium of eye of small adult Alpheus Sea (from brown sponge) ; pigment. removed |
by nitric acid. x 294. “

Fics. 201-204. Transverse sections through four wajacant ommatidia of first eae ofsame. In Fig.
201 the corneagen is cut, and in Fig. 202 the nuclei of the cone mother cells. In Fig.

“204 the rhabdom is sectioned and the seven proximal retinular cells. 294. |

Fias. 205-208. Transverse sections through adjacent ommatidia of the adult eye, taken at various
levels. Fig. 205, the deepest section, shows the peculiar seven-pronged figure of the
rhabdom. The proximal retinular cells appear in sections, asif fused together. x 294.

Fies, 209-211, Transverse serial sections through the first larva of Alpheus saulcyi. x74.

REFERENCE LETTERS.

A. TI, first antenna.

A, II, second antenna.

a. cp., accessory pigment cell.

ac.pn., nucleus of accessory pigment cell.
ao., ear.

Bm., intercepting or basement membrane.
ce., crystalline cone cells.

¢g., corneagen.

el., lens.

Co., co., crystalline cone.

emb., cone membrane.

hd., hypodermis.

me., membrane of distal retinular cells.
nf., nerve fibers.

oc., ocellus,

og., optie ganglion.

of., optic enlargement of brain.

pap., papilla of ocellus.

p.g.¢., distal retinular cells.

X., rostrum.

Rb., rb., rhabdom.

Ret., retina,

rtl., proximal retinular cells.

Plate LIV.

F-H1. Herrick, det. Sect d Wikchanegryting Ca Rew Te
ALPHEUS

; . bN Rat

MEMOIRS OF THE NATIONAL ACADEMY OF

od

PLATE: GV " oor
pes : (Stage XI1.) seers ; oie

Fics. 212-223. Transverse serial sections of the first larva of Alpheus sauleyi from Joes same indi-
vidual as Figs, 209-211, excepting Figs. 222, 223.- shag

REFERENCE LETTERS. ; pean es

A. II, second antenna. - oe PoRe j ‘
ad. m., adductor of mandible. ee ' -
ag., green gland. : Eres aon
af., antennular fiber- -mass of brain. 4 a
ao., ear. ‘ sees Wy 2) Te ;
a. op., ophthalmic artery. : , ; yrs
Bg., branchiostegite. ~ : i: ”;
B.gl., gland-like body. — OA ce 4
B.S., blood sinus. - 2 ae ; Pic atlea ant
Sy., foregut. ; 3 ah SA ge oii ae te
So., fiber-mass continued into esophageal commissure. 2 eee a
gf., antennal fiber-mass. 3

gs., lateral pouch of masticatory stomach, ‘ and
Lb., labrum. x ; = Agee
lf., lateral fiber-mass of brain. a
Md., mandible. ~
Mg., midgut.

Mgq'., anterior lobe of midgut. er
Mg?.. lateral lobe of midgut. 5

Mp., septum between anterior lobes of midgut, ‘ = nase
M.S., masticatory stomach.
Mts., metastoma.

Me. T, first maxilla.

Mupd. I, first maxilliped.
n. ag., antennal nerve. : nose

n.an., antennular nerve.

0c., ocm., «esophageal commissure.

of., anterior fiber-mass and transverse commissure of brain.
p. V., pyloric valve of masticatory stomach. —

st. s., sternal sinus.

‘

Plate LV

F-H. Herrick, del.

FIRST LARVA OF ALPHEUS SAULCY!.

ov
MEMOIRS ov THE NATIONAL Ac EM OF

Prate LVI.
(Stage XI. My

REFERENCE LETTERS.

Ab. V, fifth abdominal appendage.
a.i.a., inferior abdominal aorta.
a. op., ophthalmie artery. ~
a, 8, @., Superior abdominal artery.
bg., branchiostegite.
br., branchia of ambulatory appendage.
B.S., blood sinus.
gg. ©, middle, ventral, and dorsal lobules of posterior lobe of midgut.
25 Be hear ‘
hg., hindgut.
hy., hypodermis. R
le. th.-ab., longitudinal commissures uniting last tee with first abdominal ganglia. a 3
_ Mq., midgut. is
Mg. *, lateral lobe of midgut.
Mq.*, posterior lobe of midgut.
Ms., masticatory stomach.
Mu.e., extensor muscles of abdomen.
Mu, f., tlexor muscles of abdomen.
Mrpd. I-III, first to third maxillipeds,
pleu., pleuron.
ps., pericardial sinus,
Th. I-V, tirst to tifth ambulatory limb.

3

Plate LV1

ala.
F:H. Herrick, del.
FIRST LARVA OF ALPHEUS SAULCYI.

:

DP eal

by sre

Pirate. LVI.
(Stage NTL).

_ Fias. 236-245. Horizontal sections of first larva, jNoacebag: further the penctomy Be. the limen
tary tract and the nervous system. x 57.

REFERENCE LETTERS.

A.J, 11, first and second antenna.
ag.. green gland.
af., antennular fiber-mass.
a0., ear.
bg., branchiostegite.
Pnd., endoderm.
Jy., foregut. :
Jo., fiber-substance of wsophageal commissure,
gf., tiber-mass of second antennz.
gg-'~*, middle, ventral, and dorsal divisions of pouiesion lobe of midgut. :
hg., hindeate :
/f., lateral fiber-mass of brain.
Md., mandible.
Mq., midgut.
Mq.', lateral lobe of midgut.
Mp., partition between anterior lobes of midgut.
Mts., metastoma,
Me. I, I, first and second maxille.
Mxpd. I-LII, first to third maxillipeds.
‘n.an., antennular nerve.
n.¢c., ventral nerve-cord.
of., anterior fiber-mass of brain.
og., optic ganglion.
Ret., retina, t
Th. I-V, first to fifth ambulatory limbs,
y., yolk.

Plate LVI

FIRST LARVA OF ALPHEUS SAULCY!.

*

, :
* 4 zy a
v

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