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HARVARD COLLEGE-LIBRARY 

OIFTOF 

DANIEL B FEARING 

CLA.55 OF1882 -AM 1911 

OFNEWPORT 

1915 

THIS B^K 15 NOT TO BEHOLD OR EXOIANGED 



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LOBSTERS: Brooks, W. K , fit ffcrrick, F. H. 
The Embryolugy and Metamorplioris of the Mac- 
Toura. 57 colored platos. 225 p\r, 410, buckrarn. Wash- 
ington» iB^J. 4tii Memoir National Acad. of 
Science * * S J.on 



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"i.^c. 



NATIONAL ACADEMY OF SCIENCES. 



VOX,. V. 



FOURTH MEMOIR. 



THE EMBRYOLOGY AND METAMOKPHOSIS OF THE MACROURA. 



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5l8T Congress, ) SENATE. ( Mis. Doc. 

2d Session. S I No. 94. 



MEMOIRS 



OF THE 



NATIONAL ACADEMY OF SCIENCES, 



Volume 'V. 



WASHINGTON: 

OOVEENMENT PBINTINQ OFFICE. 

1891. 



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.« 
1 

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THE 



EMBRYOLOGY AI^D METAMORPHOSIS 



OF THE 



MACEOURA. 



BY 



^W. K. BROOKS, 

PROFESSOR OF ANIMAL MORPHOLOGY IN THE JOHNS HOPKINS UNIVERSITY, 



AND 



PROFESSOR OF BIOLOGY IN ADELBERT COLLEGE, 
l-ATE FELLOW IN THE JOHNS HOPKINS UNIVERSITY. 



WITH FIFTY-SEVEN PIjATES, 



8. Mis. 94 21 



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f s a I 5. 5 



HARVARD COl \ ^QE UIRARY 

DANIEL li. rEARIN6 
MJUNEItIi 



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CONTENTS. 



I. Introdaction. 
11. The life history of Stenopns hispidos. 

Section 1. Nataral history of Stenopus. 
Seotion 2. Segmentation and the early stages. 
Section 3. Metamorphosis of the larva. 
Section 4. The adnlt. 
Remarks. 
List of species. 
Literature of Stenopns. 

III. The habits and metamorphosis of Gonodactylus chi- 

ragra. ' 
Section 1. The struetare and habits of the adnlt. 
Sections. Metamorphosis. 

IV . The metamorphosis of Alpheus. 

Section 1. The metamorphosis of Alpheus minos. 
Sections. The metamorphosis of Alpheus hete- 

rochelis in 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 
saulcyi. 
y . Alpheus : A study in the development of the Cms- 
tacea. 
lutroduction. 
Methods. 
Part First. 

Seotion 1. The habits and color variations of 
Alpheus. 



Part First— Continued. 

Section 2. Variations 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. Measmrements. 

Section 7. The causes and significance of varia- 
tion in Alpheus saulcyi. 
Part Second. 

Development of Alpheus. 

Section 1. Structure of the larva of Alpheus 
saulcyi. 

Section 2. The origin 6f ovarian eggs in Alpheus, 
Homams, and Palinurns. 

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 wandering 
cells in Alpheus. 

Section 8. The development of the nervous sys- 
tem. 

Seotion 9. The eyes. 

Section 10. Summary. 

Section 11. Refereifces. 
Explanation of figures (accompanying each plate). 



[With fifty-seven plates.] 



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CHAPTER I. 
IHTBOBTJGTIOH. 



By W. K. Brooks. 



$ 

No great groap of animals is more favorable than the Orostacea for the stndy of the history 
and significance and origin of larval forms, for these animals possess a number of pecaliarities 
which serve to render the problem of their life history both annsnally interesting and significant, 
and at the same time nnnsnally intelligible ; nor are these pecnliar 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. As a 
result, ftom the very tature 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^rthropods 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 the 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 steps in 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 Orustacea, but another consideration, 
the fact that, with few exceptions, the higher Crustacea are marine, renders the problem of their 
life history much 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 i)ersistency of those external conditions to which the larval stages were originally 
adapted. 

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



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326 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 

sarroand a modern terrestrial larva mast, in nearly every case, be very different from tbose under 
which the remote ancestors of the species passed their life, bat while this is also trae, 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 snrroundings of marine 
animals take place mach more slowly than corresponding changes on land. 

This fact, joined to the definite character of the changes which make np 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 Clans has clearly proved that adaptive larval forms are much 
more common among the Decapods than had been supposed, his writings and those of Fritz Mnller 
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 provii}^ this so clearly. Clans' 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 Macronra, and this work has 
been prosecuted at every opportunity up to the present time. Some of my results have been pub- 
lished in my monograph on Lucifer, in the Phil. Trans. Boyal Soc. for 1882, and others are incor- 
porated in my report on the Stomatopoda collected by H.Jtf . S. Challenger. 

This memoir contains the life histories of a number of additional species based in part 
upon my own studies at Beaafort, 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 Macronra, 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 ^^Alphetts^ 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 Stenopns 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. 

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 Macronra which, like Peneus and the Ser- 
gestidae, have retained the primitive or ancestral metamorphosis, and that its secondary modifica- 
tions are very slight as compared with those of ordinary macrouran larvae, and also that the 
Beaufort larvae are new to science. (See Pis. ix and x.) 

These larva3 have the full number of adult somites and appendages, and in side view they are 
very suggestive of the Sergestidae. They are very much larger than ordinary pelagic larvae and 
are quite different from any known forms of Macronra. 

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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MBMOIES OP THE NATIONAL ACADEMY OF SCIENCES. 327 

middle line and are then swept backwards and outwards, describing at each stroke a circle equal 
in diameter to about twice the ♦ength 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 freshwater 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 Stenopm hispiduSj 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 is 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 Inale and a female swimming together side by side and exhib- 
iting evidence of strong conjngar 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 i>rinciples, 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 and vague 
adaptation to many conditions. 

Its antennae are unusually long and slender, and the acoteness of its senses, together with its 
very remarkable alertness; the quicf ness with which it perceives danger, and the rapidity with 
which it escapes; have undoubtedly 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. ^ 

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 sometime be found upon the Atlantic coast of 
our Southern States, there is no evidence that this is the case, and the larvae 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 larvae 
'had therefore Pandered 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 
Hevrick 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 ^ 

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MEMOIRS DP THE NATIONAL ACADEMY OF SOIBNOBS. 



nuclei, and so on until the number is very great. As this process of division goes on the nuclei, 
each with an investing layer of protoplasm, gradually migrate t(f 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 outlines 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 croi;^ded, 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 general, with 
individual peculiarities in which it differs from all of them. 

At the time of hatching (PI. vii and PI. xi, Fig. 26) ft has sessile eyes, locomotor antennsB, 
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 ordinary 
macrouran (PI. viu). 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 antennse are shortened like those of a zoea, and the maxillipeds become the 
chief locomotor organs. 

As these larvae could not be reared in captivity the later stages were studied from captive 
specimens, but Professor Herrick ha» proved that the Beaufort larvae are either young Stenopi or 
else the larvae 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. xii). 
It is in the Mastigopus stage, with greatly elongated eyes, and with antennae which are gradaally 
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 Sergestidae, the fest two ^airs of "walking legs" are shed after 
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 shortening 
of the eyes and the reacquiiition of the fourth and fifth pereiopods. 



ALPHBUS. ^ 

The genus Alpbeus 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 coral 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 (PL* 
I, II, and IV). 

Nearly every mass of sponge or algae or of coral rock or living coral which is fished up from 
the bottom and broken to pieces contains specimens of one or moje 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 npon 



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MEMOmS OF THE NATIONAL ACADEMY OP SCIENCES. 329 

the bultcui iu shallow water. Occasionally tbey inhabit short, vertical barrows, which they con 
stract for themselves in the sandy mad, bat most of the species pass their life hidden in the shelter 
which they find upon the reef. 

The most conspicaoas characteristic of the genas is the great enlargement of the claws of the 
first pair of walking legs. Both claws are large, bat one of them is enormous, and it serves as a 
most formidable weapon of ofiense and defense. In some species this large claw nearly equals . 
the body in size, and K; 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 kegt 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 maji. 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 
^nd rounded, and the animal advances warily to the attack with the claw widely opened and 
stretched 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. i 

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 laJ)oratory 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 deala 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. Eggs 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 si>ecies, the individuals of a single species sometimes differ more from 
each other, as regards their metamorphosis, than the individuals of two very distinct species. 
This phenomenon has been observed by us and carefully studied in two species — Alpheus hetero- 
chelis AiidAlphejis «awteyt— 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 r 

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330 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 

• • 

of larval stages, the life history of those which are foand at Key West is very different from that 
of those which live on the coast of North Oarolina, while those which we studied in the Bahama 
Islands present still anothier 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 that of those which inhabit the other. In this species the adults flso are different from 
each other, but as we found a perfect series of transitional forms there is no good reason ^r 
regarding them as specifically distinct, and in the c^ of the other species — Alpheus heteroohelis — 
we were unable, after the most thorough and minute comparison, to find any difference whatever 
between adults from North Oarolina and those from the Bahama Islands, although their ^fe histones 
exhibit a most surprising lack of agreement. In fact, the early stages in the life of Alpheus hete- 
roehelis in the Bahama Islands differ much less from those of Alpheus minor or Alpheus narmani 
than they do from those of the North Carolina Alpheus Keterochelu^ and, according to Packard, the 
Key West heteroohelis presents still another life history. 

In the summer of 1881 1 received the American Naturalist with Packard's very brief abstract 
of his observations at Key West upon the development of Alpheus heterocheliSj and read with great 
surprise his statement that this species has no metamorphosis, since, while still inside the eggj 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 larvae 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 illnstra* 
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 diversify 
between the larvaB 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 its conditions of life chiefly affects 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 larvse are, as 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 ns 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 larvae 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 samf relation may also bo exhibited when the 
larvae of one species of a genus have become adapted to a mode of life very different from that of 
the larvae of the other species of the genus. Thus those si>ecies of ^ginidae whose larvae are para- 



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MEMOIBS OF THE NATIONAL ACADEMY OP SCIENCES. 331 

sitic multiply asexually daring the larval life and build up complex communities, while nothing of 
the sort occurs in those species with free larvae. 

Many similar cases might be given, but we must bear in mind that they are all very different 
from t^le one now under examination. In ali such cas<is the difference is between the larvae of two 
distinct species, wliile in Alpheus we have a similar difference between the larvae of individuals of 
a single species. 

Among other animals it is not very unuaual 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 foruuof 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 larval 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 distinct 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 that 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 PI. xvi, 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 antennae 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 PI. xvi, Fig. 1, 
and PI. XVII, 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 api)eared, 
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 rudimentary. 

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, which 
projects beyond the tips of the antennae. 

After its third moult the larva passes into the fourth stage, which is shown in PI. xviii, 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. ^ 

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332 MEMOIRS OF THE NATIONAL ACADEMY OI* 80IBNCB8. 

After the fonrth moult the larva passes into the fifth larval stage, when it resembles Fig. 1 of 
PI. XXI, so far as concerns the anterior end of the body, from which it differs greatly as regards 
the telson and nropods. 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 foor 
thoracic limbs. The first five pairs of abdominal appendages are now represented by bads, like 
those showQ in PI. xxi, Fig. 1, bat the telson and nropods are nearly like those of Fig. 3, in PI. 
XX. The telson is narrow and much elongated, and its marginal spines are very small. 

Daring the moults which follow, the abdominal appendages become fully developed, the eyes 
become completely covered by the carapace, the antennule develops a scale, the antennsb 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 PI. xx. Fig. 2. 

This life-history is common to Alpheus minor at Beaufort and New Providence and Alpheus 
nommni and Alpheus heteroehelis at New Providence, although the lattef species presents a totally 
different life-history at Beaufort Before it hatches, this form, as shown in PI. xx, Fig. 1, reaches 
a degre^ of development which bears a general resemblance to stages two and three of the Bahama 
form, with certain differences which are pointed but in the sequel. 

Immediately after hatching it assumes the form which is shown in PI. xix. 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 x>ower of locomotion. The first moult occurs in a few hours, 
and the larva assumes the form shown in PI. 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 PI. xx, Fig. 2, and a still older one in PL xvii, 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 heteroehelis has, at first, three, then four, then five, and then 
seven fully developed and functional exopodites, while the North Carolina 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, is more advanced than the fourth larval stage of the Bahama form, 
while the nropods 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, and 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 occu^ 
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. sauloyi, although Qu6rin'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 PI. xxi. Fig. 1. It 
has rudimentary gills, the eyes are imperfectly covered, the antennules and antennae are beginning 
to assume their adult form, and the exopodites of the three pairs of maxillipeds are the 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 PI. xxi, Fig. 2. The 
eyes are more completely covered, the antennules and antennae are elongated, the thoracic limbs 
have the adult form and the pleopods are all functional. 

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



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MEMOIBS OP THE NATIONAL ACfADBMT OP S0IBNCB8. 



333 



shown in Fig. 1. The following notes on the variations in the coloration and habits in Alphens, 
particularly in A. saulcyiy are taken from a paper by Mr. Herrick published in the Johns Hopkins 
University circulars. ^ 

VARIATIONS IN THE HABITS AND COLORATION OP ALPHEXJS. 

♦ 

Some of the species of Alpheus are usually or even universally found living as parasites within 
the water tubes* of sponges, and it is extremely interesting to find that individuals of the same 
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 on(^ on the 
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 
large specimen. These animals vary from one-eighth to three-fourths of an inch in length. They are 
nearly colorless, excepting the large chelsd, 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 attaclied 
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 to 
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 fix)m 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 flnd a single pair of 
Alphei which resemble those living in the brown sx>onge in most particulars, although they differ from 
them in several Important points. They are distinguished by their large size, and by their peculiar 
and very uniform color. They vary in length from two-thii-ds to one and twotthirds 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 
vermilion-orange (PI. rv). 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 green 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, 
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 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. 



HftbitatofAlpheoB. 


Lenf^of 9 


Number of 


Diameter. 


Color. 


Color of adult. 


Brown sponge 

Green sponge 


InehM. 


19 
347 


InehM. 


YeUow (variable). 

Usaally green; in this 
case yellow. 


Large chelso, red, blue, 

or brown. 
Large ohelad, always 

oraDge-red. 



These two forms, apparently distinct, are seen however, by closer examination, to belong 
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. 
The rostrum usually has three spines, but occasionally only two are'present, the median one being 
lost. It is evident that these animals are perfectly protected from outside enemies while within 
the tortuous mazes of the sponge, as their numbers would show. Parasites such as Isopods, how- 



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334 MEMOIRS OP THE NATIONAL ACADEMY OF 80IEN0ES. 

ever, are not uucominon. There has thas been no chance or need for natural selection to act along 
the line of color. On the other hand, possibly, the Alpheus of the green sponge does re(]iiire 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 tti^ 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 ree^ and may have a protective 
significance. This evidence, however, is not very reliable. 

The colors of certain drustacea, 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 Jiecterochelis 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 
wa3 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 probably 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 t<ponge, 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 fonns, 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 brewn variety that any small or undersized individuals occur, while a single iiair, 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 UMBBYOLOGY OF ALPHBUS. 

At my suggestion Mr. Herrick undertook, in 1886, the study of the enibryology of Alpheus, 
and devoted a considerable part of his time for three years to this subject, and while he carried on 
the work under ray 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 musl 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 G&rolina, and the eggs of the two species of Alpheus 
which occur there were carefully examined and preserved for laborato?:y 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. 



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MEMOIES OP 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 spelcific differences in development, and 
four species were studied exhaustively, in detail. These four are Alpheus heterochelisy Say ; A. mi- 
nusy Say; A. saulcyi, and the Bahama heterocheli^. 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 J which will be referred to separately. 

This prawn has proved to be a good subject in which to study the^ origin and r61e 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 th^ 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 ai>ex 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 
eggy while it still continues and perhaps is accelerated over the remaining portion of it. Tbe egg 
thus loses its radial symmetry and becomes two-sided. It is important to notice that no pro<lncts 
of the segmentation nucleus are left in the interior of the yolk. The superficial pyramidal 
structure is lost ^ the primitive blastoderm is established, and there n<4w takes place a general 
migration of nuclei from ftie surface to the yolk within, but principally, as would be expected, 
from that part of tbe 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 
cellFfrom the surface, prior to invagination. This is also true of Pontonia domestica, and it is quite 
probable that the majoiity 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 instead of 
multiplying by regular binary division, multiply indirectly, and give rise to numerous nuclei, 
many of which degenerate, before the blastoderm is formed. 

THS 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 yolk frag- 
ments, and probably digests them by an intracellular process, after the manner of feeding amoBbaB. 
The thickening in front of and surrounding the pit, which is now obscured, is the rudiment of the 
abdomen. Anteriorly the " procephalic lol)es ^ or more properly the optic disks make their api)ear- 
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 prim- 
itive blastoderm. The majority, however, pass forward and upward in divergent lines from the 
sides of the abdominal plate, and eventu£dly large numbers of these wandering cells settle down 
over the dorsal surface of the embryo. 



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336 MEMOIRS OF THE NATIONAL ACADEMY OF S0IBK0E8. 

PRODUCTS OP CELL DBGENBRATION. 

At the beginfiiiig of the egg-nauplius period^ when nameroiis 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 nniformly, 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 socalle<l '' secondary mesoderm cells," originate and 
what is their function! A^ 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^he fully developed egg-nauplius, where there 
is a large accumulation of them around the oesophagus and at the bases of the rudimentary 
appendages. After this stage they geuerally disappear from these regions. Somewhat later, 
however, when there is a well developed nervous system and six pairs of post-naupliar i^pen- 
dages, a patch of ectoderm cells on the surface of the e^gg 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, th^t is, ^ey possess a deeply staining nucleus aud 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 Beichenbach's views on the function of secondary mesoderm cells of Astacns 
are probably erroneous. According to this naturalist they arise from the nuclei of the endoderm 
cells, forming the ventral waU of the primitive stomach, and are converted into mesoderm. 

THE GERMINAL LAYER^. 

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 ^gg 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 eggnauplius 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 ETE. 

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 right angles to the surface. A disc 
of cells is thus formed which gives rise chiefly to the eye and its ganglia. The cord of cells uniting 
the two optic discs 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 ^gg given at the end. 



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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 337 

<K>NOI)A0TYLUS GHIBAaBA* 

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 Squillae 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 Qeaufort, North Carolina; but, except for a few scattered and fragmentary notes in 
the various descriptive papers, this is the whole of our knowledge of the order. During the sea- 
sons of 1886 and 1887 I was so fortunate as to find in the Bahama Islands OonocUictyltis 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 it is the most cosmopolitan of the 
Macroma abounding on the shores ^d islands of all tropical and subtropical seas. 

I also obtained its e£:gs 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, larvae 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 larvae 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 theii" constant and rapid oiovements, 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 
aerated by the currents produced by the abdominal feet of their parents. The eggs quickly 
perish when deprived of this constant current, and as it is very difficult to obtain them at all, I know 
of no Stomatopod which has ever been reared from an egg under observation. The older larvae 
are hardy and are easily reared, but they are seldom 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 Stomatop(»da, I have 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 larvae 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 larvae 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 larvae 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 J r\r\r^]o 

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338 MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES. 

collectors the successive stages in the history of a single species. Like the adalts, they are widely 
distribated) 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 larvae of several widely-separated species of adnlts in all stages of growth as well as the larv» 
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 diflQculties, and the earlier wrjteris were content to rest after 
the bestowal of generic and specific names upon the larvae. As I found after the Challenger collec- 
tion was placed in my hands that it was very rich in larv®, 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 ventUAcd to describe the 
general characteristics of the larva of the genus Oonodactylns (p. 113), and in PI. xu. Fig. 5, of 
that report I figured a larva which I ventured to call the larva of Gonodactylus. A comparison of 
that figure with PI. xv, Pig. 11 of this memoir will show that this determination was correct, for 
the larva of Oonodactylua chiragra which is here described is so much like the one figured in the 
OhdUenger report that they belong, in all probability, to the same species. 



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CHAPTER II. 
THE LIFE HISTOBY OF STEHOPUS. 



By Peanois H, Hebbigk. 



This paper is the result of observations made at Beaufort, North Oarolina, in 1881 and 1883, 
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 larvse at Beaufort, and it is very probable 
that they represent a part of the life history of Sienapus hispidus. Plates rx and x, illustrating 
two important stages of these very interesting larvae, are contributed by Professor Brooks, and 
the descriptions of these stages are based entirely upon his observations. 

While the material gathered in a sojourn of a few 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 Atlantic (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 
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). 

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 PensBUS 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 sufficiently well for the purpose in hand, although it rendered the eggs 
more resistant than is desirable. 

I.— THE NATUBAL HISTORY OF STBNOPUS. 

The Bahaman Stenopus (PI. v) measures from 1^ to If inches in length.- All the appendages 
are long and generally quite slender and delicate, especially the antennae, which give to this form 
a very characteristic appearance in the sea. These are snow-white. They are carrieil widespread 
and arch outwards in graceful curves. The flagella of the second or outer antennae are two and a 
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 antennsd is carried upward, and their inner branch is 
directed forward. 

The boily 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 
and bases of the antennae, and in some cases it extends behind the rostrum as far as the mandib- 

339 



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340 MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 

ular or '' cervical ^ groove. The second is nearly confined to the broad tergal sarface 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 th^ 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 
differeut'sexes, but it is most remarkal^le 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 Baraka, 
one of the Paumotu Islands, and at Balabac Passage, north of Borneo. Both oi 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 Oanodactyltts 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 f To this question we can not at present 
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 red. 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 frawn." 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 clinging 
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 Jnne, but the breeding 
season, as inferred from the capture of locomotor larvae, 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 larvae 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. 

* Besides Milne-Edwards figure (4), evidently made from a specimen in which the natural colors had been removed 
by alcohol. (See remarks, etc., under Section iv.) 

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 341 

Aftei: a moalt the colors are, as is asual, very bright, and the moulted skin, as it stands intact 
supported by the auteunse, may easily be mistaken for the living animal. These prawns make no 
sounds and appear to be very timid. The surfape 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 att^icked from the rear. Their long sensitive antennae or 
"feelers" and well-developed eyes doubtless warn them of approaching enemies, which, by their 
rapid angular movements, they ipay easily escape. The extraordinary development of the eyes in 
the older larvae (PI. ii) is remarkable. 

The geographical distribution of Stenopus hispidus is very interesting.* H. Milne- Ed wards, 
in his "Histoire naturelle desGrustac^s" (3), gives the habitat of Stenopus hispidtis (Latreille) as 
the "Indian Ocean,'' following Olivier (1) and the older writers. In the "R^gne Animal" of 
Cuvier, third edition, " Les Crustac^s," 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 1838-'42, 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, id a collection of Cuban Crustacea made 
by Dr. J. Oundlach, 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). W^e 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 therefore 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 another 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 Oonoda>ctylus 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 

II. SEGMENTATION AND EARLY PHASES OP THE EGO. 

The prawn, which hatched her zoea 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 6 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 we 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. vi. 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 coosideriog the Bahaman form identical with the Hispidns of Olivier, Latreille, Milne-Edwards, 
Adams, Dana, and others are given on page 351. 



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342 MEMOmS OF THE NATIONAL ACADEMY OF SCIENCES. 

another egg of the same phase neither cell is qaite at the surface, so that the example given in 
Fig. 1 may be taken to illastrate a tendency, not a rjfle.* The yolk (Fig. 1, T. C.) consists here, 
as in sabseqaent stages, of homogeneous and tolorably uniform green corpuscles. No vacuolar 
cavities are to be seen. 

Second stage. — Four and one-half hours 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 sections, 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. — After three hours and twenty -five minutes have passed the third phase is reached 
and we have eight cells, around which 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. 
yi, 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, Pal®- 
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 neater 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 migi*ation to 
the interior, as there is in Alpheus, before invagination. 



* It now seems probable to me that this superficial cell represents the male and the central cell the female pro- 
nncleas. 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. 



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MBMOmS OF THE NATIONAL ACADEMY OF aOIENOES. 



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 (^ggj which loses its radial symmetry in consequence. 
There is thus formed the embryonic area or first trace of the embryo proper. 

Eighth or invagination stage. — Three and a half hours later a portion of the blastoderm in ihe eni- 
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 here segmented into large, irregular 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 discs, and an accumulation of large granular cells in the abdominal area. These latter^un* 
doubtedly represent some of the primitive mesoderm and eudoderm. 

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 strictJy 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 4nay be seen in embryos from the same 
female.* 

Time of hatching Jane 4, a. m., early. TemperahiTe 8(P F. Diameter of egg ^ inch. ^ 



stage. 


Age of egg. 


state of development. 


1 
2 
3 
4 
5 
6 
7 
8 
9 
10 


6hr8 


2ceUs. 
4 cells. 

16 blastomeres. 

32 blastomeres. 

128-256 blastomeres. 

First trace of embryo. 

Inyagination stage. 

Pit obscDred. 

Optic discs and abdominal plate formed. 


ll^hrs 


14 hrs. 55 min 

lehrs 


19 hrs 


28 hrs. 45 min 

32ihr8 


35ihr8 


38^ hre 


52 hrs 





We thus have in Stenopus a type of the so-called " centrolecythaF segmentation, exactly 
comparable to that of Penaens, 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, Homarua amerioanu8f in which I have made^ a very complete stady of 
the segmentation process. In a batch of 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. 



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344 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



A. Protozoea or first larva (length =4""). — Stenopus leaves the egg as a protozoea. which may 
be compared ta one of the early larvte of Peuseas or Sergeates, but it is anlike 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 antennae and the long rostrum which 
was bent under its body.* 

The figure on PL xi exhibits some of the grotesqueness of this larva. This drawing was made 
from au animal which had just wiggled out of its egg shell and was uncoiling its appendages. 
The huge antennee are partially unfolded, while the rostrum B., is scarcely visible. Drawings of 
parts of this immature protozoea are seen in PL vii, 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 structjures grow rapidly ; hairs or setae are developed on 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 protozoea (PL vii, Fig. 11) is 4"°* long, the rostrum alone being IJ"". 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-fin. It swims chiefly by aid of its largely developed antennas, 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 viii,- 
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 xi. Fig. 25, Md.) and by its forked telson-plate, 
adapted for swimming. The forked locomotor tail-fin and large hairy antennsB mark the protozoea 
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 
antennaB. 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 up|)er surface of the 
second segment is also prolonged posteriorly into a median spine." The tail-fin at the time of hatch- 
ing is sharply forked (Fig. 13) and is furnished with 6 pairs of rudimentary setae, of which the 
median pair is the shortest, besidt s 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. 

The eyes are sessile. The inner or first antennae (Fig. 25, AI) 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 spiings from the distal end of the penultimate joint on its inner side. 
The outer antennae are biraraous. 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 setae, 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 vii. 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 lobe is provided with hairs, 
excepting the outermost which corresponds, in part certainly, to the scaphognathite. 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 



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MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 345 

Figs. 14 and 16, which represent the first and third maxillipeds 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®, lih^re is one pair of thoracic limbs consisting of a stont locomotive exopodite, 
similar to that of the second and third maxillipeds juHt described, and of a very short, indistinctly 
segmented endopodite. The latter is armed with two terminal and three lateral plumose hairs on 
the inner side. 

B. First zoea or second larva (length, a=5™"). — Five or six hours after hatching the pro- 
tozoea 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 gieatly developed, and extends to nearly 
the end of the third somite. The sixth somite, which carries the zoeal 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 rudimentary spurs seen in Fig. 11 being wanting. The eyes, which have acquired 
short stalks, protrude slightly. 

The antennse are shorter and are now no longer so important as organs of locomotion. The 
terminal joint of the inner antenna is reduced, but otherwise this appendage is but little changed. 
The outer antenna ends in a stont 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 maxillae (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. ITie second maxillae (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, all of 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 cxopodile 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 firs^and second maxillipeds and the first pair of thoracic legs. The inner branch 
of the latter is considerably developed, and nearly equals the exixxlite 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 protozoc?a (Fig. 25), is finally absorbed. It was probably owing to this and to the fact that 
I gave the larvae 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 zoea with the adult, we have to 
rely upon larvae collected at the surface of the ocean. 

O. Mysw or Schizopod stage. — It is evident that- the zoea of the stage B passes into a mysis- 
like form through the intervention of one or more moults, and we have two larvae already noticed 
belonging to the close of this perioil. 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 appendaf^e correspond to the coxopodite. 



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346 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 

1883. In the Beaufort specimen (PL ix) all the segments and ap]>endage8 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 fh 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 protozoea, 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 antennse are biramons; 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 nropods well developed. 

D. Mysis stage. — The larva of stage C moulted into a form (PI. x) redembling the last, with the 
addition of several important features. The inner antennse 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 scale is as long as the antennular peduncle. The fiagellum of the antennae now 
appears as a slender filament, nearly twice the length of the scale. Possibly it is formed, as in 
Penceus, from a bud-like remnant of the inner ramus of this appendage in the protozoea. The 
third pair of maxillipeds and first to fourth pairs of thoracic legs are as in the previbus stage, with 
conspicuous exopodites fringed with setsB. 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 i>enultimate 
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. 

E. 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 
antennsB are biramous. The outer flagellum of the first or inner pair of antennae is the longest (PL 
XI, Fig. 26), and it bears four or five bunches, containing in all about a dozen sensory filaments. 
The inner branch is a bud. The second antennas extend as far forward as the joint of the first 
pair, where the inner flagellum is given oflf. The flagellum of the second pair is wound into a 
short spiral coil. 

The exopodites of the second pair of maxillipeds are rudimentary (PL xi, Fig. 31). The third 
maxillipeds are now the stoutest appendages, and equal in length the third pair of thoracic limbs. 
The first and second thoracic legs are slender; the third pair is the longest and the terminal seg- 
ment is bifid; the fourth is a short two-jointed rudiment; the fifth, corresponding to the huge 
oar-like appendage of stage 0, is reduced to a bud. It thus appears thaty as in the Sergestidsy the 
last two pairs of icalkin<f legs are shed after the mysis period, to be reconstructed again in the masti- 
gopus stage. 

•All the abdominal appendages are functional. (PL xi, Fig. 27.) The last segment of the abdo- 
men is nearly equal in length to the three preceding. It is laterally compressed, and more nearly . 
resembles the adult form. In the act of swimming this larva carries the abdomen bent at nearly 
a right 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 antennae 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 OP THE NATIONAL ACADEMY OP SCIENCES. 347 

F. Mastigopna stage, — After it had been kept thre-e days this larva passed through a nioalt, 
by which only slight changes were introduced. The fourth pair of walking legs is now distinctly 
jointed, the fifth remaining as a bud. The flagellum (endopodite) of the second pair of antennae 
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 ecdysis. 
Figs. 26, 27, 30, and 31 are from this stage. 

G. Mastigopus stage [PI. xi. Figs. 28, 29, 32-34, PI. xii], (Length = 9°^").— An older larva, 
caught in the net on May 7, is shown on PI. xn. The most striking features of this form are the 
long trailing antennoe (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 app<»arance. * 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 p^issing to the adult stage the 
eye-stalks are much reduced. The outer antennsB have a short peduncle; along scale, armed 
with stiff hairs on the inner margin, and a long flagellum, all very much as in the adult prawn. 
(PL XII, and PI. xm. Figs. 40, 41.) The first pair of antennse are much less like the adult form. (PL 
xn and Fig. 40). The stalk 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 eud 
of the carapace. The rostrum is short and stout, bent upward, and does not reach beyond a line 
passing through the vesicnla auditoria. The frontof the carapace bears also a short dentiform 
process on each side below the rostrum. These are the only indications of the future 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 longest 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 maxillse 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 xi and also in Fig. 31 (St. F.). 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 xi, Mxp. in.) The terminal joint l>ears 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. xiii. Fig. 47.) The terminal joint of the sec- 
ond thoracic limb is shown in Fig. 32; th^ ba«al extremity of the third, the fourth, and £ftli are 
given in Fig. 34. The second and third pair are chelate; the fourth is rudimentary; the fifth is 
still a bud. The abdominal appendages, excepting the sixth pair described above, are all unira- 
mous. (Fig. 27.) 

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348 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

This larva is colorless, excepting large spots of reddish pigment, distributed mnch 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 G 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 Penaeus, 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 cull 
attention to the apparent similarity of the second larva of Stenopus (PI. vin. Pig. 17) to the zoea 
of Oallianassa gtibterranea^ figured by Claus.* The length in each case is 5"»"». He says, p. 54: 

Die jnngen CaMiaDaaaa larven besitzen beim Verlaasen der Eihiillen eine ansebnliche Groese, sind •ehrlang- 
gestreckt nnd tragen drei spaltUstige FUsspaare, vod denen sich das Vordere scbon we«entlicb der Formgeataltang 
de8 Hptiteren Maxillarfasses nabert. Der langc BtirDscbnaU*!, Howie die Bestacbelung des AlMlomeus, dessen zweites 
Segment mit einem besonders langen Rtickendom bewaflfnet int errin«*rn an die oben boHchriebene larve, 

which applies perfectly to the Stenopus zoea, except that the latter has the first thoracic segment 
with its appendages, while, according to Claus, the first zoea of Oallianassa has not, although his - 
figure is not clear on this point. The rostrum, eyes, antenusB, second maxillae, 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 tin 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, 
schlauchformigeu Anlagen sammtlicher Thoracalfiisse unter dem Integument bemarkbar sind." 

Among the Prawns, Penseus 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. 

rV. THE ADULT. 

Stenopus (Latreille). 

Cancer (Herbst). 
Pakemon (Olivier). 

Sterwpus (Latreille) L^ach, Deismarest, Boux, Milne, Edwards, Adams, Dana, etc. 
Diagnosis of Stenopus hispidus (LatreiUe).— Body nearly cylindrical. Carapace "^th prominent rostnun and 
distinct transverse groove. Outer antennee with long, bristle-bordered scale bent under the inner antennas 
toward the middle line. Second maxillipeds with epipodite and long ezopodite. Third maxillipeds very 
long and appendicular, with a rudimentary ezopodite 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, aU the others biramous. 

Special description. — Length, 37-44""" (IJ-lf inches). There is 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. AntennsB snow 
white. For further particulars under this heading, see PI. v, and Sec. i. 

The carapace (Fig. 37) presents a marked transverse fossa. It is covered with short dentiform 
spines, largest on the front. The ro.^truni is elevated, extending hardly beyond the basil joint of 
the inner/tntennse. It ends in a sb*arp 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 : " UDtersuchungen znr Erforschung der geaealoj^ischen Grundlage des Crastaceen-Sy sterns.'^ Wien, 
1876. Taf. vui, Fig. 1 ; also Figs. 3-7. 



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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 349 

rostram also bears ou 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 antennsB. 

The epidermic spines, which are' characteristic of the Hispidns, 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 a|)pendages generally. The first, second, fourth, and fifth pairs of thoracic 
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 ou either side by a longitudinal elevated ridge, bearing spines; it 
hardly surpasses the uropodal lamella. The eyes project at right angles to the long axis of the 
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 Ungulate appendage, which is supported by a thin, median, and vertical plate. The 
inner antennsB (Fig. 40) bear very long flagella, the disposition of which has already been noticed 
(Sec. I). Tiie 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 antennse (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 laige 
palpi, and have blunt interlocking teeth ; a transverse furrow divides the cutting surfaces of each. 
The first pair of maxillsB (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 maxillae (Fig. 42) are furnished with an elongated plate, the "bailer'' or 
scaphognathite, which is fringed with hairs, an inner lobulated portion (basipodite and coxopo- 
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 long 
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 denticulated ; the distal extremities of the segments, as of the 
ischiopodite, produced into a sharp 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 chelae," 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. 



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350 



MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 



The fourth pair of pereiopocls (Fig. 48) end in short bifid daotjles, the terniiDal claw bearing 
a shorter proximal one below. The propodas is snperficiall^' segmented into from five to seven 
rings, which vary in size. The right propodas 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 pro^iodus 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 proi>odus and carpus are divided diflter within the above limits in different 
individuals of either sex and on the right and left sides of the same iridividual. The pleoi>ods are 
all biramous, excepting the first pair, in which the endoi>odite is suppressed as shown in Fig. 44. 
This i)air 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 setie. 

Measurements (in millimeters), 

[Locality: Naman, New Providenoe, Bahama Inlandii.] 



Sex 

Length from tip of rostmm to end of telaon 

Length of carapax, including rostrnm 

Greatest breadth, inclading spines 

Greatest depth, including spines 

Length of rostrnm 

Distance between transverse fnrrow and tip of rostrum 

Length of first abdominal tergum 

Length of second abdominal tergnm 

Length of third abdominal tergum 

Length of fourth abdominal tergnm 

Length of fifth abdominal tergnm 

Length of sixth abdominal tergum 

Length of telson 

Gratest breadth of telson 

Length of eye-stalk 

Greatest d i ame ter of eye 

Breadth between eyes 

Stalk of inner antennae 

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 antennw 

Greatest breadth of the same 

Length of stalk of outer antennie 

Breadth of stalk of outer antennae 

Length ot flagellum of outer antennse 

Breadth of flagellum of same at inner end 

Length of third maxilliped 

Length of terminal joint of the same 

Length of basal joint of the same 

Breadth of basal joint of the same 

Length of exopodite of the same 

Length of first pereiopod 

Length of propodns of same 

Breadth of propodns of same 

Length of dactyle of same 

Length of carpus of same 

Length of second pereiopod 

Length of propodns of same 

Length of dactyle of same 

Breadth of propodns of same 

Length of carpus of same 

Length of meros of same 

Length of left third pereiopod , 

Length of chela 

Greatest breadth of same with spines 

Greatest depth of same with spines 

Length of dactyle 

Wid th over tooth of dactyle 

Lrn;;th of carpus of samo 

Greatest breadth of carpus without spines 

Greatest breadth of carpus with spines 

Length of nieros of same 

Length of right third pereiopod 



37 
14.5 

8 

7.5 

4.5 

9 

1 

2.5 

5 

3 

2.8 

4.5 

8 

3 

3 

2 

6.5 
45 

1 
73 
75 

9 

1.8 

1.5 

1.5 
92 

0.4 
18.5 

2.5 

5 

1 

5 
20 

5 

1 

2 

6 
27 

6.5 

3 

1.5 

9 

7 
48 
19 

5 

3 

7 

2.1 

9.5 

3 

4 

n 

46 



9 


(/ 


9 
44 


40 


43 
16 


44 


10 








10 
















10 








1.5 








3 








5.5 








.3 








3 








5.5 








9 








4 
















2 








7 


























86 
98 













































119 




























































5 








1 








2 








8 
















7 








3 




...... 




2 








11 








8 








53 








22 








6 








4 








9 








2.5 








12 








3 








4 








12 








51 , 

















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MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 
iteaavrements (in millimeters) — Continued. 



351 



Sex. 



LeDgth of chela of the same 

Greatest hreadth of same with spines 

Greatest depth of same without spines 

Length of dactyle of same 

Width over tooth of dactyle . . . ; 

Length of carpns of right third pereiopod .. 

Greatest hreadth of same with spines 

Greatest hreadth of same without spines .... 

Length of meros of same ...i 

Length of fourth pereiopod o, 

Length of dactyle of same ., 

Length of propodus of same , 

Numher of rings in propodus , 

Length of carpus of same 

Number of rings in carpus 

Length of meros of same ^ . ^ 

Greatest breadth of meros 

Length of fifth pereiopod - 

Length of propodus of same 

Number of rings in propodus 

Length of carpus of same 

Number of rings in carpus 

Length of meros of same 

Length of first pleopod 

Length of third pleopod 

Length of inner lamella of same 

Breadth of inner lamella of same 

Length of outer lamella of same 

Length of inner lamella of uropod 

Length of outer lamella of uropod 

Greatest breadth of outer lamdla of uroi>od 



18 

5 

4 

7 

2 

9 

4 

3 
12 
36 

1.5 

5 

5 
14 
12 
10 

L4 
30 

5* 

6 
15 
13 

9.5 

3 



19 
5 
3 



11 
4 
3 

12. 



1. 

5 

5 

18 

12 

11 



6 

6 
16 
12 
11 

7 

9 

6 

2 

6 

8 

9 

3.5 



Eemabks. — ^The earliest figure of Stenopus hispidus with which I am acqaainted is that of 
Olivier, published in 1811 under the name of Palwnwn hispidus (1, PI. 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, c'^toit la droite qui 
manquoit et paroissoit repousser de m^me." The next drawing appears in Milne Edwards's Atlas 
(3, PI. 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 
Guvier's Le E^gne Animal (4, PI. 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. xn. Fig. 6), already noticed, and his brief description agree essentially with the 
Nassau form. The antennae 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 Penseus, 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 ruffled.'' 
The drawing by Dana (6, PI. 40, Fig. 8) represents the antennsB of this animal for the first time 
in a natural x>osition. 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 2J 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 sleudemess 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 



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352 MEMOIRS OP THE NATIONAL ACADEMY OP 80IEN0E8. 

in their nataral positions, and in their troe relative proi>ortion8. 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 individual 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 si>ecies 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 gezeichuet, in Spiritus blass orange and 
mehr hartschHIig; 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. 

So far then as we can judge from the figures and meager descriptions in our |>osses8iou, the 
Asiatic Steuopus 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 2^ and 3 inches by Adams and Dana resi)ectively. None of the Nassau 
specimens which I have measured were more than If 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 hiapidua (Latr.): 

DistribatioD : (a) Indian Ocean, Borneo, and Philippiqe« (Adams). 

(b) Paamotu Islands and Balabao Passage, north of Borneo (Dana). 

(c) Amboyna, Cuba (Von Martens). 

(d) Abaco and New Providence, Bahama Islands. 

(o) *<Red Sea, Indian Ocean, Indian Archipelago, New Guinea'' (de Man). 

(2) Stenopus apinosus (Bisso) : 

Mediterranean (Heller), teste Von Martens and de Man. 

(3) Stenopas anaiferus {Dana): 

Fiji Islands. 

(4) Stenopus aemilcema ( Von Martens) : 

(One specimen in the Berlin Zoological Museum, purporting to have come from the West Indies. Length 12™™. 
Von Martens.) 

(5) Stenopus tenuirostria (de Man) : 

Amboyna : Length 24™™. (More closely allied to Stenopus spinosus of the Mediteranean than to Stenopus 
hispidus, and is the representatiye of the former in the Indian Ocean ; de Man.) 

STENOPUS UTERATURE. • 

(1) Olivier: EncyclopMie M6thodiqne, Hist. Nat. Insectes, t. yiii, p. 666, 1811. 

(2) Latrmlle: Encyclopedic M^thodique, Hist. Nat. Crustaces, Arachnidses, et Insectes, t. 10, Paris, 1882. 

(3) Milne Edwarda, H. : Hist. Nat. des Crustaces, t. 2, p. 406, ia37. 

(4) Milne Edioardsy H.: Le R^gne Animal, Cnvier; Les Crustaces, with Atlas, by Milne Edwards, p. 137. 

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

(6) Dana, J. D. : U. S. Exploring Exped. U. 8. N., 1838-1842, vol. xiii, pt. 1, Crustacea, p. 607. 

(7) Mariena, E, v. ; Uebei Cubanische Crustaceeu ; nach den Sammlungen Dr. J. Gundlach. Archiv. f. Naturgesch., 
38. Jahrg., Bd. 2, 1872, p. 143. 

(8) Heller: Crustaceen des sUdlichen Enropa, 8. 299. (I have seen only references to this paper.) 

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



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CHAPTER III. 
THE HABITS AHD METAMOSPHOSIS OF 00V0BACTTLU8 CHIRAOBA. 



By W. K. Bbooks. 



(With PI. I, III, XIV, and xv.) 

The Steuotube and Habits op 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, Medit^ranean, Gape St 
Eoque, Samboauga, 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 irom it by only very minute differences. There is a well-marked 
chiragra-like group of species all so close to each other that their divergence from each other mnst 
have been comparatively recent, and in view of this fact it seems remarkable that one of these 
species should so x>«rsistent!y 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 tbe base ; rostrum consisting of a transverse proximal portion 
more than twice as wide as long, with subacute anterolateral 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 ellge of the 
carapace, which is nearly transverse with ronnded postero-lateral angles; the transverse cervical 
suture is faintly marked, distant from the anterior margin about two-thirds of the length of the 
carapace; second thoracic somite, 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 
carina, 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 carinaB on the first five abdominal somites, and 
no median dorsal carina on the sixth,* which carries three pairs of swollen convex lateral carinae, 
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 carin» project beyond 
the posterior edge of the somite and lie in the same transverse plane. 



S. Mis. 94 ^23 

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554 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

The fifth abdominal somite is somewhat longer than those in front of it, and abont twice as 
long as the sixth. The telson sometimes presents slight variations, but most of its characteristics 
are well marked, so that there is unnally 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 carinse, 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 ; e:fternal to 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 halfway 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 otliers 
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 itiner, 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 
cornesB, and the first and second antennae are about equal in length, and more than half of tbe 
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 spots or markings of any sort, as shown in PI. iii; 
while the other form, which is copied in PL 1, Fig. 2, is more transparent and is delicately mottled 
over the entire dorsal surface in an intricate but constant 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 reticulum. 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 of 
the uniform green color, I tbund 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 I 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 rock or 
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 tbe 
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 anijual 
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 fiask-shaped cave (PI. iii), with smooth, even walls and regufar 
curvature, and large enough for the animal to coil up or turn around inside it. Most of the burrows 
are horizontal, but many s^e vertical with the opening below, and a few are vertical with the 
opening above. , ^.^.^.^^^ ^^ L^OOgk 



MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 355 

The aDimals asnally rest coiled up, with the eyes and antenuse directed oatwards, jast 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 I have 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 tbat they must be constantly exercised by the animals when at 
home. 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, ahhough they may be on opposite sides of the aquarium, and* the constant motion 
of their eye stalks shows how intently each moveipent 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 oat 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 tbe 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 aeration 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 Oonodactylua chiragra. As the pelagic larvsB 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 larvae 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 larvae by actually rearing it from the 
egg is a most noteworthy and important occsision. 

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- x 
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 animal. 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 

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356 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

the GoDodactjli scattering ia all directioDs, 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. iii, 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 armful, 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 instinct 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 Solent shock, it fiees from its cave to escai>e 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 opi)ortunity 
to observe except this species, and the chief use of the burrow of iSquilla fmpusa is for refuge in 
danger, while Lysiosquilla excavatrix darts down its burrow at the least alarm and can not be 
driven out even when the sand has been dug up on all sides of it 

The Metamorphosis of Gonodagtylus chibagba. 

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 Oonodactylus chiragra 
rendered it an easy matter to obtain this history for that si>ecies. 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 diflference from other Macroura as regards the egg 
embryology, this subject was not studie4l. 

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 larvse are very 
scanty. In 1882 Faxeu publisheil aq account (Selections from Embryological Monographs com- 
piled by Alexander Agassiz, Walter Faxon, and E. L. Mark, 1 Crustacea, Cambridge, 1882, Bull. 
Mus. Comp. Zool., Vol. ix. No. 1, PI. viii, Figs. 2 and 3) of observations made three years before 
upon a young Squilla einpusa 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 larvae 
which I had studied while they were alive, and which was sufficiently complete to warrant the 
statement that they were the young of Squilla 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 
Besults of the Voyage of H. M. S. Challenger during the years 1873-'7G, xvi, part xlv, 1880) I 
have given an account of the metamorphosis of Lysiosquilla excavatrix which I had reared at 
Beaufort, 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 larvae 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 affini- 
ties of theoldest larvae, by Clans (Die Metamorphosen der Squilliden, AbhandL d. Jc, Gesellsch, d. 
TFm., Oottingeny Bd. xvi, pp. 1-55, Pis. i-viii, 1871) and 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 larvae, and gave a scheme or outline of 
the probable metamorphosis of each genus of adult Stomatopods. . i OOCtIp 



MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 357 

Stotnatopod larvse or Ef IchtliidaB, as tbej were named before their larval nature was suspected, 
have been divided into four genera, Erichtkoidiim^ ErichthuSj 8quillerichthtiSj and Alima. Of these 
four the first, Urichthoidinaj is simply a younger stage in the life of the UrichthuSj and the third,- 
SquUlerichthuSy a fully-grown larva of the Urichthus type, so that the genera become reduced to 
two, Erichthus and Alima. Of these two genera, one, Alima^ is much more sharply defined than 
the other, ErichtlittSj 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 
adult genus to which each corresponds. I have shown that there are many reasons for believing 
that all Alimi are Squilla larvj©; AlimeriehthuSj the larvae of Chloridella; Erichthalima^ the larvae 
of Coronida; LysierichthttSj the larvae of LysiosquilUij and Pseuderichthus, the larvae of Pseudo- 
gquilla. The remaining larval type may be distinguished from the Lysierichthus by the shallow- 
ness of ils 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 larvae 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. For this larval type, which was represented in the Challenger collec- 
tion by many specimens, I proposed the name OonerichthuSy giving, at the same time, many 
reasons for regarding it as the larva of the genus Gonodactylus. Several of these larvae were 
selected and shown in PI. xii. Fig. 5, PL xiii, Fig. 9, and PI. xv. Figs. 1 and 5, of my report; and 
I pointed out that in all of these larvae, 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, another internal to the base of the intermediate, and a third midway between this and the 
submedian. 

In PI. XV, 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 
h>ng 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 ot* else to a new 
~genus. It is not probable that a larval type which is so common pertains to an unknown adult 
genus. The larvae are not Protosquilke^ as this genus has the telson fused with the sixth abdom- 
inal somite, while it is free in the older larvae; nor are thej Pseudosquillce^ 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 larvae indicate that they are the young of di)ecies 
in this genus. 

Led by these considerations I did not hesitate to speak of these larvae, 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 larvae which I reared from the eggs of Oonodactylus 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 PL xiv. 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 sessUe. ^.^.^.^^^ ^^ L^OOgk 



358 MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES. 

The larva, immediately after hatching, ia shown in side view in Phxiv, Fig: 3; in ventral view 
in PI. XY, 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 emargiuated, 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 antenuule 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, idthough it is of little use in locomotion. The large eyes are subspherical, 
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 maxillse 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 maxlllipeds, corresponding to the third maxillipeds and first and second ambulatory 
limbs of decapods, are rudimentary, and the three following api>endages are absent, although all 
the corresponding somites are indicated as well as their ganglia. The abdomen is about 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 car- 
ries seven or eight pairs of minute movable spines. The newly hatched larvie swim actively about 
by means of their abdominal feet, not by fiexiiig 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 larvse, nearly 
a thousand in all, soon settled down upon them, covering them completely, and at once began 
tearing them olf and eating them. When washed away from tliem by means of a jet of water they 
swam about the aquarium for a short time, but soon settled down ui>on the eggs again. As these 
eggs are not very abundant they can hardly be the only food of the young larvae, although I could 
find nothing else that they would touch, and they refused the eggs of all 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 sidei view in PI. 
xrv. 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 antennae 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 api>earance 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 PI. xrv, Fig. 5. The rostrum is now greatly 
elongated and reaches to the tips of the antennules. Small anterolateral spines have made their 
appearance, as well 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 PI. 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 



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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 359 

sixth abdomiDal somite has separated from the telsoD, bat its appendages are not yet developed. 
The scale 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 adnlt form, while at the earlier stage they closely resembled the chelsB 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 Erichthns of Oonodactylus chiragra presents the characteristics of that larval type 
for which I have proposed the provisioual name Gonerichthns; 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. xiv. 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 Ohallenger report 
in PI. XV, Figs. 1, 5, 6, and 11, it resembles these larvae in the following features as well as in 
many minor points: The rostrum is long and reaches beyond the tips of the antennnles, and it has 
four or five median teeth on its ventral surface. The anterolateral angles of the cairapace 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 a little 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 larvae (Figs. 3, 
4, and 5 of PI. xiv), has disappeared, although it persists until a much later stage in the larvae 
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 spiuule, and the fourth, which, at the stage shown in Fig. 6, PI. xiv, 
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 PI. 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 PI. 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 larvae 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 



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360 MBMOIES OF THE NATIONAL ACADEMY OP SCIENCES. 

the three pairs of fVee thoracic legs, and the oropods are represented by buds. An umber of moults 
and probably au iuterval of many weeks intervenes between this stage and the one shown in PL xy, 
Fig, 11 of the Challenger report 

The life history of this species of GonodactylnSy in the Bahama Islands at least, is thus seen 
to be extremely simple. It hatches as an Erichthns and remains an Erichthns 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 Oonodactylus hatches from, the egg in the Erich thoidlna stage and subsequently 
changes into an Enchthus, is an error, at least so far as Oonodactylus chiragra is coucerued, 
although it is possible, in view of the great variation which we have observed in a single species 
of Alpheus*, that in other regioos, where the adults have different habits, the larva may batch in a 
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 Oonodactylus may have 
an Erichthoidina stage. 

The Challenger collection contains a bottle of very minute and young larvae in the Erichthoi- 
dina stage, and one of these is shown in Fig. 3 of PL xii of my report. Comparison between this 
and the newly hatched Erichthns of our species, PL xiv, Fig. 3, will show many points of resem- 
blance, and future research may possibly prove that it is the larva of Oonodactylus, although the 
statement that all €k>nodactyli hatch as ErichthoidinsB is an error. 



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CHAPTER IV. 
THE METAMOEPHOSIS OP ALPHEUa 



By W. K. Brook and F. H. E^bbioe. 



(With Pis. I, II, IV, XVI to XXIV. ) 

Section I.— The Metamorphosis op Alpheus minor prom Beaufort, North Carolina. 

This small species isfoaod in abundance at Beaafort, North Carolina, and in the Bahama Islands, 
and it is no donbt widely distributed along our southern coast. At Beaufort it is 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 Alphetis normaniy pass through the same metamorphosis, the 
'life history of Alphetcs minor may be regarded at the primitive or ancestral life history of the 
genus, which originallj^ 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 
beformthe 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 tfps of the exopodites of the three pairs of maxillipeds, 
and the plumose hairs on the antennules and antennsB are not fully extended until after the change. 

The second larval stage is shown in PI. xvi. Fig. 2, and in PI. xvii. Fig. 2, and various organs of 
the larva during the first stage are shown in PI. xvi. Figs. 4, 6, 7, and 8, and PI. xviii, Fig.. 4. In 
PI. 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 PI. xviii, the first maxilliped. As shown in PI. xvn. 
Fig. 2, and in PI. xvi, Fig. 2, the locomotor organs of the larva during the first and second stage 
are the plumose exoi>odites of the antennsB 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 b\x segments, there 
being at this time no joint between the telson and the sixth abdominal segment. . During the first 

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362 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

Btage there are no traces of any abdominal appendages, bnt in the second stage, the outlines of 
the sixth pair aro faintly visible under the cuticle of the U'lson, 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 PI. XYi, Fig. 2, the antennule consists of a stout shaft comi)osed 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 fiabellum 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 anunlated, as shown in PI. xtt. Fig* 
4. At this stage it is divided into a basal portion and five movable joints, about equal in total 
length to the basal i>ortion. After the first molt the annulations become less distinct, although 
the << scale " is still cylindrical, as shown in PL XYi, 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 PI. 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 endoi)odite carries 
two terminal hairs, and the fiat exopodite is fringed by seven. I could not determine whether 
these hairs are plumose or not. The three pairs of max;llipe<l8 are functional and they present 
features which are characteristic of the genus Alpheus (see PI. xvi. Fig. 2). Bach has a large, 
flattened, polygonal, basal joint, which carries upon its inner edge a few short, sharp teeth, and* 
ui>on its outer edge a long, flat exopodite, 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. xviii, Fig. 4, is telescoped l>efore 
the first moult, but immediately afterwards becomes lengthened, as shown in PI. xvi, Fig. 2, until 
it reaches forward beyond the tips of the antennules and antennae. Following the maxillipeds are 
three pairs of buds to represent the first, second, and fifth pairs of thoracic limbs. The fif^t bud 
consists of a single branch, which is shown by its snbsequent history to be the exopodite. The 
second has two branches, a short exopodite, and an extremely short endopodite, while the third 
consists of a eomewhat longer, but still rudimentary, shaft, which represents the endopodite of 
the fifUi 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 undi- 
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 line, 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. | ,^,^^-^1^ 

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MEMOIRS OF THE NATIONAL 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 xvi, Fig. 1. It is also 
shown, much less enlai'ged, in side view in PL xvii, Fig. 1. The first and fifth thoracic 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 present in 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 marginal 
hairs of the earlier stage and is now simple, while two plumose hairs have made their appearanci^ 
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 joiut, and the long terminal hair which it carried at the earlier stage 
has disappeared. The mandibles, maxilla, and maxillipeds are about as they were before, but the 
endopodite of the third maxilliped 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 twolobed 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 antennaB when the appendage is in the posi- 
tion shown in the figure PL xvi. Fig. 1. The appendage seems to have little power of motion and 
it seldom deviates much from 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 l^ve 
have as yet no traces of appendages. The first four somites are short and equal, the fifth is 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 considecable sizo, 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 Alpheun 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, it did not seem to be advisa- 
ble to make new figures, and in the remainder of the description the illustrations which are* 
i:eferred to actually represent the larvae of other species. After it« third molt the larva of 
Alphem minor passes into its fourth stage, when it becomes almost exactly like the fourth larval 
stage of Alpheus heterocheliSy shown in PL xvm, 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 nuwle 
their appearance in the basal joints of the antennules. The mandible has lost its outer branch, 
and the basal joint of the second maxilla, PL xvi, Fig. 5, carries on its inner edge three hairy lobes. 
There are now five i)air8 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 



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304 MBMOIBS OP THE NATIONAL ACADEMY OF SCIENCES. 

and those of the first and second thoracic legs. The endopodites of the maxillipeds are as before. 
The endopodite of the first thoracic leg, which was represented in stage three by a radimentary 
bad, now appears to be entirely wanting. The second thoracic limb, which in stage three was 
^'presented by a bilobed bud, now consists of a basal joint, with a large, fonctional, plamose 
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 fonrth thoracic 
limbSj 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 abont 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 becon^ 
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 larvje of other species exactly represent the larva of AlpJieus 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 'maxiUipeds 
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. xxi. 
Fig. 1, from which, however, it differs greatly as regards the telson and the sixth abdominal ap- 
f>end'rige. The first five abdominal appendages are now represented by buds like those shown in 
PI. XXI, Fig. 1, and in PI. xix. Figs. 1 and 2, but the terminal portion of the abdomen is nearly like 
that of Fig. 3 in PI. XX. The telson is greatly elongated, • narrow, and its terminal spines are 
very small. 

THE OLDBB LABYAL STAGES OF ALPHEUS KINOB. 

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

THE MBTAMOEPHOSIS OP ALPHEUS HETEBOCHELIS FBOM THE BAHAMA ISLANDS. 

In the Bahama Islands this species passes through a series of stages which, except for a few 
minor difierences 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. 

FIBST LABVAL STAGE. 

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

THE SECOND LABVAL STAGE. 

Uke Alpheus minus the Bahama, specimens of Alpheus heferochelis molt within a few houife 
after hatching, but they undergo no essential change, and PI. xvi, 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 ^airs 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 PI. xvi, Fig. 3. In both sppciea 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 



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MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 365 

telson are mach more nearly equal to tbe others in Alpheus heterochelis than in Alphetut minor. If, 
as seems probable, the triangalar telson of the macroiiran zoea 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 Alphetu heterochelis. 

THE THIRD LARVAL STAGE. 

This is shown from below in PL xviii, Fig. 2, and a comparison with Fig. 1 of PI. xvi will show its 
very close resemblance to Alplie^is minun 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 
Alpheu8 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 xvin, 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 xix 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 PL 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 Alplieus 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, is 
shown in side view in PL xix. 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 maxillic 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 xix, 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 
^act 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 PL XYi, Fig. 5. 

The three pairs of maxillipeds (PL xix. Fig. 1) are almost exactly like those of the newly 
hatched Bahama larva (PL xviii. Fig. 1) or those of the Alpheus minor at the same stage (PL xvi, 
Fig. 2), but the thoracic appendages (PL xix. 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 



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366 MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 

functionless. Careful exaoiinatiou sbows that there are tive pairs (the five pairs of thoracic limbs), 
and that all but the last pair are biramous. lu all, the exopodites are longer than the cndopodites, 
which decrease in length from in front backwanls, 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 tc^lson 
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 preseuts a most important differc^pce from that of the young 
Bahama larva, as it is not triangular, but spatulate ; and of the eight pairs of setie the three pairs 
which in Alphem 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 setie. 

This larva molts a few hours after hatching, and at once undergoes the most profound changes, 
and assumes the form shown in PI. xx, Fig. 3. It is no longer a larva, but a young Alpheus. 
The eyes are almost covered by the carapace, the ear is well developed, and all the ap|>endages are 
present and functional and essentially like those of the adult. The antennule has two fiagella, 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 has4ts 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 fiat plate with cutting lobes and a 
short, rod-like endopodite. The three pairs of maxillipeds ( Figs. 7, 8, and 9) have a^u iied the char- 
acteristic Macrouran form and are no longer concerned in locomotion, while the thoracic limbs have 
elongated into the five i>airs of ambulatory ap[>endages of the adult, although they still retain 
their rudimentary exopodites. The abdomen is noiv like that of the adult, and the telson (Fig. 
4) is long and narrow. An older specimen is shown in Fig. 2 and a still older one in PL xvii. Fig. 3. 

Comparing the history of the Bahama form with that of the North Carolina form, the most 
conspicuous peculiarity, and that which firsit attracts attention, is tLe great abbreviation of the 
latter. The Beaufort specimens hatch in a much more advanced condition than the Bahama si>eci- 
mens, and, 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 no 
exact parallel caube drawn between any larval stage of the one and a stage of the other. The 
statement that the Beaufort specimens pass, belbre leaving 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, aild then seven schizopod feet 
with functional swimming exopodites, while the Beaufort form never has more than thi'ee. As 
regards the thoracic region and the first five abdominal appendages the Beaufort larva, at the time 
of hatching (PL xix, Fig. 1), is more advanced than the fourth larval stage of the Bahama form 
(PL xviii, Fig. 3), while the sixth pair of abdominal appendages are like those of the Bahama form 
at the time of hatching (PL xyi. 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 lieterochelifi which occur at Key West 
differ from those which occur at Beaufort in about the same way that the latter dififer from those 
from the Bahamas, as the metaraoq)hosis 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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MBMOIES OP THE NATIONAL ACADEMY OF SCIENCES. 367 

chelsB, 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, bat, 
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 anil Nassau showed 
the closest agreement in nearly all particulars (v. Chai). v, Pt. First, Section u), and it has there- 
fore seemed best for us to regard them as belonging to a single species; the more so since our 
discovery that different individuals of another species found at Nassau {Alphetis 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. 

Alphetis 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 saulqfi just ready to hatch is shown in PI. xxi, Fig. 5. The large claws are 
plainly visible through the transparent shell. The antenna) 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, = ^^ 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 
PI. XXI, Figs. 4, 6, 7,9, and PI. xxn, Figs. 1-8, 12. In both varieties the animal hatched o^ 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 larvae being in a stage corresponding to that usually at- 
tained after the second molt and represented in PI. xxi. Fig. 8 This is referred to again at 
the end of the section. 

To return to the first larva (PI. xxi, 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. Eudimentary gills are present and a remnant 
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 xxn. 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 antennae are biramous and jointed. The anteunules (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 antennae 
(PI. xxu, 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 maxilldB (Fig. 6, 



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368 MEMOIBS OP THE NATIONAL ACADEMY OP SCIENCES. 

shown with more detail in Pig. 3, PI. xxii) have adult characters. They are biramous. The endo- 
podite is stoat and toothed at its apex. The more slender outer division bears a short spine 
near the distal end/ In the second maxilla (Fig. 6, PI. xxi) the scaphognatbite or respiratory 
plate is most prominent This is now composed of an anterior portion, bordered with from six to 
twelve long plumo^ hairs and a posterior, rudimentary, and hairless lobe. The inner division 
(endopodite) has the adult form, while tbe innermost lobes of the adult appendage (PI. xxiv. Fig. 
9) are unrepresented. 

The maxillii>^s are all biramous appendages, and their exo|>odites 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 equal in length to the exoi>odite. In tbe first i>air of thoracic 
legs (PI. xxi, Figs. 4 and 7) the inequality of tbe cbehe is very marked, and, as we have alrea<ly 
seen, it is so for some time before hatching. Individuals differ somewhat in this respect. Tbe 
articulations of the carpus and meros are distinct. The exoiMKlites of this and of the three suc- 
ceeding pairs of thoracic limbs are tipped with rudimentary invaginated hairs. The second pair of 
pereiopods (PI. xxii, Fig. 1) are chelate, but tbe articulations of tbe carpus are not distinct. Tbe 
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. Tbe first pair (PI. xxii, Fig. 5) consist 
of a larger outer and smaller inner blade. This endo[>odite remains rudimentary in the adult 
male, but nearly equals tbe exopodite in length in the female, as will be seen by reference to PI. 
XXIV, Figs. 4 and 5. This convenient sexual mark probably api>ears i?arly, but can not Iw relied 
upon at tbis stage. Tbe second (PI. xxii. Fig. 4) and tbree succeeiliug pairs of pleoixMls have a 
stout base, an outer blade like that of tbe first pair, and a sborter endoi>odite which bears on its 
inner margin a lobule or palp. The sixth i)air, or uropods (PI. xxi. Fig. 9), are not yet free. The 
inner and smaller divisions point forward, meeting on tbe middle line. The telson, wliicb termi- 
nates the body, covering tbe outer nropodal limbs, is a rounded, spatulate plate, with a median notch. 
It^ free posterior edge is fringed with seven pairs of plumose spines, tbe first or median pair l»eing 
rudimeuUh*3% and the next four succeeding pairs long and nearly equal. 

Second larva (length, i\ft, inch). — Tbe first moult takes place either imniCiliately or very soon 
after hatching. Tbe animal as it now appears is shown in PI. xxi, Fig. 2. Tbe principal external 
changes thus produced are tbe following: (I) Tbe rostrum and ocular arcbes extend fartlier over 
tbe eyes. (2) Both divisions of tbe autennules are considerably extended. Tbe flagella of the 
antennae are from three to four times their former size and are articulated into twenty to thirty 
rings, tbe scale still not passing tbe peduncle. (3) Tbe thoracic appendages have more of the 
adult characteristics. Tbe articulations of the carpus of tbe second pair are distinct. The exo- 
podites of tbe first four pairs are functional, and tbe last pair bas grown forward. (4) The 
pleopods presently acquire swimming hairs^ tbe telson plate is free and tbe uropods are func- 
tional for the first time. (5) The last thoracic segment is still uncovered and tbe eyes are 
incompletely hooded. 

Third larva (length, about i inch). — Tbe thjrd larv^a as it api>ears after the second moult, 
which takes place in twenty-five to thirty hours after hatching, is represented in PI. xxi. Fig. 
8. It has now the general adult character, and can not be called a larva in tbe 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 carrie<l 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. Tbe gills are now quite prominent. They are evidently functional to 
some degree, and were so, possibly, at an earlier date. Tbe yellow and red pigment cells have 
nearly all disappeared or are temi)orarily 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 sur|)asses the scale, 
and its flagellum nearly equals the carapace in length. As in the adult, the large chelae are very 
I>rominent. Tbe 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 xxi. 



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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 antennse of this 
phase are given in Figs. 9, 10, 16, PL xxii. The inner branch of the antennnles is still relatively 
short; the basal or aural spine extends to nearly the end of the first joint. The bristle- bordered 
plate of the antennsB 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 may 
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 fomi (after fqurth moult). — ^These animals moulted the fourth time ten days after 
hatching. Very little change was apparent, except in sizcj and beyond this point we did not follow 
them. 

METAMORPHOSIS OF ALPHEUS SAULOYI FUBTHEB ABBBETIATED. 

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 batched 
in a glass dish April 25 (Fig. 17, PI. xxii). The prawn (var. longicarpm) was taken from a brown 
sponge. The eggs, half a dozeii in number, were slow in developing. The small chela is shown 
in Fig. 16. 

This phase corresponds with that usually attained after the second moult (shown in Fig. 8, 
PI. XXI), 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 



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Y. 



ALFHEUS: A STUBT IH TEE DEVELOPMEVT OF CBTOTACBA. 



By Fbanois H. Hebbick. 



CONTENTS. 



Introdoction. 
Methods. 
Part First : 

I. The habits and Solor yariations of Alpheos. 
11. Variations in Alpheua heierocheliM. 

III. The abbreviated development of AJpheas and its 

relation to the environment. 

IV. Theadnlt. 

V. Variations from the specific type. 
VI. Measurements. 

VII. The causes and significance of variation in AU 
pheut saulcyi. 
Part Second : 

I. Stracture of the first larva of Alpheus saulcyi. 
The origin of ovarian eggs in Alphens, Homams^ 

and Palinnnis. 
Segmentation in Alpkeua mintu. 
The development of Alphens. 

First stage: Segmentation to formation of blas- 
toderm. 
Second stage: Migration of cells from blastoderm 

to the interior. The invagination-stage. 
Third stage: Optic disks and ventral plate. 
Fourth stage: Thickening of optic disks. Ka- 
di men ts of appendages. 
F\fth stage: Radiments of three pairs of ap- 
pendages. Optic disks closely united by 
transverse cord. Degenerative changes. 
Sixth stage: The egg-nauplius. • 
Seventy stage: Seven pairs of appendages 
formed. 

[With thirty 



II. 

III. 
IV. 



Part 8sconi>— Continued. 

rV. The development ofOklpheus — Continued. 

Eighth stage: Nine pairs of appendages present. 
Ninth stage: Eye-pigment formed. 
Tenth stage: Ganglia of ventral nerve*oord 
distinct and completely separated from the 
skin. 
Eleventh stage: Embryo about to hatch {AU 

pheus heterochelis). 
Twelfth stage: First larva (Alphtus saulcyi). 
Thirteenth stage: Young Alpheus, four to ten 
days old. 
V. Notes on the Segmentation of Crustacea. 
VI. Cell Degeneration. 
VII. The Origin and History of Wandering Cells in 

Alphens. 
VIII. The Development of the Nervous System. 
IX. The Eyes. 

The median eye of the larva and adult. 
General anatomy of the eye-stalk. 
Structure of theiommatidium. 
Arrangement of the ommatidia. 
The development of the compound eye. 

(1) Origin of the optic disk. 

(2) Development of the retina and the 

optic ganglion. 
The eye under the influence of light and dark- 
ness. 
X. Summary of Part Second. 
XI. References. 

Explanation of figures (accompitnying each plate), 
-eight plates.] 



INTEODTJCTION. 

The observations offered in this memoir were nndertaken at Beaafort, Korth Carolina, in 
Jnne, 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 counst*!, 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 larvae or first zo<^ have been hatched 
in aquaria. Many of thesp forms are new or but little known, and when the means of publication 
is found it is hoped that their comparative and systematic zoology can be fully illustrated. 



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MEMOIRS OF THE NATIONAL ACADEMY OP 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 thiit 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 Arthroi)od8 is very great, commensnrate 
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 
natnre. 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 only partially carried out. T\xk early stages of Stenopus hispidus^ 
Homarus AmericanMS, and Pontonid domestica have, however, been followed, and less completely 
those of Bippa talpoides and Palcemonetes vulgaris. 

Spence Bate (3) states that the shortened development of Alpheus was first described in his 
memoir, with dmwings, 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 Zoea.'^ 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 oiAlpliem minus, Say. An inspection of this drawing (3, PL oxxii, Fig. 1) 
leaves some iloubt 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 descrilie 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.^ninus) 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 much further advanced toward 
the adult state than is the first zoea 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). 

METHODS OF WORK. 

Several species of prawns, such as Stenopus and Pontonia, repeatedly laid eggs while kept in 
aquaria, and doubtless I should have succeeded equally well with Alpheus, if sufficient pains had 
beien taken. As it was, only two or three individuals gratified me in this respect, but in e^ch 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 or age of the embryo. By obtain- 
ing a number of series in this way the whole life history within the egg could be followed, and by 



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372 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCBa 

this meaDS 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 we rely upon material taken by chance. 

Experience with the nseof Perenyi's fluid in preparing the eggs led me to discard this reagent 
altogether, and to substitut^e for it Eleinenberg's picro-snlphuric 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 tbe 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 
haemotoxylon. They were afterwards shelled, when this was possible ; saturated with paraffin by 
the turpentine-paraffin method, and were then mounted. While the paraffin was congealing they 
were carefully placed in i>osition with a hand lens. This last important and often troublesome 
process was rendered easy by the diflerential proi>erty of the stain, which aftects 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 ap|>ear 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 similafly treated. All 
drawings which represent surface views excepting Pig. 10 were made from objects thus prepared. 
' In general, Kleinenberg's hnemotoxylon 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. Gallic's 
quadruple stain of hsemotoxylon, 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 alcohol. 

Pabt Fiest. 

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 8ay, from Beaufort, N. C, A. heterochelis Say, from Beaufort, N. C, 
and Nassau, New Providence, and A. saulcyi^ from Nassau, New Providence. Tbe 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 stndyiDg the development of the lobster, ^hich has also a large egg, I have found it necessary to adopt new 
methods, especially in the treatment of the eggs for surface preparations. In most cases the egg-membranes are best 
removed by the aid of hot water. ^ 

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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 beautiful 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. wehsteri Kingsley), first reported from Florida, was also discovered on Green 
Key reef, a. few miles from Nassau. 

From collections which I made at Abaco and Andros Islands, I am led to brieve that the 
different species are quite generally distrib;ited 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 ife clusters of algae, 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 can, 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 fnsilade is kept up along some 
of the shores at low tide. This snapping propensity is shared Jl)y both sexes whether in or out of 
the water, and it is undoubtedly correlated with their pugnacious 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 like 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 o|)ened 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 forcible 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, f 



* This species is entirely new. The large concealed claw snggests a poison apparatns. The " fingers " are ex- 
ceedingly slender and sharp at the points. Althongb kept for over a week in an aquarium it emitted no sonuds. 

t According to Wood-Mason sonnd-prodncing organs in Crustacea were first brought to notice by Hiigendorf, in 
V. der Decker's "Roisen in Ost-Africa (Crustaceen)," and were afterwards observed by himself in his dredging ex- 
pedition to the Andaman Islands. The stridnlating organs—scrapers and rasps — may be either on the carapace and 
appendage^ or on the appendages alone. 

t 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 propodns, when the tooth of the dactyle is not pnlled out of its socket but driven int^o it. None of the conditions 
of piston movement are present. The walls and floor of the pit are relatively soft, while the tips of the claw are 
deuse aud stony. The "click" can be artificially produced when the claws are clamped with rubber, whether the 
** stopper" is present or not. 



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374 MEB101E3 OP THE NATIONAL ACADEMY OP SCIENCES. 

In AlpJieui heterochelis the dactyle of the large pincers is a curved blade which shats down 
into a groove on the oocludent margin of the '< thumb," and closes over the latter like a pair of 
sheacs. 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 ^Hhnmb," 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 resnlt, 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 fireely in and out the well^ and not like a *' tightly packeci 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 *Hhumb" and ** finger," and I have frequently seen specimens of A. heterochelUj 
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 
claw is not used as a clasper, but as a saber. The sharp external edge is 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, Hircinia arcutaj which is not to be mistaken, grows on the shallow 
reefs and ofif 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 I^ feet in 
diameter. There is commonly one, sometimes two, large exhaleut 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. If a sponge colony of this kind is pulled and torn apart, one is certain 
to find it swarming and crackling with a small si>ecies 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 chelae, 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 attaehed 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 out 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 difler 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. 
In both sexes the large claws are bright red (v. PI. iv, and for details section iv). 

The female is practically inert during the breeding season, and at such times is well proteeted 
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 
^ fix)m 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, numl)er, and color of the eggs. t 

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Habitat of Alpheas. 


Length of 9 . 


Namber of 


Diameter. 


Color. 


Color of adalt. 


Brown sponge... 
Green sponge 


Inches, 

i 

lA 


19 
347 


Inches. 


Yellow (variable).... 

Usnally green ; in 
this case yellow. 


Large ohela),red (bine 

or brown in others.) 

Large chelso, orange- 



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, Alphem saulcyij On6rin, it is necessary, for descriptive purposes, to distin- 
guish two varieties, viz : 

Alpheus saulcyiy variety longicarpus (from brown sponges), 
Alpheus saul&yiy variety breviearpus (from green sponges). 

These two varieties shade completely into each other by numerous intermediate forms. The 
longicarpu8 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 breviearpus 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.* 

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, algse, etc. 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 known 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 Alphem 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 egg^ 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. 

Alphetis 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 fonnd on both the varieties, bat 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 carious 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 tbe embryo, is packed fall of them. (v. Fig. 199 and section iv, Part Second.) 

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

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376 • MEMOIES OP THB NATIONAL ACADEMY OP SCIENCES. 

exposed at low tide. Alphem minwt has a similar eiiviroDment and is similarly colored. Alpteu$ 
keterochelis from Nassaa, New Providence, on the other hand, lives under loose stones, amid the 
white coral sands of the beach, and is noticeably transparent, lookinp: oh if the color bad been 
bleached oat of it. The body is sprinkled with dots of brown pigment. The claws and legs are 
pale greenish. Toang and old are invariably colored alike. 

In a collection of adalt Alphens of either sex of the same or of several s|>ecies, where there is 
a difference in size of the large claws, it is notice<l that either the right or the left, indifferently, 
may be the greater. As we will see, this differentiation of the chela* begins in one instance before 
the animal is hatched. Is this right and left handed condition to be explained by inheritance 
from the parents t In about forty lapv© of a small broo<l of Alpliem Maulcyi^ all invariably had the 
left claw enlarged, and in a smaller number (all that were preserved), from another female of the 
same si>ecies, 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 callfHl to the subject while at the 
seashore.* 

The breeding 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 In^gan earlier and lasted considerably 
later.t There the temperature is high and remarkably constant, the annual range being about 15^ 
(temperature of air TCP P. in March, 80^ in June), and in conse<iuence the early phases of devel- 
opment are rapidly i)assed. Not one prawn in a hundred was found with eggs in an earlier stage 
than that of yolk segmentation. 

11. — VARIATIONS IN ALPHEUS HETEBOOHELIS. 

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 zoologists might regard as of specific value, but they are no 
greater than we have proved to exist among individuals of the same si>ecies 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 fbrm is relatively shorter and thicker in 
both sexes. Both lingers are nearly cylindrical, and covere<l with hairs, which are distributed 
either singly or in tufts. In the Beaufort heterochelift 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 iis 
usually longer and slenderer. The dactyle is about one-half the length of the proi>odns. 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 setae. Similar rows of setje occur on the sides of the o()posing 
" thumb." 

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



• Mr. J. J. Northrop, of Colombia College, while at Nassau in the winter and spring of 1890, kindly offered To 
collect for mo some specimens of AlplteuasauJryi 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 larvas from the *Moggerhead'* 
sponge. In the first instance the left chela was the largest in the mother and in each of the sixteen young. In the 
latter, two ha<l 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. 






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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. 

HL—THE ABBREVIATED DEVELOPlOiNT 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 grou[)S, 
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 
moderof life, and the variations thus entailed have led to the production of the zoea, a locomotor 
larva, fundamentally different from the adult. We may regard the zoea as a secondary, adaptive 
form, directly descended from an ancestral protozoean 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 zoeal 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 
zoea-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 nonparasitic and has a complicated metamorphosis^ while the same 
species from another locality isparoMtic and lias 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 — 

r Alpheus heterochelisj from Nassau, New Providence. 

(1) } Alpheus heterocheliSy from Beaufort, North Oaralina. 
( Alpheus heterochelisj from Key West, Florida. 

(2) Alpheus saulcyi, from Nassau, New Providence. 

ALPHEUS HETEROCHBLI8 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. 

Mrst 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. 



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378 MEMOIES OF THE NATIONAL ACADEMY OP SCIENCES. 

The antennules consist of a stout jointed stalls, the terminal segment of which bears four 
sensory filaments. A long plumose spine springs from the extremity of the second joint on the 
inner side. 

The antennae are biramous, the two branches arising apparently out of a common basal segment. 
The outer division is a scale-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 in a 
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 zoeal 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- 
tary 'y 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. 

ALPHSUS nKTEROCHBUS FROM BEAUVORT. 

The peculiar metamorphosis of the Beaufort HetertwJielis was described in 1834 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 pairs 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 api>ears only after 
several months. 

ALPHBUS UETEROCBKUS 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. The anteunie 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 disproiK)rtionately so as in the adiilt 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 the adult. There were five pairs of abdominal feet or swimmerets, each 
with endopodite and exopodite, like those of the second larval stage of the lobster." 

ALPHBUS 8AULCYI 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 t^gg in the full adult form. 

Comparing the histories just given with the one before us, we find that the first larva of 
Alpheus 8aulcyi 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 Alpliei, 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 ^ 

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379 



size and number of the eggs. These and the other facts which we have been coiisiderin<r are 
given in tabalar view below : 



Species. 


Habito. 


Metamorphosia. 


Namber 
of eggs. 


Diameter 
of egg. 


LanfCth of 
fvroale. 


Alphens niinns (from Beaufort). 
A. heterochelis (from Nassau) . .. 
A. heterochelis (from Beaufort) . 
A. heterochelis (from Florida) .. 
A. sanlcyi (var.-brevircarpus) ... 
A. saulcyi (var. longicarpus).... 


Non-parasitic 

•do ...... . ....... 


Complete 

....do -. . 


•500 
300-500 
150-300 


Inch. 


Inehet. 
i-1 

1-lt 


.do 


Ahridced 


demi*Darasitic . . . _ . . 


do 


Completely parasitic. 
....do ............... 


Nearly lost 

Completely absent 
(in some cases). 


100-350 
5-20 


,'.4 


t-l' 





* 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. mulcyi 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 Alpheus we thus have several stages in the abbreviation of the metamorphosis 
between the macrouran zoea stage and the adult form. What is the cause of this gradual suppres- 
sion of the zoea like form ? Tlie conclusion seems to be unavoidable that in the Babaman 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 semiparasitlct 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. If the zoea brood were swept out 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 larvae of this Alpheus are never carried far 
from the shores, but while they undoubtedly leave the sponge in which the}'^ are born, they prob- 
ably establish themselves very soon in a new one. (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 
becom.e 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 reestablished. 

No fewer than three species of macroura, together with the Alpheus above described, occur in 
the large brown sponges {Hlrcinia arcula) of the Bahama islands. These (one of which is also^ an 
Alpheus) live in the larger oscula, are less regular in their occurrence, and evidently have not 
adopted a stationary parasitic life. In none of them is the metamorphosis of the larva abbreviateil. 
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 Oephalopods among the MoUnsca, to reach the adult conditions rapidly by omitting some of 
the early embryonic stages. 



* An egg of J. saulcyi var. longicarpm^ jnst ready to hatch (PI. xxi, Fig. 5), measures j^^y by xHy 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. 



Digitized by 



Ljoogle 



380 MEMOIRS OF THE NATIONAL AOADKMY OF SCIENCES. 

An abridged larval developipent bad been attribated to tbe following macroara: Tiie lobster 
Homarusamericanus; the crayfishes] Hippolyte polaris; PaUemoneies variann; Palwmon potiuna; Pa- 
Icemon adspersus and Eriphia spinifrons (as first observed by Uatbke, according to Packard ) ; Bytho- 
caris lemopsis (observed by G. O. Sars, according to S. I. Smith) ; Alpheus heterochelis^ and A. ttaulcyi. 
To this h'st we must probably add the names of many deep-sea decapoda, Munidopsis, Olypko- 
crangoHj Elasmonotus inermis^ Sabinea princepsj Acanthephyra gracilUj and Ptmphae princepn^ as 
inferred by S. I. Smith, on account of the extraordinarily large si»e of their eggs. An egg of 
remarkable dimensions is that of ** the little shrimp {Parapaniphae sulcatifranSy) 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 which the egf^ is relatively 
nearly as large as in many birds!" <' Although the great size of the eggSj^ 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 (50)." 

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 Palamonetes 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 larvas, and, like 
them, swim at the.surface of the ocean. S. I. Smith {58) and Byder (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 the antennae are somewhat rudimentary. 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. Tbe 
flagella of the antennae 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 swim- 
raerets are developed in the seventh stage, at the end of which there is a decided diflFerence 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 saulcyi (Fig. 8, PI. xxi) as it appears twenty-four 
hours after hatching, but the latter has the more decided adult characters. The young Alpheus 
is fnrther 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 
Palwmonetes variant 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 Alphetis saulcyij where we have the same specicis 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 {Oegarcinus 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 JEglea ('' mountain crab"). 



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

Digitized by LnOOQ iC 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 381 

The habits of the hermit crabs, though secondarily acqaired 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 Fontonia domestical which lives in the mantle cavity of 
several species of Pinna, has in no way affected its development. 

IV.-— THE ADULT. 

The Alpheus whose development has just been traced was provisionally named Alph&usprce- 
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 GuiSrin in Eamon de 
la Sagra's History of Cuba (18). In Gu6rin's drawings the long spine (squamal spine) of the 
anteunsB 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 bf 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 Gu6rin's name. 

The systematic zoology 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 identify 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 saulcyi resident in certain green 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 ; smaU 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"", S 5 largest, 42"", 9 ; average length, 25 to 
30"". Females exceed the males a little in length, and greatly surpass the latter in size when 
swollen with their eggs. 

Color: The color of this form is shown in PI. iv. 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 these 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'' 5 eggs and ovaries of female golden yellow. Length of 9 , 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 

Digitized by LnOOQ iC 



382 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

ocalar spines. The rostmni is short, subaoate, broa^ler at base than long, feebly convex aDove, 
withoQt crest. The orbital spines are separated from the rostram by a shallow su|>eriicial groove, 
and the marginal notch on each side has a regular V'S^^P^ oatliue. Length of spines and width 
of notch are slightly variable. 

The lateral compression of caiapax is not marked. Frontal angle (angle made by middle line 
above and below rostram, greater in 9 than in 3 . In some females with the carapace bulged oat 
by the ovaries the angle is as great as 45^. In males without conspicuous '< forehead" frontal 
ang]e, lOo. 

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 i>osterior extremity on either side the middle 
line, and two (or more) separate spines uiK)n 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 (PI. XXII, 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, situate<t below the compound 
eyes and between the bases of the antennules. 

The antennules (Fig. 4, PI. xxiii) consist of a three-jointed stem or protopodite, an exoi>odite, 
and eudopodite. The first segment of the stem is largest dnd 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 seta*) are borne, distrib- 
uted in seven to ten bunches of two to three in a bunch. 

The auteunsB (Fig. 8, PI. xxiii) are cbint>08ed of three parts — a basal i)ortion ([irotopodite), 
which carries a squamous spine (exopodite), and on its inner and lower side a long 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 seta). The antennal stem or peduncle consists of two short proximal segments and a long 
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 dififerent parts for an average 
specimen is shown in Fig. 8, PI. xxiii, and in PI. rv. 

The mandibles (Fig. 3, PI. xxiii) are strongly bifurcate, 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 (PI. 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 (Pi. xxiv, Fig. 9) is composed of three portions. (1) The long respiratory 
plate; the "bailer'^ or scaphognathite, fringed with a row of setae. (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, PI. xxiii) are made up of a long, strap-shaped exoi>odi 
with jointed setae at the extremity and a small setigerous plate at its base; a small, two-jointed 
endopodite, protopotlite, and epipodite. The protopodite is divided by a fissure into two lobes, a 
larger (basipotlite), 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, i r^r^rvT^ 

igi ize y ^ 




i^ 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 383 

The second pair of maxillipeds (Fig. 0) has a long, strap-shaped exopodite, like that of the 
first pair. The eudopodite is incarved, and segmented into at least four parts. The dactylopo- 
dite or terminal segment is the longest, and is thickly stadded with serrate bristles and setie. 
There is a small oval epipodite. 

The third pair of maxillipeds (Fig. 5) consist of a basal piece (coxopodite) and a long two- 
branched appendage. The large branch consists of three distinct 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 ec^ual to it in length. The lower surface of the two terminal joints is covered by 
numerous transverse i-ows 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 chelae (^' hands" or "shears''). 
The chelsB are very unequal. Large claw (relatively larger in S ) 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, PI. xxiv) usually carried bent downward. Fingers nearly equal; three- 
fourths as long as palmer portion of hand; bent slightly downward and outward; jiropodus sub- 
cylindrical; half as broad as long; tip simple or slightly bifid. Small bunches of setsB on fingers. 

Second pair of pereiopods (Fig. 1, PI. xxiii) : 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+4+6.' Second, third, 
and fourth of nearly equal length; fifth equals 2+3. 

The third, fourth (Fig. 2, PI. xxiii), and fifth pairs (Fig. 1, PI. xxiv) 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 seta? 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 mark's of distinction. The first alxlominal 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 fringetl with long setae. 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. 6) the modification has not proceeded so far. 
The endopodite is here the shorter and has no secondary branch. In the very young forms 
(first larvje) these appendages appear to be nearly alike in both sexes (PI. xxu, Fig. 5). 

The uropods or sixth pair of pleopods hardly require special notice (PI. iv). The endojKKiite, 
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 setae. ^ 

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 Longicarptis: 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 



t- Digitized by 



Ljoogle 






384 MEMoms OP the national academy op sciences, 

individaala found in tbem belong to this variety. Tbe color variations of this form have already 
been given in section i. 

The rostrum is sometimes wanting, as in the individual fh>m which Fig. 11, PI. xxii, 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 ol forms, which are placed by Dana 
in a separate genus (BeUens). 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 (20). 
The structural |K)ints of difiference between the longicarpus and the other form lie chietly in the 
antennaB and first pair of walking legs. These may be seen by a comparison of Figs. 11, 13, 18, 
PI. XXII, and Fig. 2, PI. xxiv, with Figs. 4, 8, PI. xxui, and Fig. 3, PI. xxiv. 

In the first pair of antennse the aural spine (Fig. 11, PI. xxii) 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. hreviearpus) the aural spine (Fig. 4, PI. xxiii) 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, PI. xxu) ; an inferior and outer basal spine, and a slightly longer one, 
the squamous spine^ articulated to the joint carrying the latter. There is 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 npi)er surface of the segment bearing the basal spine, near the articulation. 

In variety hreviearpus (Fig. 8, PI. xxiii) the squamous spine is stout andreaches 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 setiv; scale not quite as long 
as spine. The inferior basal spine not one-half the length of the squamous spine. There is a 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, PI. xxrv) is short 
and broad. The finger ends in two or three homy 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 relatively very long, quite as long as 
the palmar portion of the propodus. 

In the hreviearpus the small chela is long and somewhat narrower (Fig. 3, PI. xxiv). Tips 
of fingers usually simple, but sometimes notched^ the peculiar tuft of hairs is wanting. Carpus 
relatively short ; ^out one-third the length of the palm. 

The large chela of the longicarpus may also differ noticeably from the hreviearpus type. (Com- 
pare Fig. 8, PI. XXIV with the figures on PI. iv.) 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 thumb with claw-like 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 nnmt>er of individuals of this species have the characteristics of the two 
varieties just described, but about five 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 antenuular 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 i)ropodus of the small chela of the first pair of pereiopods ; (4) 
the length of the carpus of the small cheliped ; (6) the general shape and character of the large 



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

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



385 



claw. (1) With respect to the first point, we meet with a perfectly graduated series between Ihe 
two extremes (Figs. 11, 18, PI. xxii, Figs. 4, PI. xxiii). (2) The same is true of the relative lengths 
of the antennal spines, the scale, and peduncle (Figs. 11, 13, 14, PI. xxn). In Fig. 11 there is no 
evident scale and the spines are nearly equal. In Fig. 14 the spines are markedly unequal, $ind 
there is a rudimentary scale. In Fig. 13 this scale is further developed. (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 
setse 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. 

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

Table I. — Shotoing variations in Alphcus saulcyi and the intermediate stages between the varieties 

brevicarpus and longicarpus. 



No. 


Sex. 


1 


^ 


2 


9 


3 


(? 


4 


<? 


6 


9 


6 


9 


7 


9 


8 


<? 


9 


(? 


10 


^ 


11 


<r 


12 


^ 


13 


^ 


14 


<? 


15 


9 



Habitat 



No. 



Green ajwDge 

...do 

Brown sponge 

Oreen sponge 

Rocks; DixPt. reef- 

do 

do 

Rocks; Hog Id. reef. 

do 

Rocks; Green Key 
reef. 

Brown sponge 

do -.1 

Rocks; Dix Pt.reef. 

Brown sponge 

Reef rocks 



Length. 



mm. 
29.7 

42 

9 

9.5 
17 

10.4 
11.6^ 
10 
10 
9.5 

17.5 

13 
9.5 
5.5 

11 



Aural spine. 



Extends f length 2d seir- 

inent of antennnlar stalk 

Toil. 2d segojent 

do ..n 

do 

i ]. 2d segment 



do 

1. of Ist segment 

Over i 1. of 1st segment ... 
Nearly to end 1st segment, 
f 1. 1st segment 



Nearly to end Ist segment. 

do 

i Ist segment * 

do 

Nearly to end Ist segment. 



SqnamoQB spine. 



Extends nearly to end of antennn- 
lar stalk. 

Do. 

Do. 

Do. 
Extends nearly to end of antennal 

stalk. 
Not nearly to end of antennal stalk. 

Do. 
f 1. antennal stalk. 
More than ^ antennal stalk. 
Nearly to end antennal stalk. 

i antennal stalk. 

More than i antennal stalk. 

Do. 
f 1. antennal stalk. 
f 1. antennal stalk. 



Inferior basal spine. 



I length squamons 
spine. 

Less than i 1. squa- 
mous spine. 

....do 



-...do 



Nearly | 1. squa- 
mous spine. 
do 



i 1. squamous spine, 
fl. squamous spine. 



More than ^1. squa- 
mous spine. 



Nearly as lon^ as 

iquamous spine. 

....do 



Sqnaine or scale. 



Scale as long as 
squamous spine. 



Scale nearly as 
Ion g as squamous 
spine. 

Scale somewhat 
shorter than 
squamous spine. 

Scale not quite 1. 
squamous spine. 

Small and rudimen- 
tary. 

....do 

Rudiment 

....do 



Rudiment (hardly 
visible). 

Rudiment 

No scale 

....do 

....do ..^ 



.do 



Carpns of 
small chela. 



Short 
...do .. 



..do . 

..do . 

Long. 
..do . 



Short 
Long.. 

...do *. 



..do 
..do 
..do 
..do 



.do 



Fingers of small chela. 



Tips simple; no 

on dactyle. 
Tipssimple;n< 



• tuft 
no tuft. 



.do 



.do 



Tips simple; nidi 
mentary tuft. 

Prongs : tuft on 
dactyle. 



Tips simple; no tuft 
Prongs and tuft 

Propodus ends in 
prongs. 

Prongs and tuft 

do 

....do 

....do 



.do 



Remarks. 



Type of var. brevicarpua, 
V. drawing, PI. iv. 
Claws dull red. 



Combines characters of 
both varieties. 



V. Fig. 13, PI. XXII. 

V. Fig. 14, PI. XXII, (outer 

antennte from above). 
Dactyle missing. 

Claws reddish orange. 

Type of var. longicarpus. 
Rostrum wanting. 

Claws bright blue; dactyle 
of small chela extends 
imm beyond propodus. 



S. Mis. 94 26 



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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 l^To. 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 anteuular stalk. 
The inferior basal spine is rather less than one-half the length of s<iuamous spine ; npi>er basal spine 
a rudimentary knob. The squamous spine has a well-developed squame; nearly equals length 
of autennal peduncle. The <' finger'' and 'Hhumb^ of small chela end in simple, sharply |>ointod 
hooks. There is an inconspicuous tuft of setse on the dactyle. The carpus is long. (See Table IF.) 

No. 8 is also an interesting variation. The antenna) 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 to 12, in the middle of the table, 
show in one way or another intermediate characters between the extremes, Nos. 1 to 4 and Nos. 
13 to 15. 

VI.— MSASUBEMENTS IN MIIXIMETEBS. 



Table n. 

[Locality t Nauao. N. P., Bahama Islands.] 



Habitat 

Sex 

Number in Table I 

Length (tip of rostnun to end of teUon) 

Length of carapax, inclading rostrum 

Greatest width of carapax « 

Greatest depth of body 

Distance between ocnlar spines 

Breadth of second abdominal somite 

Depth of abdomen (with ova) 

Length of terga of abdominal somites in median 
line : 

First tergnm 

Second « 

Third 

Fourth 

Fifth 

Sixth 

Length of telson 

Brecuith of telson at base 

Breadth of telson at tip 

Length of antennular stalk 

Length of antennular segments : 

I'irst • 

Second 

Third 

Breadth of first antennular segment , 

Length of antennular or aural spine 

Width of same at base 

Length of exopoditeof antennule 

Length of endopodite of antennule 

Length of antennal stalk 

Length of long segment of same 

Greatest width of long segment 

Length of squamous spine 

Length of "s<iuame" 

Width of spine and scale at base 

Length of inferior basal spine 

Length of superior basal spur 

Width of basal segment 

Length of same to articulation of squamous spine 
Length of flagellum • 



Green 
»po&ge. 



42 
15 
11 
11 
2. 
15 
15 



2 

6.2 

5.1 

4.1 

4 

3.8 

5.5 

4 

2 

6 

3 
2 

1 

LI 

4 

1 

6 

9 

6.5 

"4.6 



L2 
4.7 
5 

L9 
2.2 
0.3 
LI 
2.0 
16 



Green 
sponge. 



29.7 
11 



L7 



L3 

2.8 

3 

3.3 

2.6 

2.6 

4 

3.2* 

2 

5.2 

2.2 

2 

I 

1 

3.7 



7 
10 
5.5 
4.7 
LO 
4 
4 

1.7 
2 
0.2 



15 



Rocks 

DixlH. 

Keef. 



16 
7 
4 

4 



0.9 



L6 



L4 

"6.'9 



Rooks: 

Green Key 

Reef. 



9.5 



L8 
0.9 



0.7 



2 
3 
L5 



1 

"o.'s' 



3+ 



Rocks 

Gn^n Key 

Reef. 



10.4 
4.4 
2.3 
3 



L8 



0.7 



L5 



L2 

0.1 



0.7 



Brown 
sponge. 



11 
4.5 
2.1 



L9 

1 



0.7 



L8 
2.7 
L5 



0.9 

'o.'s" 



5.8 



Rooks: 

DiiPt. 

Reef. 



21 

8 
5 



3.3 
2 



2.3 



2.8 



2.1 

1.9 




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387 



Table ii— Continued. 

[Locality : NaBaiui, N. P., Babanu Islands.) 



JBAbltot 


Green 
sponge. 

9 
2 


Green 
sponge. 

d 

1 


Rocks: 

Dix Ft. 

Reef. 

9 


Rocks: 

Green Key 

Reef. 

d 


Rooks: 

Green Key 

Reef. 


Brown 
sponge. 


Rocks: 

DixPt 

Reef. 


Sex 


9 


9 


9 




Namber in Table I 




P 











Length of propodus of large chela 


15 
11 

5.5 

4 

4.6 

5.2 

4 

3 

2.8 

5.5 

3 

6.7 

4 

2.4 

1.8 

3 

1 

2.3 

6 

2.7 

7 

4 

1 

2 - 
2.2 
5.1 
5 

2.8 

6.2 

6 

1.2 

8 

2 

,5.8 

4.2 

5 

3.5 


16 
11 

6.1 

4.6 

5 

6.5 

6 

3 

2.4 

5.3 

2.6 

6 

.3.1 

2 


"*5."i' 


5.7 
4.4 
2.5 


4.5 
3.4 
2 
L4 


6 

4.4 
2.4 
2 


7.7 

"3" 
2 


Length of aarae to spine at base of dactyle 

Greatest width of sarae ..-. . 


Greatest depth of same -. 


Width of same at spine, at base of dactyle 

Length of " thnuib " of propodas 




2 








Length of dactyle 


2 

1 

3 

1.7 

2.2 

l.H 

0.9 


2 

1 

0.8 
2.5 


1 


2 - 




Width of same, over tooth 




Length of carpus of large cheliped, on upper me- 
dian line. . .- -- ..---- 


0.6 
2.0 






Length of roeros of same 


2.0 

1.5 

2 

1.3 

1 




Greatest width of meros of same 


Length of propodus of small cheliped....... ...... 


2 

1.8 
0.8 


4.5 

3.4 

2 

1.4 

1 


Length of Qiime to articulation of dactyle 


Greatest width of same 


Greatest depth of same 


Length of dactyle of same 


3 

0.9 

2 

5 

2.5 

5.5 


1 








Width of dactyle of same 








Length of carpus of same ............... 


1.9 
3 

0.8 


1.5 


0.6 
2 


1 

2 




Length of meros of same . ........ 


Greatest width of meros of same 




Length of carpus of second pereiopod 


1.8 
0.8 
0.6 


1.7 


1.7 




Length of first segment of carpus of same 

Length of fifth segment of carpus of same 

Length of second, third, and fourth segments of 
oarpnsof same. ....-- 






















T^nirth of nroDodus of same ............... 


2 




1 


1 


1 


.i.... 


Length of meros of same 


Length of propodus of third pereiopod 


4.6 
2.7 
5.8 
1.9 
1.5 
3 5 












Length of carpus of same 












Length of meros of same . ...... ...... 












Length of protopodite of third pleopod ... 












Width of same 












Lensrth of endonodite of same. ............... 












Greatest bread tn of endopodite of same 


1.6 

4 

3.7 

3.7 

2.9 












Length of exopodite of uropod, 

Breadth of same 






















Length of endopodite of nropod 












Breadth of same 








..-.t. 


















Vn.— THE CAUSES AND SIGNIFICANCE OP VARIATION IN ALPHEUS SAULCYI. 

If we consider Nos. 1 or 2 of Table 1 as representing the nearest approach to the mean of the 
species, Nos. 5 to 15 must stand for individuals which have liuctuated 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 1 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 
sx>ecies and becoming different at different periods of its life, or do individuals deviate from the 
mean of the species, each along its own line f Further, are the variations congenital ! While we 



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388 MBMOIBS OF THE NATIONAL ACADEMY OF SCIENCES. 

are uot prepared to answer these questions as fally as we coald wish, yet the facts are safficient 
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 larveB of these i>rawns 
the external antennae have a well developed scale, and it is thus clear that this organ may degenerate 
and apparently disappear, to be reconstructed again at a later period. The variety longicarpus (No. 
15, Table I) has no " squame,'' although it is present in the young (Fig. 7, PI. xxii), and the cases in 
which the organ is seen in various stages of development (Figs. 13, 14, PI. xxii) supi>ort and illus- 
trate this conclusion. This, however, is not a rule with the si>eci6S 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 larvaB 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 exiieri- 
ments remain to be performed. The evidence we have goes to show that the young in any given 
case share the pecnliarities 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 illustrate 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 larvse 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 setsB on the dactyle. In the first larva the 
fingers of the small chela also end in prongs, and there is a tuft of rudimentary setie on the dac- 
tyle. In the adult the carpus of the small chelipcd is relatively very long. In the first larva the 
carpus of this appendage is about one-third the length of the proi)odus (relatively a little shorter 
than in the adult). Fig. 11, PI. xxn, may be taken to represent the mother (rostrum here wanting), 
and Fig. 1 7 the young. The small chela of the mother is shown in Fig. 2, PI. xxiy, that of the young 
in Fig. 15, PL xxn. 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) (PI. IV, Figs. 1, 2). The larvje are shown in PI. xxi, 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, PI. XXII). 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, PI. X3:ii). 

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 interesting 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, bnt 
aberrant males are probably the more common. 

The occurrence 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. 

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 it« environment and its young resemble 



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MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES. 389 

it. Has nataral 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. 



Paet Sboond. 
the development of alpheus. 

I. 8TRUCTURB OF THK LARVA. 

(PI. XLix, Fig. 174. PI. Lin, Fig. 196. Pis. liv-lvii.) 

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 gei^eral survey of the anatomy of the first larva of Alpheus saulcyi. A fuller 
description of the histology and histogenesis of the tissues will be given in tile parts which treat 
of the different organs in detail. 

A profile view of the larva as it appears while still inclosed by the eggshell and of one imme- 
diately after hatching is seen in PI. xxi, Figs. 1 and 6, 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 (Pis. xxi-xxrv). 

Most noteworthy are the large, stalked, compound eyes, the segmented abdomen provided 
with its full number of appendages, the short, stumpy antennae, and tlie swollen chelae 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 rudimentary pleopods, the unabsorbed 
food 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 Pig. 196 (PI. LUi) the plane of section is nearly vertical and median throughout, except 
for the posterior half of the abdomen. The supra-cesophageal ganglion, which is usually spoken of as 
^Hhe brain'' («.o.^.), is a complex organ, composed of internal, medullary masses {punJctsubstanz balls), 
and cellular tissue which completely invests them. It is made up of the fused ganglia of at lease 
two segments, those of the first and second antennse. This fusion is complete from the early stages 
of development, and the relations of the parls are now extremely complex. They are best illus- 
trated by a comparison of the series of transverse sections (Pis. Liv, LV, Figs. 211-219) with 
those made in a horizontal plane (PI. lvti. 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 which it has nothing to do. It is essentially Skfelt 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 (PI. LV, Figs. 212-216), are the 
largest. They are completely fused on the middle line and form a single compact mass, which is 
slightly constricted laterally (PI. lvii. Fig. 242, of.) and which is divided in front (PL liv, Figs. 
210, 211), where it gives off two diverging stems of fibrous tissue (sometimes called optio nerves) to 
the optic ganglia in the stalks of the compound eyes (see also PI. lvii. Fig. 240 of.). 



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390 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES- 

Next in point of size are a pair of large lateral balls^ which appear kidney-shaped in transverse 
section (PI. lv, Fig. 216, If.). Each is virtually segmente<l at the lower snrface into two lobes (PL 
L.VII, Fig. 242, If.). 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 fibrons masses 
(PL LV, Figs. 215, 21G, af.) fuse with the anterior mass at the same iK)int Each of these balls 
is also bilobed, and from them issue the fibers of the antennnlar nerves. (PL Lvn, Fig. 243, n. 
an., also PL LV, Figs. 212-214, a. o., nau.) The nerve of the first pair of autennie consists of 
ci^Us and fibers, which pass to a mass of deeply staining cells (a. o.), the ear^ and to the tissneaof 
the antennular stalk. The fourth pair of fibrons masses (PL lv. Figs. 217, 218, gf.^ also PL lvtt. 
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 tissuej^ of the appendage (Fig. 216, n. ag.). From this 
same region (Fig. 2I8,/o.) the commissures which surround the cpsophagus and unite the brain to 
the ventral nerve cord also originate (Fig. 220). These commissural bands meet immediately 
behind and below the cesophagus, where they fuse (PL lv, Figs. 222, ocm.) 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 np 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 double chain. These relations are well 
shown in Fig. 196 and by the horizontal section (PL lvii, Fig. 243). The first six thoracic ganglia 
are very closely crowded together (Fig. 196, g. 4-9) and form wliat is usually known as the 
infra cesopluigeal ganglion (ganglia of mandibles, first and second maxiihe, 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 segment*^. 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 markeil (Fig. 196, g. 15-20; see also the series of trans- 
verse sections, Pis. 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 (PL Lni, Fig. 198, gf.). 

The optic stalks or lobes, bearing the compound eyes (PL liv, Figs. 209, 210, and PL lvti, 
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 fibrons 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. 
Thei^e is a nanplius eye (PL liii. Fig. 197; PL liv, Figs. 209, 210, oc.) borne on a median papilla, 
which projects downward between th^ 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 oesophagus, 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 (PL Liu, Fig. 196) and series of transverse and horizontal 
sections (Pis. lv-lvu) illustrate the structures in more detail. 

It is interesting at this poin^^ compare the larva shown in Fig. 196 with the longitudinal 
section of an advanced embryo (PL xr^viii, Fig. 1 68). In both we recognize the foregut, a tube bent 
on itself, consisting of the oesophagus and masticatory stomach (tw. /?.). 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 



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MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 391 

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

The oesophagus (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 oesophagus the sbape of the letter X when seen in transverse 
section (PI. lvii, Figs. 241, 242). Th'e walls of the masticatory stomach resemble those of the 
CBSophagus, and the folds of the latter are continuous with the valvular structures of this region. 
The lateral and median thickenings (PI. 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 (Fig. 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 
(Pis. LV-Lvn). It consists of seven parts or divisions: a dorsal, unpaired, median division (mg, 
in all the figures), and, opening from this, a pair of anterior lobes (w^.^), 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 moat pronouiiced. 
Correlated with this distinction is the fact that the foregut is a blind sac and completely cut off 
from communication with the yolk until very late in embryonic life (PI. XLViii, Fig. 168). The 
anterior lobes contain the remnant of unabsorbed yolk (Figs. 218, 237, ^.), and in cases where the 
lining epithelium 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 
roesodermic core. The ventral and lateral walls of these diverticula are devoitl 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 PI li, Fig. 186, mg.^). They lie to one side 
of and below the hindgut (PI. lvi, Figs. 226-230, mg^.j 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 
bom 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 (^^.'). 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 ventrolateral 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 caeca. One pair, corresponding 
to the posterior division of the midgut (Fig. 226, mg.^), is imperfectly divided into three lobules, 
as in the early larva. They ext>end backward, below and to one side of the gut. The two remaining 

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]iiMr» pi%m Tut ward oq either side of the luaHticatory stomach to a |>oint al)out on a level with the 
Jii8t iniixillmy segment. The ventral is the larger and longer of these, and two lobules are oon- 
fttrictiHl ott from it near its extremity. They correspond to the ventral lobes of the midgut (m^.* 
ent, Fig* 2). The dorsal pair represent the anterior lobes Img.^)^ which are now entirely withdrawn 
froin tlie heiMl region, and naturally contain no foml yolk. The gastric cu^ca are all tilled with a 
coa^itlable tlutd which stains feebly in carmine. The gastric*epit helium for a short distance behind 
tlje point wheii) glands communicate with the stomach has marked histological iHMmliarities. The 
iutenial absoi bent surface is increased by folds which nearly obscure the lum(*n of the tube. The 
vvWh are caliiLtinar and resemble the glandular cells of the liver and probably have the same origin 
us the latter. In the masticatory stomach there is a strainer of hairs developed on the ventral 
and Literal walls which are greatly thickened, as we saw in the larva. The dorsal wall is thin, 
but there 18 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 
llieir di^tribtuion by means of sections alone. The heart (PI. Liii, Fig, 19G, U.) is a short tubular 
olmmber, tlattened between the dorsal body wall and the enlarged section of the hind gut. It is 
Kiispended in the pericardial sinus (p. s.) to the body wall and surrounding organs by means of 
Htraiid^ of coiiaective tissue (alae-cordis). The walls of the heart are quite thin, and its cavity is 
i>artia1ly divided into three compartments by the growth downward from its roof of two sheets of 
mesoderm cells (PI. LVi, Fig. 231, and PI. Li, Pig. 180). 

Of the several arteries which lead from the heart, three, and possibly five, can be distinguished. 
Posteriorly the heart is continuous with the large niiperior abdominal artery, which traverses the 
ubtlomeu clo^e to the dorsal wall of the intestine (Figs. 100, 232, 235, a. «. 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 oi'pr.) is given off, and passes directly downward to the ventral nervous system, which it 
penetratef^ 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. t. a.) Anteri- 
orly the bejirt gives off the unpaired ophthalmic artery (Figs, 196, 216-229, op, a. op.\ which runs for- 
wartl to the region of the eyes and brain. It is not an o))htlialmic artery, strictly speaking, but from 
the first, supplies arterial blood to the brain and anterior cephalic region generally. In Figs. 215, 
216, it i.s seen cut in partial longitudinal section, where it evidently communicates with the blood 
spii.ce surrounding this part of the brain. The autenual arteries can not be clearly distinguished 
In secLioiif^, bub in a much earlier stage trains of cells are seen at the surface of the egg passing 
forward on either side of the middle line toward the eye stalks, which possibly represent the anten- 
iial vi^ssels. 

Besides the sinuses already mentioned, there is a large sternal sinus (Fig. 196, sis. «.). This 
occupies the i>xtensive space between the thoracic ganglia and the alimentary tract and "liver,'' 
uii«1, like all other similar spaces, is more or less completely filled with serum and blood corpuscles. 

Five pciirs of gills are present at this stage. They are developed from simi)le pouches or folds 
of the skill on the bases of the thoracic appendages (Figs. 193, 230-2;^{, br ^ ^). The outer sur- 
fiice of this primary fold soon becomes divide<i into a number of secondary folds or gill plates, and 
iu a larva which has moulted twice and is twenty-four hours old, the brancbia has the structure 
shown iu 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 
Urancbioiitei^ites (Fig. 193, hg.) probably serve as important respiratory organs. 

In respect to its muscular system the first larva appears to dififer but little from the adult. 
The rtexor and extensor muscles of the abdomen are most prominent ( Fig. 190, wfw./., wm. c). The 
former cou.Hi.sts of a double rope of ^ers, fuse 1 completely together and very much twisted. Tliey 
exteiMl from the sides of the thorax to the terminal telson (Fig. 227-235. wtr./.). The extensor 
muscles {nm, 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 iu 
Figs. 227, 228. 

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



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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 393 

over the nervous system (Fig. 221, ad. m.). Closely associated with it are the muscles of the 
roaxillse. The large flat tendon to which the adductor muscle of the forceps is attached, is well 
developed at the time of hatching. It is 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 of the cells of this infolded sheet now oppose each other and secrete the chitinoua 
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 ectobla^t and mesoblast at 
these points. 

The green gland (PL lui. 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 sa6s 
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 lowjer end, and to the outer wall is applied the 
solid nodular bo<ly. 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 oesophagus and passes down to the labrnm and into the eyestalks. The solid almon<l 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 ot 
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, E. O.). 

With this sketch of the structure of the larva we are ready to trace the history 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. 

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

(a) Alpheus. — The ovaries of Alpheus are paired cylindrical bodies which extend between the 
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, siccording to the 
color of the egg (PI. rv). The oviducts open in the usual way by means of a slit-like valve on the 
basal joint of the third pereiopods. 

In PI. 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 art? ready to leave the shell, and the new ova are laid in a few hours 
after the hatching of the larval br6od. Thus there is a constant succession of young, and females 
are not commonly found without either attached or large ovarian eggs. The breeding se^ison 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- 
minal epithelium. The external layer of the sac (O. W.) is muscular and contains numerous nuclei. 
Between the epithelium and fibrdus coat there is a wide space filled with blood. This niay be 
unnaturally large 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 frwofold: (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 begm to develop, ^ 

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while the ovarian lobe is yet crowded with ri|>e 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 epitheliam increase in size along a certain tract. The cells grow rapidly and are slowly 
dehisced or pressed into the cavity of the sac. Each 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 a 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^j every stage can be 
traced. The yolk appears very early as a fine granular dejwsit in the protoplasm of the cell. 

In this species the development is nearly direct, there being no zot*al stage, and the egg 
contains more than nine times as much yolk as the egg of Alpheus minus j in which the first larva 
is a zoea>like form. The materials for the yolk must be derived directly from the bloody 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 reentrant blood sinuses which penetrate all parts of the ovarian stroma, as in 
the lobster (Homartis) 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. II, G. V.) is filled with coarse chromatin grains, and in the early 
phases grows relatively faster than the rest of the egg. In the egg, (e,' to the left) which is xk(j inch 
in diameter, the diameter of the germinal vesicle is one-hajf that of the entire egg. 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 crowd«Hl 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 fused 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 rii>e * 
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. 

(h) 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 syncytium and consists of a matrix in which great numbers of small nuclei are 
embedded. These nuclei, with surrounding protoplasm, give rise (I) to ova and (2) to cells of the 
egg follicle. 

The growth of the ovarian egg from the epithelial nucleus is illustrated in PI. xxv. Figs. 3, 6. 
Fig. 6 is from a section through the posterior end of an ovarian lobe of a lobster obtained from the 
Baltimore njarkets 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. G, 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 (Bl. S.). The sinuses are definite reentrant channels with thin membranous walls. 

The ovarian tissue (Ct. »S.) consists of a fibrous matrix in wliich 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, O^) swells out, becomes spherical, and its chromatin has the chaMWSr T 

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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. Tbis layer 
represents primarily the cell protoplasm, in which the yolk is formed. The cell takes on a doflnite 
shape and is very early invested with a follicular coat (F. 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 (F. C). The growing eggs pass out 
from the central to the peripheral parts of the lobe in 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 germiftal 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 



* Since the above accoant was written I have been able to study the stmcture of the ovary more thorongbly, 
and the subjoined notes We largely extracted from a preliminary notice on ''The Reproductive Organs and Early 
Stages of Deyelopment of the American Lobster." (23.) 

The structure of the mature ovary is somewhat peculiar. The free, unextrnded eggs fill the lumen 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 immature ova. 
The glands are in close relation with the growing eggs. They are plaited or folded structures, and consist of a single 
layer of oolnmnar 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 t^ 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 cieca have much thicker walls; the rapidly dividing cells 
are smaller, 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 caecum 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, in 
which very young eggs occur. Degenerating cells occnr not only in the stroma, but probably in the developing ova 
also. In Peripatus Nova Zealandiw 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 olapsed after egg-laying (eggs in egg-nauplius stage), the gland-like bodies 
have almost wholly disappeared. The walls of the Cfeca 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 
rf 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 abont to hatch, the condition is similar to the last. 
It is now about eleven months since the eggs were laid, yet the diameter of the largest ovarian ova is only about oup- 
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 have 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 
organs are recovering from the changes which follow tbis 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 
handy might lead us to suspect that they were more or less rudimentary structures, or that they were concerne<l with 
the secretion of the gluey substance with which the eggs are eoated 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 recently 
monlted 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 egg, which wo 
have traced from the summer when eggs were laid to the following summer wheu these eggs were hatched, is very 
noteworthy, and shows conclusively that the lobster is not an annual breeder. 

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396 MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES. 

ill each egg is very small, although the number of eggs produced by this auimai is euormous. At 
Nassau, Palinurns begius to spawn in June. 

(d) Comparison.— IshikawB, describes very fully the ovaries and ovigenesis of the prawn At- 
yephyra compressa and concludes that the ovum "originates from the inner lining of the ovary and 
is at the beginning a cell with a nucleus and one, two, or rarely three nucleoli.' The mature eggj 
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 oviducts of Atyephyra possibly secrete 
the viscid fluid by which the eggs are attached to the swimmerets, yet this point needs oomfir- 
mation. 

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

Das Eierstooksei von Pa^cnrus ist in der ersten Zeit seines Beetehens eine eohte Zelle mit Protoplasoia, Kern and 
Kern-Korperchen. Spiiter fiufdet eine Einlagorung von Deutoplasma and die Bildung einer HUlle aos Chitin statt. 
Eudlich wird der Kern ansichtbar ; das Ei stcllt dann eine Cytode vor. ' 

Das fertige Ei verlusst den Leib dos Krebses ohne Kern nnd mit einer IlUUe yersehen. 

This description answers for Alpheus in all essential points. 

The ripe egg of the crayfish (Astdcus fluviatilis) is inclosed by a single envelope, the chorion. 
According to Ludwig aud Waldeyer it is not known whether this is a product of the egg or of the 
follicle cells. Huxley (2C) 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. . 

In Cranyon vulgaris Kiugsley (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. 

Lud wig's general statement that the egg cells of ail Arthropods are surrounded by a vitelline 
membrane (Dotterbaut), the pro<luct 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 Beueden, restricts the terra 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 tbe^ 
winter eggs of Daphnia and Tardigiada, 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 oh M. Clapari^do Ta si nettement d^tinie dans son travail sar . 
les vera Nematodes : C'est la coucbe exteme du protoplasma de Iccuf, qui, ayant acqnis nne density pins grande que 
la masse sous-jaconte, se s^pare de celle-ci par un contour net et trancbd. Elle est h I'oeof ce qne la membrane cellu- 
laire est th la cellule ; elle se forme .de la mdme mani^re. 

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 (Oammarus locusta) agrees quite closely with 
what takes place in Alpheus and Ilomarus.' 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 deutopUism because of secondary origin), which are also suspended in the protoplasm of the 

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 397 

In insects 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 
exi>en8ive 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 (16) describes three egg- 
membranes for the lobster, but it is clear, as Mayer has already shown, that the inner, delicate 
membrane which has been describe^l for the decapod egg^ is a secretion product of the blastoderm. 

ni. 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 (P). xxvi, 
Fig. 14) the nucleus is elongated and about to divide. Division appears to be direct ami 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. S.), 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 consist^, 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 i)resent 
in the stage shown iu Figs. 12, 13. The nuclei vary in size from refringent particles to bodies of 
ordinary nuclear appearance. 

Figs. 25 and 20 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 diflferent 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 (S.) into the clear field. In 
Fig. 22 a small protoplasmic area occurs, iu 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 isee 
structures similar to the cell 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 vi of 
A. saulcyi^ at the period just before invagination, but it is quite unlike anything which I have seen 
iu 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 described in 
another section, and from a cytological point of view it deserves careful study. 



* In singlo sections the nncleoH is strictly central, but whether it is so with respect to the entire eg>r it is not easy 
to determine. Minot states that the egg uocleus is always eccentric. — Aui, Xaturaliet, Vol. xxiii, 1889. 

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MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 



nr. — THE DEV^LOPMBNT OP THE EMBRYO. 

Stage I Segmentation to formation of the blastoderm. 

These observatious relate to Alpheus het^frochelis of the Southern States, to a Bahaman form 
Ti'hich hatches as a ^oea bat which otherwise resembles this species very closely, and to Alpheus 
saulcyij also the from Bahamas, which has large eggs and a nearly direct development. Except 
where it is necessary to mention specific difterences, these three species will be treated as one form. 

In June two Alphei {A. mulcifi) laid eggs in an aqanrium, 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 PI. xxvii, Fig. 17. I reganl 
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 
susi>euded in it. The massive yolk is composed of corpuscles of uniform size, excepting at the 
l)eriphery where they are much smaller. Numerous small lacunas 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 subje4*.ted 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 ; it is lenticular in shape, and granular 
in api^earance, 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 karyokinesia 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 eggj 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 i)re8ent, 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 process<»s between the 
surrounding yolk spheres. It is important to notice that the products of the segmentation of the 
first nucl'^us 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 which 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 
oat on all sides into the yolk. We may look upon the yolk pyramid as a cell in the.strict mori)ho- 
logical sense, its protoplasm being concentrated about the nucleus. The blastoderm or primitive 
egg envelope arises through the multiplication and consequent redaction 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 31. 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. 

The segmenting egg of Hippa talpoides is shown in Pig. 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 

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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 Palw- 
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 inclosed central yolk. All the nuclei reach the surface and take part in forming the 
blastoderm, so that alUhe 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 
blastodermic 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. 

SxAaE II. — 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 e^gg 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 ^gg so that a germinal 
area or disk (G. D.) representing the future embryo is formed. The side of the ^gg shown in 
Fig. 47 corresponds to that occupied by the germinal disk. In reverse view there are much fewer 
nuclei. The ^gg 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 (Fig. 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 j 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 ^gg. 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 theip 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 e>gg 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 tbe 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 amoebje, by taking the food directly into the protoplasm of the cell. 

The critical stage at which ce41s begin to pass from the superficial to the central [)arts 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 Qgg^ 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 tbe lobster the primary yolk colls arise by dolaminatlon, and as suggested in Section V, this is possibly true 
of Alpheus. 



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400 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

before all the protoplasm, that is, the nuclei aud periuaclear protoplasm of tlie yolk pyramids, 
has reached the surface. lo the slightly older phase, shown in PI. xxx, Fip^. 46, all the proto- 
plasm which does not pass inward is strictly 8ui)erficial. 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.), api>arently 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 8U{>erticial seg- 
mentation of the yolk is still apparent. We now have a primitive ejnblast, or external layer of 
cells, aud a primitive hypoblast, composed of yolk cells which have migrated from the blastoderm. 

The invagination stage immediately follows that last described (PI. xxxi). 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 downwanl into the yolk. The invagination is nearly solid, and 
the segmentation cavity is still filled with the great mass of yolk and with primitive hy)K)blast. 
In the crayfish {A8t<icus fluviatilis) the invaginate cavity becomes a closetl 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 aud 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 (PI. xxxi). 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 i»o8terior 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. 
51 is a part The pyramidal cells, which form the floor of the depression, contain at their 
peripheral ends no unabsorbeil yolk, but at the deei)er ends of the cell, below the level of the 
nucleus, the cell boundaries are lost, and the ])rotoplasm of the cell blends oft* into the yolk and 
ingulfs its finely divided particles (Pig. 60). Numerous cells (Figs. 52-54, b, b**) have alre^ly 
wandered from the point of invagination into the egg and a considerable distiwce forward under 
'the germinal disk (Fig. 54, G. D.). These cells are more or less intimately unite<l by pseudoi>odal 
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, (i. D.) is still one cell 
thick. At the close of the invagination stage the primitive hypoblast has received a consid- 
erable accsssion 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 primifive 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 coelenterate plauula 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 anj- 
sense general or typical. 

Stage III.— Optic disks and ventral plate formed. 

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



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MEMOIRS OF 1;HB Is'ATIONAL 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 a lateral band or cord 
of cells (L. Cd.), on which the ai>peudages 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 nuclei. 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 optic disks to 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 
pells. 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 vmultiplying 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. ix, Figs. 61, 63) tend to form a syn- 
cytium, 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 eggy 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 stddn with much less intensity than the 
superficial epiblast. This shows that they are multiplying rapidly, and the finely divided yolk in 
their neighborhooil shows also that the cell protoplasm is rapidly absorbing food. A series of trans- 
verse sections of this embryo is given in PI. xxxiii. 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 iK)lygonal, 
cell boundaries are distinct, 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 IV. — Thickening of the optic disks and rudiments op the appendages. 

An embryo a few hours older than the last described is shown in Fig. 72. On the thickened 
cords of cells (L. Cd.) uniting the optic disks to the ventral x)late the traces of two pairs of append- 
ages can be made out— the first pair of antenna 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. 94 26 



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402 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 

several Important changes siuoe the last stage. The ventral plate is more extensive and the 
wandering cells are more nnmerous. The primary and secondary wandering cells can no longer be 
distinguished, bat 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 l^st 
stage (Fig. 59.). The transverse cord (T. Cd.) is seen to consist of a single layer of flat epiblastic 
ciells. 

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 lu (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 ; that is, to delamination and emigration. (Compare cells ECf, EC'^, 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 segmeAt. 

Stage V.— Rudiments of thbee paibs op appendages — cell degeneration. 

The embryo represented in Fig.* 93 is, approximately, three days old (temperature at Nassau 
78-800 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 equifateral 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 
aud the kniddle of the opposite side would therefore correspond with the longitudinal median 
axis of the embryo. 

The rudiments of the second pair of antennse, 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 
antennae and the mandibles. All are developed nearly simultianeously, but the second pair of 
antenme 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 (G. M.) are areas of rapid cell division, and are characterized by the presence 
of large granular nuclei 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 antennae 
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 



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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 
outlfnes 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, Be), but elements closely associated with yolk are usually amoe- 
boid, the nucleufe 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 angnlar 
in consequence of crowding, and deep-lying nuclei are generally spherical. 

The arrangement of the embryonic cells of the 8U[)erficial epiblast in beautiful curves and rings 
around definite centers — orthogonic systems of curves — is not nearly so pronounced as in the embryo 
crayfish {Astacun Jiuviatilis)^ according to the delineations of Keichenbach and Winter. Beichen- 
bach states that in the crayfish the superficial embryonic cells multiply about a given center, like 
that of the "head fold" (optic disk), or *Hhoracic abdominal rudiment," according to definite 
laws. This was discovered by Sachs in the growing tips of plants. According to Sachs, Keich- 
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 givipg 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, and the different cell groups soon in^pinge 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. xxxvi. Figs. 88-90), and is 
about seventy hours old. It is from the same prawn as the segmented egg shown in PI. xxvii, Fig. 
15. These sections give som^ 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. 0.) is nearly in contact witl\ the 
superficjal 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 out^r surface of embryo ; another (Y. O.*) is in a distant 
part of the egg and is in the aster stage of karyokinesis ; others still (Y. G.^) 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, Be. dotted line extended) has just passed below it. 

Figs. %(S 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. C.^) 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 thQ 
thoracic-abdominal 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 

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MEMOIB8 OF THE NATIONAL ACADEMY OF SOIENOBS. 



apon the optic disks, the bases of the appendaj^es, and other parts of the embryo. They also 
pass to the extra-embryonic surface of the e^|?. In Fig. 91 one of these wandering cells (T. 0.) 
is approaching the surface, while another (Y. C) nearly touches it; and in PI. xxix, Fig. 34, 
which represents a portion of a section from a later series (Fig. 106) greatly enlarged, we find 
two yolk elements (Y. G.) 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 epiblastic 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 th^ nucleus is flattened against it and the ordinary epiblastic cell, 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 (Pigs. 96, 97). The optic disk, which in stage iir 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, 
C. M., O. J>., is clearly difierentiated. 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 (0c.) wh^se nucleus has sunk below the level of the surrounding cells, 
but the cell protoplasm still reaches up to the surface. Such cases render one cautions 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 delamiuating. Cases of this kind were rarely noticed, but were observed at 
a later stage (PI. xxxix. Fig. 102, ec). That wandering cells attach themselves to the optic disk, 
ther«i 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. O.) until they finally come in contact with-it 

The thickening of the optic disk described in Stage in ( PI. xxxiii, 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 vi. 

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 stomodsBum (Fig. 98, 
Std.) is just making its appearance as a slight invagination of epiblast on the middle line between 
the first pair of antennae. 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. 



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MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 405 

In Fig. 98 several independent cbromatin balls (S) are seen in the yolk, and the granular 
cells of the ventral plate are very marked. A large nuclens 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 (Ec.') 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 stauds 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 case 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 ecjo-nauplius. 

The fully developed egg-nauplius is represented in Fig. Ill, but before this condition is reached 
there are several intermediate stages to be considered. A series of longitudinal sections (PI. 
xxxix, 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 stomodsBum (Fig. 105, Std.) has the form of a straight, narrow tube, between the buds of the 
first and second pairs of antenuaB. 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 
a simple 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 stomodaeum is a relatively long straight tube with very slight lumen, and is surrounded 
with chromatin grains and scattered cells. It is formed at a considerable distance in front of the 
point of invagination, and one to two days earlier than the proctodeum. 

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 disc (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. 1 have seen nuclear 
figures at the yolk segmentation sta<(e of Crangon, also in Hippa^ Pontonia and Homarus^ and Kei- 
chenbach found them in abundance in Aatacus. Indirect cell division is undoubtedly, the rule in 



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406 MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES. 

the developing eggs of the Crastacea aud probably of all the Metazoa. Since we often stady 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 stomodteum now lies next the egg shell, but soon 
changes its position (Fig. 125, St. A.), owing to the forwartl growth of the thoracic-abdominal fold. 
The labrum, here undeveloped, soon grows backward toward the latter, helping to bend the 
QBsophugeal tube and probably slightly altering the position of the month (Fig. 125). 

The proctodseum 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 
Figs. 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 snr> 
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, amoeboid 
cell to the flattened mesoblast cell, lying close to the surface, can be best followed at this stage. 

The fully developed eggnauplius (Fig. Ill) is about a week old. Embryos from the same 
prawn YSkvy 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. 
Ill 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 determined from Fig. 127, where the plane 
of section is through the long axis of the eggj 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 tbis period the long axis of the embryo (using this 
term ta 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 
may 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 antenme, 
and represent a large part of the future brain. The appendages are all simple, but a bud soon 
grows out from the i>osterior sides of the second pair of antennae 

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 antennae are developed in close union with the ganglia of the antennnles. 
Together they form the supra-cesophageal ganglion or '* brain." The stomodn^um (Std.) appears 
from the surface as a distinct mass of c^'ills 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 maxillse, 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 eggj 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 egg- 
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. C.^) are settling down on the ventral nervous 



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MEMOIRS OP 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 oesophagus, 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. S. C.) 
are seen near the oesophagus, and amoebiform 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. XLT, Figs. 114, 115) traverse the optic lobes, and the 
thinl cuts the brain. The central mass of large cells which was noticed in the optic disks can no 
longer lie distinguished. The lobe (O. L.) is composed of similar cells with granular nuclei, th6 
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, S. O. Q.). 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 (PI. xlii, M. F.). The three following sections 
(Figs. 117-119) pass through the oesophagus, and the ventral nerve thickening immediately behind it. 

About the oesophagus (^ig. 117, Std.) numerous chromatin balls (S., S. 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 si<le of the oesophagus 
the yolk has undergone important physical and^emical changes. The yolk spheres or blocks 
are full of vacuoles and have a corroded and granular appeai-anoe, 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 hsematoxylin and represent the last stages in the degeneration 
of chromatin. The eroded and altered yolk (A. Y. S.) is represented in many of the sections. 
Between the oesophagus and bases of the antennae the yolk is absorbed, leaving a protoplasmic 
reticulum (Fig. 117, Ret). 

In Fig. lis the mass of cells representing the mandibular ganglion (Md. 6.) 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 maxillse (Mx. I.) are united by the primitive layer of epiblaat. 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. 120-123. 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 ceils (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 thoraeic-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 

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408 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 

oaclei have the nsaal characteristics — irregular shape ami granalar coDtents. They are sur- 
rounded by a small irregular body of protoplasm which doe>s not readily stain and which is oftmi 
difficult to observe. In PI. xxix^ 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 sach connection between them. 

The endoderm, though not represente<l 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. 

Stagb VII.— Rudiments op sevrn pairs op appendages. 

Fig. 110 represents a phase intermediate between the egg-uanplius (Fig. Ill) 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 PI. xliv, and Figs. 136, 137, 144, 145. 
Fig. 137, which represents a section just behind the base of the first antennse (A. I.), may be com- 
pared with Fig. 117. Numerous yolk elements are found in the vicinity of tbe a^sophagus, where, 
as will be seen (Fig. 134, Mu.), they become speedily converted ii^fo muscle cells and somatic meso- 
blast. In Fig. 136 several wandering cells attached to the boily wall, have all the characteristics 
of blood corpuscles, a deep staining granular nucleus, and a clear irregular cell body. The blood 
ceil and muscle cell are both derived from wandering mesoblastic 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, PI. xliv. Figs. Ill, 109, 110, and 130 
form a consecutive series of embryos, each but a few hours older than the preceding. In the first 
(Fig. Ill) the optic lobes, first and second pair of autenufle, 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 antenna) 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 antenuse 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 antennae hairs are developed, although 
there is not perhaps so marked a contrast between the first and second antennsB in this respect as 
would appear from the figure. The fiirst and second maxillae 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 sphericul to the lens-shai>ed, 8pindle-8haped,and wedge-shaped forms. Generally all the nuclei 
agree in containing cos^rse 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. 



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MEMOIRS OF THE NATIONAL ACADEMY O^ SCIENCES. 409 

Wandering cells are aow 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. 

Fig. 131 is a median longitu(^inal 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 4ne (Fig. 126) of 
the preceding stage the most striking difterence 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. E.) 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- 
Si>onding 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, 132-136) with corresponding sections of 
the previous stage (Figs. 116, 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. 13^, Mes.) and bear a 
resemblance to muscle or connective tissue cells. They originate from the cells marked Ct. S. in 
Fig. 116, and come from the yolk. Like the cells already mentioned 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 not present until a considerably later stage, they are probably transitory. 
Fig. 134 corresponds closely with Fig. 117. It shows the section of the CBSophagus and of the 
ganglia of the second antennae. 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 oesophagus, is more compact, and its 
cells are somewhat differentiated. The central nuclei are smaller and stain most intensely. The 
oesophagus (Std.) is suspended to the body walls by rudimentary muscles (Mu.), the cells of which 
are much elongated. They are derived from migrating mesoblastic cells like those seen in the 
earlier stage (Fig. 117, S. C), or like the one shown in this figure to the left of the oesophagus. 
Fig. 137, which is from a stage intermediate between the two just considered, gives additional 
evidence of this rdle 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, CQlumnar 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. 136, A. y. S.) is absorbe<l or converted into a granular residue. This layer represents the 
entoblast or the epithelium of the mesenteron already described. Numerous wandering cells are 
encountered (Figs. 124, Mes.5 1^> Y. C), which take up a peripheral position, and from the first are 
closely associated with the epithelium of the hindgut. Th|y unite the mesenteron to the hindgut, 
and it is impossible to say exactly where the one begins and the other ends. Between this ento- 
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 mesobhist (Fig. 



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410 



MEMOIRS OF THE NATIONAL AOADBMT OP SCIENCES. 






w 

t 

% t 



128, Mu.) which extends throughoat the abdomen between the hindgut and body wall. Mesoblaat 
cells derived from the yolk (Fig. 129. Mu.) are also seen nnderneath the epiblast on either side 
of the body. The 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 appeafance of 
blood corpuscles. 

The heart originates m the mesoblast (Fig. 135, if^.), between the entoblast and outer wall 
of the body, jn^t behind the thoracic-abdominal flexure. 

At this time fibrous substance (punktsnbstanz) 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 
autennsd. It is distinctly fibrous and apparently originates from the protoplasm of surrounding cells. 



Stage vm.— Segmentation of the nbbvous system— at least eight 

DAGES PRESENT. 



PAIBS OP APPSN- 



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 tnfle older than the embryo given in PI. XLiv, and can be best 
described by showing in what respects it differs fipm it. 

The rudiment from which the nervous system is formed (Stage vn) 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 vii and ym the 
portion of nervous thickening between the (esophagus, 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- 
nogeu) 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 resuH of this, the thickening of the ectoblastic plate in this region, 
such as we see in the next phase (Fig. 139). 

Kear 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 (PI. XLir, Fig. 120, B. Z.), It corresponds to the budding zone (Knospungszone) which 
Eeichenbach figures and describes in the crayfish. He detects it in a very early stage (Stage B, 
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, l)elow the notch of the telson. From it the segments following the mandibular segment are 
gradually budded oft*. 

Tlie present stage is characterized by the segmentation of the nervous system and 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 in to a double cord. It is, however, discontinuous at the middle of each block, 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 similarly joined to the one behind or 
in front of it. Distinct commissures pass from the brain around the cBSophagus 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 cofitain 
punktsnbstanz. It is developed as a iftnalt isolated mass on the dorsal side of each ganglion, 
toward the middle line. As development jiroceeds these masses increase in size and are grad- 
ually united by transverse commissures in each pair of ganglia (PI. xlvi, Figs. 150, 161, PTc.). 

A mass of fibrons or granular substance appears in each optic lobe in the gangliogen next the 

brain. Fibers pass from it to the punktsubstauz of the brain, which sends .fibers dDwu/to^^Tp 

igi ize y ^ 



liL._^LJ'sb*i;i?. 



MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 411 ' 

oircam-oesophageal commissures to the first post-oral ganglia. The fibroas masses uuite on either 
side of the ventral chain to form a doable 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 Fig. 139. The first post-oral 
segment is the mandibular (g. iv), and following it are the segments of the maxillse 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, which 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, 
containing 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 ci41s also extend down to 
the food yolk, aud 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 hea»t (Fig. 139, H) is now a broad and greatly flattenf d chamber between the body wall 
and endoderm {End), It extends forward a considerable distance between the epiblast and yolk, 
and is continued backward into the superior abdominal artery {A. a. «.). It is filled with serum 
and blood corpuscles. 

The endoderm is a more conspicuous layer (End,)^ and the wandering cells are reduced in num- 
bers, lliey 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. c). 

Stage IX.— Embryo with eye piaMENT fobming. 

A sketch of the embryo at the time when eye pigment has already formed is shown in PI. 
XLYii, 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-f>rown 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 ofiT 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, PI. xxi. Fig. 9.) The plumose setae which garnish the posterior edge of the telson are now 
represented by short stumps. 

The first pair of antenna) are stout, simple appendages, tipped with setse and folded backward 
along the sides of the body. The second pair of antennae 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 Pis. XLVi and XLVii. The drawings are made from different 
embryos, all of which are of the same age, excepting thdfee represented by Figs. 152, 158, 159, and 
161, which are a trifle more advanced. 

In the first series (PI. xxvi, 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 

Digitized by LnOOQ iC 



412 MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES. 

Pig. 146, sbows the complete hiHtory of development of the retinal layer from ita oneoelled con- 
dition toward the median line (already seen at an earlier stage. Fig. 136, Stage vii) to the point 
farthest from the middle line, where pigment is forme<l. The fibrous nerve tissne of the gan- 
liogen now consists of three masses, a ball nearest the brain, which is the first to ap|»ear, and two 
smaller masses between it and .the retinogen. Hnge ganglion cells (gc,) are of frequent occur- 
rence, e8t>ecially at the surface of the eye stalk next the brain. (The details of tlie 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 chiefiy in point 
of size. It is composed of nerve cells and large ganglion cells (gc.)y which occur 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 
U with a wide and short transverse bar. In front of the transverse commissure (Pig. 147, Tc.) 
the fibrous substance is prolonged on either side into the optic lobes; behind, it extends down to 
the ventral nerve conl, on the inner side of the CBsophageal ring (Fig. 148, ocm,). 

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, &). 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, |>r.), 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 cellB and 
correspond to cells similar in shape and origin which appear between the yolk and nervous system 
at a much earlier perio<l (Stage vu. Fig. 131, 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 anteunal segments of 
the brain (Figs. 147, 148) the cells next the yolk are discontinuous. In the circumoBsophageal cords 
the fibrous tissue also is without a cellular cortex on its inner or central side (Fig. 149,/«.). With 
slight changes these relations are maintained in the hatched larva (see PI., ly.. Figs. 220-222). 
The foregut is at this time a tube with definite walls and wide lumen (Figs. 148, I52j fg.). At 
about its middle it is bent abruptly backward on itself in an acute angle. The first portion, lead- 
ing from the mouth to the angle, is the oesophagus 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 (esophagus 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 vii. Fig. 134), where we have already 
seen muscle and connective tissue elements, derived from the wandering cells, extending from 
the (Bsophagus 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 porti^nj^^^e wanderingQ[^ 



MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 413 

cells. This sabject of the rdle of the wandering cells in Alpheas is one of the most difficult and 
a.t 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 vii). 

A new structure, the carapace (Figs. 148-151, 160, cp.), 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 life (V. Fig. 196). 

The hindgut or intestine (Figs. 150, 157, Rg.) has a considerably larger lumen than in the pre- 
ceding stage, but its histology is esseutially the same. The walls are composed of a single tier of 
large cblllmnar 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. 160, 160, mie./.). 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 haemotoxylon. 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 sharp line between them. The 
endoderm cells are vesiculated, have less definite boundaries, and extend pseudopodialike 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 (fl). 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. e,) which migrate 
from the yolk and assume an extreme peripheral i>osition with respect to it. They eventually 
acquire.cell walls, unite and inclose the yolk which they continue to feed upon, api^rently by first 
produciog 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 vii (Figs. 144, 145, Dp.) we noticed an extraordinary migration of wanderiug cells 
to the pole of the egg opposite the embryo. These cells eventually reach the surface and rein- 
forcing the primitive epiblast, give ri8e to a conspicuous dorsal plate, which is shown in Fig. 153 
(Dp.). This is from an embryo intermediate between Stages vni and ix, in which e\ 

Digitized by 



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\ 



I 



414 MEMOIBS OF THE NATIONAL ACADEMY OF SCIENCES. 

is not yet formed. The plate is slightly thicl^eDed at itM center, where there is an iaconspicnoas 
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 numl)ers throngh a large part of the 
ogg* Some of the wandering cells in this region doubtless degenerate before reaching the sarAioe. 
A part of a similar section is shown in more detail in PL y, Fig. 36. The particles vary consider- 
ably in size, stain uniformly and intensely and the yolk about them is granular or linely divideil. 
At a corresponding stage in the lobster (Homarwt americanun)^ I have observed a large diffuse 
patch 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 al>out 90^ behind the 
embryo. This i>osition 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 bye-pigment strongly developed and the posterior lobes 

OP THE GASTRIC GLAND POBMING. 

All the thoracic limbs and the sixth pair of abdominal api>endages 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 seta*, and resembles the larval 
telson, except that the median notch is deeper. 3een from the exterior the eye-pigment has the 
form of an oval disk. 

The longitudinal section, PL XLViii, Fig. 168, shows most of the important changes which have 
occurred since the last stage. These chiefly concern the eye, the nervous*8ystem, and the midgut. 

The ectodermal pigment cells (retinular cells) of the retinogen have spread inward until they 
cover its whole inner convex surface (PI. XLViii, Fig. 167). Near the outer surface of the eye the 
crystalline cone mother cells (cc) can be recognized, and between tbe eye and the ganglia of the optic 
lobe there is a narrow space which communicates freely with the blood sinus {B. S.) on tbe outer side 
of the lobe. Wandering cells are frequently seen rear this bloo<l sinus, and in the -space l>etween 
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 
(PI. XLVii, Fig. 159) the relations of the fibrpus 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 apj)roach in complexity that of the 
larva, which was described in the first section of Part ii of this paper. The lateral fiber-balls, so 
conspicuous in the later stages have now appeared (Fig. 159 and PI. XLix, Fig. 174, I/.). 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 {gf.) which supplies the antennal segment. With this, the oeso- 
phageal commissures are directly continuous (Figs. 171, 174 ocm.). 

The complete chain of ventral ganglia can be seen in Fig. 16S. This section is not i>erfectly 
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 chain 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 crcsc^i*^. A transverse section of the nerve 
cord in the thoracic region is shown in Fig. 172, and corresponds vt^ry 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 the larva.) In the 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 tbe nerve 
cord behind the oesophagus to the endodermal fold (/) 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. 



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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



415 



The two divisioDs of the foregat, oesophagus, and niasticatory stomach, have the relations 
already described. The wall consists of a single layer of tall colnmnar cells. In the masticatory 
division the wall has begun to thicken next the yolk screen, its cells being cuneiform, and the 
nuclei elongated and crowded below the surface. From the anterior wall, muscle or cor^nective 
tissue cells extend forward under the brain. 




^gi * HI 

Fig. 1.— Diagrams of transverse sections through the alimentary tract of an embryo of AlphetiM sauleyi which is 
yearly ready to hatch, to show the origin of tho gastric gland from the postero-lateral lobes of the midi^ut. Section 
1 cats the hiudgut and lobes of the "liver," Section in the hindgut where it merges into the mesenteron. gg\ gg"*. 
Secondary lobules of mp' ; HO, hindgut; m^', postero-lateral lobes of midgut. 

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 iiexure, 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 eaoli 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. 



f . / / 

1^ f J 




Fig. 2.— Semidiagrammatic representation of tho alimentary tract and its appendages in the 
first larva of Alpheiis saulcyi. Tho middle lino of tho body is also shown. FS, foregut ; gg 1-3, 
secondary lobules of postero-lateral lobe of raldgnt; IIS, hindgut; tn^, midgut; mg 1-3, an- 
terior, lateral, and postero-lateral divisions of midgut; ino, mouth. 



Digitized by VnOOQ iC 



41G MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

Wandering cells still occar in all parts of the ^olk, thongh in far less abandanco than in 
earlier stages. We find nnmbers of them moving toward the iieriphery, or next tlit* l»o<ly wall to 
take part in forming the endoderm. The epiblast is conspicuous in Pig. 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 
]>articles which was formerly present in this region. A blood space (Fig. 1G8,) now extends over 
the dorsal side of the ef^g between the epiblast and the yolk, from the heart to the optic lobes and 
region of the head. 

Anteriorly we can distinguish in transverse section three vessels — a median impaired one, 
which answers to the ophthalmic Mtery, 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 snrface of the egg the blood vessels have 
the appearance of two bands of tissue, passing backward from near the |K)iut of union of the 
optic lobes. Between and at either side of the optic lobes, and beneath »nd to each side of the 
brain, we find blood spaces packed with corpuscles (Figs. 100-109, B, S,) 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 (iT.), and is essentially the same as in Stage ix. 

In Fig. 173 there is a small solid cluster of peculiar cells (R. 0.) on either side of thq 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 enve1o[>ed in a capsule of mesoderm cells, like those 
forming the walls of the heart, and they originate from similar elements. In Stage ix (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 uulei^s the 

I sections are uniform and complete it is very easily overlooked. The muscles have developed in 

{ various parts of the body (Figs. 168, 171, 172, wtt., r/iu. /., mu. e., g. m. a.), but most striking at 

[ this stage are the gre^t flexor and extensor muscles of the abdomen. 

J The green gland (Fig. 170, A, O,) is another organ which we now meet with for 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 XI. — Embryo of alpheus heteeochelis nearly ready to hatch. 

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 
heterocheliH 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 convenient 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 (Pis. 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 is 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 screened 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. 

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MEMOIRS OF THE NATIONAL ACADEMY QF 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 present in the peripheral parts of the cavity next the advancing edge of the 
endoderm. Those element43, represented in Fig. 182, prove to be endoderm cells mechanically 
detached from the wall of the mesenterou. 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 Ectoderm p/eiler of Beichenbach, and to these, meso- 
dermal elements become attached. The cavity of the heart is imperfectly divided by lateral 
X)artitions 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 XII.— The first larva. 

We now reach the stage with which this paper began, the first larva of Alpheus sauhryi. 
The histological structure of the zoea in the species with a regular metamorphosis differs only 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 ailH 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. 

Stage XIII. — 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 tlie gills (PI. Liii, 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. 

In a larva four days old (PI. xxi, 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 
ail 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 form. 

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 difl'erentiation 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. 



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t 418 MEMOIRS OP THE NATIONAL ACADEMY OP SCIENCES. 

4 

I The anterior or optic enlargement iH continaoas on each side with the ganglia of the eye stalks. 

^ Its two halves are united by transverse fibers. The lateral enlargement is markedly kidney -shaped, 

^ and from its hilns there issues a complex system of fibers. A great part of these fibers issue from 

I 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 i>ermeated with pyramidal blocks 

\ of a denser substance which stains faintly with carmine. The apices of these pyramids point 

1 toward the center of the ball. Below the lateral enlargement and nearer the middle line there is 

.1 the antennnlar mass fW>m which the auditory nerve issues. This is bilobed and has the same gen- 

1 eral relations as in the first larva (PI. LV, Fig. 216, I/.). 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 05Sophageal commissures. 

^ The alimentary tract has undergone, very important changes, of which mention was made in 

y Section i. W]hat 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 mill, 
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 if«.. 
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 commdh ducts. The 
epithelia of the gastric caeca of the ducts and midgut are directly continuous and pass graduedly 
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 
between the hindgut and mesenterou. But it is certain that only a very small i>ortion 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 csDca. 

The heart is very much compressed from above downward as in the adult. 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 
Decapods, which have been studied chiefly for the sake of comparison with Alpheus. 

Alpheus saulcyi and A. heterochelis are both typical examples of centrolecithal segmentation 
with the formation of yolk pyramids. They possess a massive food yolk and hatch as mysis-like 

* The coucluding sectioDS 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 have failed to eliminate. 



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MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 410 

larvae. On the other hand, the Bahaoian variety of Alpheus Jieterochelis aucl Alpheus minor (from 
Beaufort, North Carolina) agree in having a relatively smaller yolk and in hatching as zoda-like 
forms. They differ, however, in their segmentation, the first species agreeing in this respect with 
A, aatUeyi, 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 
find 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 ^g 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 celln, the blastoderm. More fully stated the process is as 
follows: The segmentation nucleus divides first at a point near the center of the egg. 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 gjradually 
and on one side of the eggj or make their appearance simultaneously in relation to all the nuclei 
present. Segmentation is always rythmical. During one phase (period of " rest '') the segments 
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 ap}>ears 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. C5ell division 
is usually indirect. The only exception to this rule which I have observed is Alphem minor (see 
p. 397). With each division the protoplasm approaches nearer the surface of the eggy and the 
segmenl^s become more pyramidal in shape. These are the "yolk pyramids" which were first 
described in the crayfish by Bathke 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 i)eripheral yolk has nearly disapptored. The greater part 
of the protoplasm of the egg is thus at the extreme outer ends 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 
mesoblast and entoblast. The process above described will be found to apply, I believe, to the 
majority, if not to all Decapods. DiflFerences in detail may be expected in the time of appearance 
of yolk segmentation and the degree to which this is carried. This account diifers 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 hispidiM. — 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 anortier cell, the female pro- 
nucleus, lies near the center. A single polar body was also present, just beneath the shell, near 
the first nucleus. 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 PensBus as figured by Haeckel, but in the latter form yolk segments 

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appear at au earlier phase. The cleavage of the yolk is wholly, or almost wholly, confined to the 
surface farrows, 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 domesHoa^ PaUgmoneteM vulgarisy 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 naclei and corresponding yolk 
pyramids. Here the conditions are precisely like those in Alpheu$ $aulcyi at a similar stage, 
and probably the segmentation of the two is similiar. In Palamonetes Faxon (17), relying 
wholly upon surface views, states that segmentation of the egg begins in two planes almost 
simultaneously. 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 nuclei near the center of the undivided yolk, and a stage 
with thirty-two yolk pyramids. This egg also agrees closely with that of AlpheuM 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^)ell 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 theprotoi>lasm is apparently concen- 
trated in these cells. Yolk pyramids similar in surface views to those of Hippa occur in Callinectes 
hastatt^^ PlatyonychuH ocellatus^ and Libinia catuUieulata. 

Crangon vulgaris. — Kingsley (31) describes the segmentation of Crangon as follows : 

With the first Hegmentation the protoplasm begins to leave its central position and seek tbe surface of the ogg; 
before the second division is completed it has reached the surface, leaving the yolk in tbe center. « * • ^fter 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 firs^ unclear division ; the second is at right angles to 
it. * * * Jn Crangon, so far as I have been able to see, amoBboid 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 occor. 

Of cell division he says: 

In tbe 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 PI. I 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 Ejngsley, 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. I 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, PI. xxvn, of the segmented egg of* 
Alpheus, although belonging to a later phase, will fairly represent the condition of things which 
we find in Crangon. N«ne of the nuclei are tangent to the surface, but between them and the sui - 
face there is still a considerable layer of yolk. Each is surrounded by a large mass of protoplasm, 
which stains lightly with haBmotoxylon, and has the characteristic rayed appearance. One of these 
nuclei 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 Alphens at the same period. As already 
stated, the central yolk mass does not contain a single nucleus. The yolk is in the usual form of 

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MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 421 

large spherales on angular blocks, which are abandantly perforated with round lacnnaB. Crangon 
agrees essentially at this stage with at least three other species, namely, with AVpheas saulcyi^ 
Pontonia domestica, and Stenopua hispidus. 

It is probable that Figs. 3 and 4 of Kingsley's paper do Aot correspond, the latter representing 
the older ef^gj 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 
occurs. 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 AlpJieus sauhyi, 
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 roundabout 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. xxxiii, 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 iuvaginate 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 mediterranean 
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 pentral, and the resulting 
cells, sixteen in number, pass gradually to the surface and form a deep layer of protoplasm 
inclosing the yolk. This la^er, at first raised into hillocks corresi)onding tathe 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 
©gg? 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 occurs. 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 DecaxKxls, are of unequal size and contain nuclei which 
do not take part in the "blastoderm." These nuclei probably corrcvspond 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 Uupagurus 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 saulcyi 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 

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422 MBMOIBB OF THE NATIONAL ACADEMY OF SCIENCES. 

involved. This remark alao appli^ to Stenopofl, where eight blaatomeres or yolk py ramida appear 
at the begiuniug of the third phase. In Homams there is less nniformity in the appearance of the 
8aper6cial segojeuts, since the cells do not migrate to all parts of the Harface at a uniform rate. 

Lereboullet (36) described the early stages of the segmenting egg of the crayfish AHacus 
JluriatUis in 1862. His account, though somewhat vague and unsatisfactory owing to the tech- 
nical difficulties under which he laliorml, 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 Attacus leptodaetylus. 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 segments around them. The cleavage plam^ 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 {^' doiUrkem^ 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 segmeutation 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 Knpagurus. 
Id 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 eel? 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 the 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- 
demiic 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 Sergeste^ 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 occnr in the lobster at the close of segmentation. In each case they arise by ti'ansverse 
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 this was written Professor Brooks bas anuonncecl in bis report of the work of the marine laboratory of 
the Johns Hopkins University, that he has recently obtained the eggB of Lncifer in abandance at Jamaica, and is now 
engaged in studying its embryology. 



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can be said. BrookR thoaght 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 Homarns, on the other hand, the invaginate cells 
unquestionably degenerate.* 

The eggs of ScyUarus 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 jn surface view they resemble, at this time, the ordinary Decapod type. We have as yet no 
knowledge of the segmentation of the Stoinatopods. 

The relations of the difterent varieties of segmentation which are met with among the Deca- 
pods, may be expressed by the following table : 



' (I). Luo^er ijfpus. 



Segmentation of the, 
I)ecapod egg. 



IL Partial : centroleoi- 
tbal (yolk pyramids): 
seffmentation cavity 
L filfed with^olk. 



Segmentation of yolk at first to- 
toly afterwards partial. 



I^Regalai 



(11). 



Segmentation of 
yolk. 



I. Total : regular : seg- 
mentation cavity pres- 
ent. 

(1) Palamon. 

(2) Eupagurua prideauii, 
( (3) Aiyephyra compressa. 

(1) PencdU8. 

(2) Crangon, 

(3) Stenopus hispidua. 
J (4) Alpheus saulcpi, 

' I (5) Pontonia domesHoa. 

(6) Sippa talpoides, 

(7) Palcemonelee tulgari$, 
^ (8) Callianassa mediterranean 
f (1) Homarua americanua (yolk 

segmentation at first ir- 
Irregular^^ regular, but later regular 

or nearly so). 
' ,(2) Alpheus minor. 

Of the Thoracostraca, the Schizopods undoubtedly depart widest from the common decapodal 
type of segmentation. Nusbanm (45) thus describes the process in Mysis Chameleo': 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 zone 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 ceils. " From 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 Fycnoganida which resembles that of the 
Decapod. Here the invagination (which leads to the formation of the stomodaeum) is preceded by 
the delamination of endoderm cells from the blastospbere, very much as in Alpheus, if we may 
regard the yolk cells as primitive endoderm. 

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424 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 

Id AgelcBiM^ Locy (37) foand the onsegmeDted egg to oontain a central nacleas and protoplasm, 
onited by a fine network to a peripheral protoplasmic layer, the blastema. The nacleas divides, 
and its products pass gradaally into the blastema, which is used up in forming the blastoderm. 

Bruce (10) speaking first of Bobret^ky's work, thus describes the formation of the blastoderm 
in Lepidoptera : 

In the earliest stagee he foand foar AnKehiform cells in the yolk, •ito»ted in, pairs at opposite ends of the egg. 
Later the hlastoderm is formed by a multiplication of these cells ; according to Bobretyky it is not formed siroultaneonsly 
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 net 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 nndifTerentiated cells do not, according to Bobretyky, reach the 
snrfiEMse to form the blastoderm, but some remain centrally located as yolk cells after the forniatiou of the blastoderm. 
The earliest stages of segmentation observed in Tkyridopter^x showed several amcebiform cells in the yolk in each 
cross section. 

In Thyridapteryx the blastoderm is first formed in a given area on the surface, afterward com- 
pletely inclosing the eggj 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 JuIuh terrestrit is described by Heathcote (19) as a syncytium. Seg- 
mentation is at first central, and the resulting nuclei are united by Htrauds of protoplaHm. Upon 
reaching the surface they spread themselves over it to form a blastoderm. The blastoilermic 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 corresi>onds to a similar stage which is met with in 
Schizopods, Isopods, Myria|KMls, to the primitive cumulus in Arachnids and the ventral plate 
which suffersinvagination in some insects. Possibly it corresponds also to the invagination plus 
the thickened ventral plate of Alpbeus 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 
diffuse over the egg^ but segment to form a thickeneil plate. 

Balfour says, in speaking of forms like Penaeus : 

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. i, p. 113.) 

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 sufiQciently 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 oyum does not always take place before segmentation, but is sometimes deferred till even the later stages 
of this process.— (Comp. Embryology, Vol. i, p. 110.) 

In most cases the protoplasmic segmentation is at first central^ or, as Kingsley i>oints 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 insects, says : 

He regards the nuclei surrounded by protoplasm, which are produced by the primitive segmentation nucleus, as 
so many distinct cells. These cells are supposed to move about freely in the yolk, which acts as a kind of interoel- 



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MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 425 

lalar roediam. This view does not commend itself to me. It is opposed to tany own obserrations on similar nuclei 
in the Spiders. It does not fit in with oar knowledge of the nature of the ovum, and can not be reconciled with the 
segmentation of such types as Spiders, or even Eupagnms, with which the segmentation in insects is undoubtedly 
closely related.— (Comp. Embryology y Vol. i,p. 119. ) 

This discossion seems to have arisen from a confasion of the morphological and physiological 
sigDificance 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 a secondary 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 nnsegmented 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 eggy whether superficial or 
amoeboid, 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 TOLK. 

There are traces of a secondary segmentation of the yolk in Alphens 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 Pis. xxx- 
XXXV In one eggj 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 Oniscns and Pala^mon. In PalsBmon 
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 Kusbaum (44) that a part of the endoderm of OniscUvS 
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 Alphens 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 anomalons " secondary cells,'' which have been a sort of outstanding 
puzzle to embryologists, receive, 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- 
onic 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 wfth ^|^Uf^o|p 



426 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 

nodu]e8 iu ite meshes, begin to show retrogressive tendencies. They sometimes ap|)ear swollen ont 
to an nnusnal size, and their chromatin is aggregated into a single large ball, which may become 
vesicnlar and strongly refractive. The chromatin ball is sometimes of large size, central in posi- 
tion, and staineil 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 fille<l with numerous coarse grams. 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 breai^ down and thus set tree into the yolk the naked, spore- 
like masses of degenerating chromatin. 

In Figs.2I and 32 (Pis. xxvu, XXIX), taken from the egg-nanplius embryo, we see various stages 
of this process. Around the stomodaeum, and within or near the pockets of the antennae and mandi- 
bles, there are large numbers of these pseudo-spores. Some are small chromatin balls (s), which 
combine actively with hsemotoxylon, while others stain feebly or are quite unaffected by the dye, 
and resemble straw-colored particles of vesiculated and altereil food yolk. Below and to either 
side of the stomod^eum there is a granular residue (Fig. 118, A. Y. S.), composed of yolk 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 api>ear 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, 6,/, or h for instance, correspond to similar fragments 
which occur free in the yolk. The larger nodule in the nucleus / 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 c resembles figure b^ except that the outer light zone is 
larger in c and the chromatin or stainable residue has nearly disappeared. I regard the bodies b 
and e as masses of degenerating chromatin which have escaped from a disrupted nucleus or cell. 
In c the retrogressive changes are furthest advanced. Finally, when the chromatin or stainable 
matter has been completely disorganized, there is left a vesiculateil 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 resembling b in Fig. 18 (see Fig. 21, s, 8^ 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 resemblan(je 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 Big. 19 and that of an embryo iu Fig. 35. In e<ach 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. O.) 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-xxxixand xli-xjliv), 
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 (PI. XXIX, Fig. 36; PI. XLVi, 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 seey in Stage iv, and in the following egg-nauplius stage they are 
abundant. In Stage Vii (PI. XLiv, Fig. 131) they are still present, and in Stage viii there is a 
fresh irruption of degenerating products into the yolk, arising from the centripetal cells of the 
dorsal plate. At a slightly later period they have almost wholly disappeared. Even as late as 

iu the tenth stage a few chromatin granules can be seen in the region of the dorsal plate, i OOqIp 

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MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 427 



CELL DEGENERATION AND AMIT06IS IN ALPUBUS MINOR. 

In the segmeDtation 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, PI. xxviii, 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 olf 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 sta*ge in the crayfish. 

The egg sectioned in Fig. 12, PL xxvi, 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 (sgg 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, 1 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. 

CELI. DEGENERATION IN ASTACUS AND HOMARUS. 

Homartis 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 Ilomarus 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 
stomodsBum. A long nebulous train of yolk spherules and grannies extends forward a considef - 
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 occur in connection with the endoderm cells, which have at this 
stage extended through a greater portion of the egg and form a series of irregular sa<5s filled with 
yolk. These yolk masses, with their surrounding 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- 
plasmio body. The degenerating chromatin stains either very intensely or faintly and is often 
vesiculated; that is, it appears as a hollow shell. Under favorable conditiousit is easy to demon- 
strate the fact that these bodies surround particles of yolk, and occasionally they have a crescentic 
shape, when it can be clearly seen that they are enwrapping a yolk spherule. This vitellophilus 



* While this memoir was io press a paper was received on AmitosU in the Embryonal Envelopes of the Scorpion, by 
H. P. JohnsoD, (BnUetin of the Museum of Comparative Zoology, Vol. xxii, 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 Blatla germanica, Mr. Johnson finds that degen- 
eration does not always follow upon indirect ceU division, as in the case of arnitosis in the testicular cells of certain 
Isopods. 



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428 MEMOIRS OP THE NATIONAL ACADEMY OP 8CIBN0E8. 

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. 

Astdcus (?) — I have studied several critical stages in the development of the craytihh, critical at 
least so far as the appearance of degenerative products is concerned, with an eye to comparison 
with Alpheus and Hoinarus.* The youngest set of embryos corresponds nearly to iieiclienbach's 
stage E, but differs from it in some details. Rudiments of five pairs of appendages are present, 
the two maxillsB being iieen 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 antennie. 

The bodies which Reichenbach calls << secondary mesoderm '^ occur in abundance in or near the 

wall of the endoderm sac 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 

, behind it. In this respect they recall the distribution of similar bodies in Alpheus and Homams. 

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. vin, 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 Homarns. Whether these cells in Astacus are simply migrating in a column or sheet, 
spreading gradually towards the periphery of the eggy as in the lobster, cannot be decided from the 
material at my command, 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 desfcribed 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 outlines of vesicular bodiea which exhibit but slight reaction«to the stain. These I 
regard as degenerated cells. 

The next stage of Astacus which I have studied corresponds nearly to Reichenbach's stage G. 
Eight pairs of appendages are present, and there are rudiments of a ninth pair. The first and 
second maxillae 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 coa^ulable fluid which comes in close rela- 
tion with the posterior end of the embryo. The endodermal cells laterally have quite or nearly 
reached the ectoderm, while dorsally they fall a little short of the surftvce. The yolk within the 
confines of the endoderm has an irregular, pyramidal, or radial cleavage. Centrally the yolk 
Mends with the serum-like fluid, in which occasional grannies or balls of chromatin may be found. 
Small spherical elements (like those represented in Fig. 18, a, 6, c, or fr, 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 sa^^ 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 opportnuity of Rtudying the crayfish ilevelopment at this time I am indebted to the kindness of my 
friend, Dr. William Patten, who sent me a namber of important stages collected at Milwaukee. 



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MEMOIRS OP THE nItIONAL ACADEMY OP SCIENCES. 429 

Eeicbenbach thas sammarizes his observations on the *^ sekandare Mesodermzellen :" 

Die fraglioben Elemeate sind als Zollen zu denten, deren Kerne nicht iminer die BeschaffeDheit gewohDlicher 
Zellkerne habeu, dieselbe aber friiber oder 8pat«r erlangen (Fig. 20, m, m*, Plate xxvit). Sie nebnieu ibren Ureprung 
inuerbalb dorjeuigeu Eutoderfbztillen, welcbe die ventrale Waud des UrdarniBackoheus zusatniuensetzen durcb eiue 
naber zu erforacbende Art endogeuer ZellbiduDg, bei welcber die in der Mebrzabl in den Elemeuteu des Entoderms 
vorbaudeuon Kerne eine wicbtige Rolle zu spieleu scbeinen. In den dem Stadinm D vorangebenden Entwicklung- 
sperioden bat jede Eutodermzelle meist nur einen Kern ; dies trifft aacb nocb zum Tbeil fiir Stadium D zu. Bald ver- 
mebren sicb aber die Entodermkerne ganz erbeblicb uud eudlicb beginneu die sekundareu MesodermzeUen aofzutreten. 
Weun eiue grussere Zabl der sekundiiren Mesodermzellen iu den Entodermelementen liegen, so scbeint das Kernma- 
terial verbraucbt zu sein. Es wandern nun aller Wabrscheinlicbkeit nacb diese Zellen, deren Kerne ansobeinend 
nocb in dor Metamorphose sicb beiinden, aus dem Entoderm aus uud begebeu sicb unter die Embryonalanlage. Die 
betreffenden Contouren des Entoderms lassen oft nocb Spuren dieser Wanderuug erkennen. Ob sie wir^icb aktiv 
auswaudern odor aucb ausgestossen werdeu, ist nicbt festzustellen gewesen. Sie begeben sicb nun unter die tibrigen 
Mesodermzellen und sind bald nicbt mebr von ibnen zu untersobeiden. Aus diesem Grund fUbrte iobfursiedeu 
Namen '*sekuudaro Mesodermzellen'' eiu, wiibrend die alteren Urmosodermzellen als primare bezeicbnet werden. 
Da die letzteren die Tendenz zeigen, zu kompakteren Massen zu verwaobsen, so dorf man wobl vermuten, dass die 
sekundiiren Mesodermzellen die Blutzellen liefern werden (54, p. 36). 

It is interesting to notice that in Alpheas, Astacas, and Homarus degenerating oells appear 
in greatest force at about the eggnanplitrs stage^ and from that time on their numbers begin to 
wane. In Astacus, Beichenbach first noticed the ^^ sekuudare Mesodermzellen" iu stage D (that 
is, when the optic disks, the thoracic-abdominal plate, and the mandibles are outlined), which nearly 
corresponds to Stage rvr of Alpheus. In stage D the bodies in question are most abundant under 
the optic disks (Kopflappen) and in the region of the upper lip, but become more generally dis- 
tributed iu 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 surftice, to the time when an embryonic 
disk or plate (Bntodermhugel or Bntodermscheibe) has been formed. It is impossible, therefore, 
to follow the history of the so-called " white yolk elements.'' He says of the latter : 

Sie besteben aus protoplasmatiscber, feinkomiger Substauz und entbalten vacuolenartige EinscblUsse, die ibnen 
ein scbaumiges Ausseben geben ; icb babe sie als weisse Dotterelemente bezeichuet. Sie liegen entweder dicbt unter 
dem Blastoderm oder im Centrum des kugligen Eies und verscbwinden sebr bald (Op. cit., p. 7). 

According to my view these bodies correspond to the vesiculated elements (w. 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 botl^ 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 sac. 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 api)earance at nearly similar times and play a similar r61e. They are derived 
from all three, layers of the germ, and in Alpheus minor degenerative products make their appear- 
ance in the segmentation stages, f hey 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 3 they are converted into a substance 
resembling yolk and function as nutrition. That any play a formative r61e, giving rise to blood 
cells for instance, as Eeichenbach 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 
amoeboid,' endodermal cells. This is reversing the account, and, in so far as the origin of the "sec- 
ondary mesoderm" is concerned, it is not supported, so far as I am aware, by a sin^e obsuy:vation. j 

Digitized by LuOOQ iC 



430 MEMOIRS OP THE NATIONAL ACADEMY CP 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 traoe 
their origin or function. They are ^^ small granules,^ easily stained by logwood solution, and some 
are of considerable size and have a clear cell outline. *^ These are mostly aggregateil 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 corresi>ond 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 pa|>er represents a longitu- 
^ diual median section of the eggnanplius, and may be compare^l with the same sUige of Alpheus 
(Figs. 104, 105), with respect to the general character and ai)|)earance of the degenerating cells. 

I have noticed similar nuclear fragments in the egg-nauplius of a crab (Fig. 113, PI. xL), and 
Lebedinski (34) has described ** secondary mesoderm'' in the embryo of the Metliterranean sea. 
crab, Eriphia Hpinifrons. According to this observer they are found in all sUiges from the ^^ gastrula" 
on, to the egg-nauplius; they are derived from ectoderm, and probably give risi^ to blood cells. 
In the stage with one pair of maxillipeds these elements are in active proliferation : 

Mau findet, die Zelleo desselben bieten venchiedene Momente nnd ZnHtiinde dea ZerfulleDs dar ; dietten ZerfaUen 
der Zelleu Htoht in geuaaen Zosammenhange mit der Entstebung der Blutkorper. 

He further says : 

Ueber die Bildung de» Bin tea kann iob nichta bestimmt^s mittbeiloD. Im Stadinm dm ersten Paara kieferfuHsohen 
sind die ersten Blutkorperchen vorbandciiy welcbe zam ersten Mai iin Beroiche dea Herzens vorkoiumeD, woaich anoh 
am friibeBten das sekundare Mesoderm rttckzabilden beginut. 

From these quotations it appears that the ^^ secondary mesoderm " shows signs 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 deeemlineata) describes an interesting case of the decomposition 
of nuclei, which bears a close analogy to what takes place in Alphens and probably also in 
Astacus. In Doryphora two masses of endoderm are found, one under the stomodseum the other 
under the caudal plate. At both these plac/cs numerous cells which originate in the endo<Ierm 
pass into the adjacent yolk and disappear. The process of dissolution is described as follows : 

Tbe karyocbylema becomes vacaolated, probablv with snbBtances absorbed from without, to judge of the larger 
size of some of these nuclei, while the chromi^tin 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 themi^lves to the wall of the clearly vesic- 
ular nucleus ♦ * • 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 f. Fig. 88 of Wheeler's paper, where the chromatin is applied to the walls of the 
nucleus, strikingly resembles nucleus «, Fig. 20 (see this paper), where the chromatin 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 Eeichenbach 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 amoeboid movements, while 
the nuclei elongate, become constricted, and finally fragmented. " The multinaclear stage • • • 
is probably followed by a complete dissolution of the cell." Howell adopts the highly reasonable j 

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MEMOIRS OF THE i^ATIONAL ACADEMY OF SCIENCES. 431 

view that the nuclear fragments persist for a while in the circulation as the blood plates, and 
considers it probrable that the latter take some part in forming the paraglobuliu 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 ALPHBUS. 

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 into the yolk (Pis. xxxii-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 cells.'' Since these classes can not be distinguished after a 
certain period, 1 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. I have 
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 role they play while the mesoderm, and more particularly the endoderm, are being 
differentiated into definite cell layers. In the following account, cells which have ])arted 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' iii-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 more precise study of the 
wandering cells 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 ii~v.) This covers the most important period so far as 
the wandering cells are concerned. The 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 re|erring to the embryo proper and to the less differentiated regions, while 
it is understood that all the cells constitute the embryo. 



Digitized by 

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432 



MEMOIBS OF THE NATIONAL ACADEMY OF SCIENCES. 



Tablb LShmoing the number of nuclei in 3K>tt, and the number of other " embryonic nuclei,^ and the 
relative increase and decrease in these bodies from the close of yolk-segmentaiion to tl^ egg-mtuplius 
period. 



Stage. 



II. DelaminatioD (Figs. 38-45, 46, PI. 

XXX) 

TT T«^o^«;,.«*:^«K<») Figs. 49-55, PI. XXXI 

III. Optic disks (PIh. xxxii, XXXIII) 

IV. FirstaDteDD£B,iDandibIett( Pis. XXXIV, 

XXXV) 

(a) Figs.34,Pl'3txix;| 



V. £arly egg-naa- 
plius 



101-105, 107, PI. 

XXXIX 

(ft) Figs.34,Pl.xxix;i 
101-105, 107, Pl.V 

XXXIX ) 



id 

o o 

a 
& 



•34 
•37 
•37 
199 

240 

199 

128 



15 

cJS 



l£% 



82 



3 

3 

162 

41 



41 
112 






284 

421 

430 

t736 

t915 

t2,989 

t2,«30 






if 



il' 



\^ I 



8£ I 9-^ 

81 8o 



-I 
11 



137 
146 
306 

179 

2,074 

1,315 



II 



il 



I 



318 

458 
467 
935 



140 
149 

468 



1. 155 j 220 

3,lt<8 ! 2,033 

2,3.'i8 I 1,203 

I 



8 

8 

17 



21 



874 



32i 

34 

42 

20 



59 



* Primftry yolk cells. 

t Number obtoined by method described bdow. 

The distribatiou of the wandering cells and of the embryonic nuclei 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, etc.), while each 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 eggj corre6iK>nding 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 i. Stage iii-v) where this method became impracti- 
cable with reference to the total number of embryonic nuclei, 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 i)ercentage 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 smaller, showing that the yolk cells were, on the 
average, a little larger than the other embryonic nuclei. In Stage ii before invagination the sui>er- 
flcial nuclei are the larger, while after invagination the diflference is at first very slight indeed. 
In Stages iii and iv the wandering cells are markedly the largest in the eggy while in Stage v 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 (i°*™, or ^ inch in diameter) was cut, on the average, into 
67 sections, each section being TiT™°* in thickness. The size of the egg, neither too small nor too 
large, rendered this species (called throughout this paper the Bahaman variety of AlpTievs heter- 
ochcHs) most favorable for study so far as technical difficulties were involved. 

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Digitized I5y 



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MEMOIRS OF THE NATIONAL ACADEMY CF SCIENCES. 



433 



Stage II. — Close of yolk segmentation — Formation of yolk cells, folloiced by invagination. A • 

flurface view of this egg is given iu Fig. 47, PI. 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 oflf. The distribution of 
the primary yolk nuclei, of which there are exactly thirty-four, is 
shown in the constructed figure (Fig. 3), which represents the egg 
as it would appear if the yolk were tra^nsparent and the nuclei 
opaque. The distribution ofthese 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 comet 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 Fm. 3.— niagrani of egg in deiamination 
portion of the yolk. Clusters of two and rarely of three nuclei also "^e*; *^»f y"*^*«i «^™ ««;?»» ««^**«»«. 

'^ •f •f Hhovring all the primary yolk cells. For 

occur at the surface, showing that cell division is active. In every details, s«e Tabi© i. stage n (Deiamina 

case the cleavage is radial or perpendicular to the surface, and in no ****°^- 

instance have I seen an unambiguous case of deiamination (v. PL xxx). It is possible, however. 




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^ Flo. 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 i, Stage ii (Dehunlnation). J.— Anterior; /»= Posterior. 


ij ^ ■ ■ -- ■■" " ^ *~ 




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V\Q, 5.— Curve showing the distribution of nuclei at the surface (that is, nuclei of the embryonic cells, i^jcMj^esI^ l9^°^ik£ll^xi} i^^^ Lv^ 
of the egg represented by Figs. 3 and 4. For details, see Table I, Stage il (Deiamination). C3 



S. Mis. 94 28 



434 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 




that the primary yolk cells are formed iu thin way rather thau by emigratiou, and that my failure 

to detect the actual procesn in due to the fact that I did not sec- 
tion exactly the right Htage, the egg nhown in Figs. 38-45 being 
a trifle too old. In Uomarun the primary yolk cells arise by 
delamination, as 1 have already shown iu 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 alremly reached. 

The formation of primary yolk cells is followed by the in- 
vagination and ingrowth of certain cells at the surface. The his- 
tology of the embryo at this phase is given in PI. xxxi, and Fig. 
i\ (of text) is constructed from the entire series of sections to show 
all the primary yolk nuclei present. The plane of the paper (sup- 
l>osing the drawing to represent a sphere) nearly passes through 
the i>oint of invagination (//i.). 
In order to test the accuracy of the method, two eggs of this stage were studied (a, ii and ft, 
II oi Table i), and the results show a remarkable agreement. Thus there are exactly thirty-seven 
primary yolk nuclei in each eggy and the total difference in the number of embryonic nuclei iu 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 ^eeu in Fig. (ii, n, of Table i). Figs. 10 and 
9 represent corresponding curves constructe<l from the second egg (ii, b). The two sets of curves 
tell exactly the same story in each case, and it is not necessary to dwell Q|>on it. 



Fio. 6. — Diatn'iLiu of e^g iu iuvagiuatiuu 
HUge, constru<'t«d froo) serial m.-ctionii, to 
iiUow all the primary yolk nuclei preiveut. 
For flpt«il8 of this egg, Hoe Table I <ii,a), 
Invagination. In — point of invagination, 
nearly in the plane of the paper. 



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Fio. 7.— Carre constracted from serial sections, shoeing the distribution of the primary yolk nuclei in the egg represented by Fig. 6. 
(See Table i, Invagination stage, ii, a.) 

The bulk of the primary yolk nuclei are placed near the center. Of the thirty-seven nuclei in 
a, u, twenty-two are in the ventral (t) hemisphere of the egg, and fifteen in the dorsal. In egg b, 
II, 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 embryonic area. 

The curves showing the relations of the embryonic iiuclei (Figs. 8 and 10) read from end to 
end of the embryo (iK)sterior 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 (E. A.). The iiU'^V^r^ryT/> 
of cells entering into the ventral plate at this time are shown in Table ii. digitized by v^rrVJVJ^LL. 



MEMOIRS OP THE NATIOiJAL ACADEMY OF 801EN0B8. 



435 



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Fio. 8.- 
. (See Table I, 



Abp, EA. 

-Curve showing distributiou of all nuclei, exclusive of primary yolH nuclei, in the same egg aa represented by Figs. 6 and 7. 
Invagination stage, il, a.) J., Anterior; P, Posterior; Abp, Ventral plate; BA, Embryonic area. 











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^ KlQ. 9.— Curve showing the distribution of the primary yolk nuclei in the invagination stage, egg No. u, 6, Table i. (Compare with Fig. 7.) 






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Fio. 10.— Curve showing distribution of all nuclei, exclusive of primary yolk nuclei, in the same egg as represented by Fig. 9. (See li, 
&, Table I, and compare witli Fig. 8.) J., Anterior; P, Posterior ; A&p, Ventral plate; EAy Embryonic area. 



T 



436 



MEMOIRS OP TOE NATIONAL ACADEMY OF SCIEN0B8. 

Table II. 



SUk«. 



, «affa4« of I ^,^- *^;„^*' 



a, 11. 

b, II. 



I 



Total noin- 



Priraary 



'^n''Ib.''f"V""'-""='" 



Renalnlns TotAl nan- 
, ««mbrynnir berofnaolei 
I ouctei. of egg. 



56 
52 



60 

48 



116 
100 



37 
37 



305 

:»o 



458 
467 



Of tbe forty-eight to sixty cells which appear below in sarfaee at this time in the ingrowiDg 
cell mass, a large number (twenty in b^ n) 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. 

Stage III. — Optic di8k$ and thoracic-abdominal or ventral plate, — Wandering cells now become 
a very marked characteristic of the Alphens egg (Pis. xxxii, xxxiii). We see by Table i 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 othpr 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 thick- 
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 tbe thoracic-abdominal 
plate, while on either side of this there fs 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 the 
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 optic disks. Quite a number have started in the 
direction of the dorsal surface of the egg^ but none have reached it. 

Staqe IY. — Rudiments of First Antennce and Mandibles. — This is the most interesting stage 
in some respects (see Pis. xxxiv, xxxv), since it is critical so far as the fate of the wandering cells 
is concerned. 



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Fio. 11. — Cur^'e Rhowin*: the diHtribntion of wandering cells in Stage IV, mdimenis of first ant^^nnje and inandi^leflLnrgtenfL 

O A lieitrion of oplie dlHe:^]^ '^'^^^ ^y 



le 



MEMOIRS Of the national academy of schenoes. 437 

Table i shows the remarkable fact that the percentage of increase of wandering cells, which 
in Stage in was twice as great as that of other embryonic naclei, 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 ii to iii, and from 
Stage III to IV, namely, 81 percent and 17 per cent (showing a marked falling off), is not specially 
significant, since these numbers depend largely upon the ago of the embryo or time which elapses 
between successive stages. But this element does not enter into the relation which exists between 
the relative increase of wandering and embryonic cells in the same egg, expressed by 81 per cent 
and 41 per cent, respectively, in Stage iii and by 17 per cent and 20 per cent in Stage rv. 

The curve constructed from Stage iv (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 optic 
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 
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 
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 yc,Fig.70,or ^c\ Fig. 71, as a migrant from the yolk. While the wandering cells 
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 i, prove beyond a doubt that the only 
cells which enter the yolk, up to this time, arise from one of the three sources already named, the 
blastoderm, the invagination, and the ventral plate. 

Stage V. — Egg-NaupUus. — The early egg-nauplius stage is represented by two individuals, 
one (y. a, Table i) cut in transverse and the other (y. b) in longitudinal 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 y, b (Table i) the number of yolk cells is only one hundred and twenty-eight, consid- 
erably less than are present in Stage iii, 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 between Stages ly and y is shown by the fact that 
during the period (Stage ly and Stage y, by Table i) the total number of nuclei of the egg has 
scarcely more than doubled, while the percentage of increase of embryonic nuclei has more than 
trebled. Between Stages ii, a, and iii, on the other hand, the number of nuclei has nearly doubled, 
while the percentage of increase of embryonic nuclei has risen from 32^^ to only 42. 

How is this very rapid increase in embryonic nuclei and coordinate decrease in wandering 
cells explained in the egg-nauplius stage? The conclusion reached in Stage ly 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 the number of 
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 
the embryo. 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 cells, which spread far and wide 
through the egg^ play a formative r6Ie in development, to a large extent at least. This conclusion 
is rendered certain by the changes which ensue between Stages ii and rv, already ^^Ofi^^^f^ /%%!/> 



438 



MEMOIBS OP THE NATIONAL ACADEMY OE 80IBNCE8. 



percentage of iucrease of waoderiuK cells between Stages ii and ill is doable that of the embry- 
onic cells. Between Stages in and iv the increase per cent of wandering cells is less than that of 
the embryonic cells, and up to this time cell disintegration is mled oat as a distarbing factor. 







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Fio. 12.— Curve shoving distribution of waodericg cells in Stage v (Early egg^naapUns). (Compare Fig. 11, and for details, see Table 
I, Stage, II 6.) £ J., Embryonic area; Jfo, Koutb. 

The second fact which was pointed oat as characteristic of this stage, the distribation of the 
yolk nuclei commensurate with that of the yolk itself, also points to the conclnsion 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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Flfl. 13»— Curve showing the distribution of wandering cells in >>tage v, a. (v. Table i.) 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 ^(l^8^q|P 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 439 

and the embryonic area is included between sections 14 and 41. The marked peripheral distri- 
bation 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 the e^f^gl 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. In a 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. 34, 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 ii. Table i, 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 ectoblastic 
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 
(64) to originate in certain swollen cells in or near the anterior margin of the "blastopore'' or 
pit. From this primary mesoderm cells are budded oflf, 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 tropics the developmental 
stages are passed very rapidly. At Woods Holl, Mass., the late egg-nauplius of the lobster, 
Homarus americanuSj is from fourteen to sixteen days old, while a similar stage is reached by 
Alpheus saulcyi 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 (Pis. 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 suprao&- 
sophageal ganglia to the segment of the first maxillae. 

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 autennie (Fig. 116) it has the ap[>earance of an elliptical plate in trans- 
verse section. 



*'Welclon, whose paper on the germinal layers in Crangon has heen referred to, says truly that thedlffereDce 
between invaginated cells is not sufficient to enable one to say that certain cells are endoderm and that others are 
mesoderu), but he 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 be interpreted as mesoblast. The thoracic-abdominal thickening is composed of a pAir ^C^o^ai^ i >^ 
"nearo-muscnlar" or ventral plates, which correspond to the single plate described in Alphem^^cl by V^nW W V Lv^ 



440 MBMOIBS OF THE NATIONAL ACADEMY OP 80IBN0B8. 

The antennalar gaDglton in iu close union with the optic ganglion and unites also with the 
antenna! ganglion which lies along the sides of the stomodseam, extending slightly behind it 

The histological differentiation of the nervous elements is not very considerable at this stage. 
In the ectoblastic thickenings, oat 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. e.). They possess a more 
or less definite cell body of a round or oval contour. In preparations this is finegrained and, like 
the nucleus, stains but feebly. The weak stain of the nucleus is due to its very fine and loose 
chromatin reticulum. Earyokinetic figures attest to the multiplication of these cells (Fig. 191), and 
it i^ highly probable that they give rise to similar cells which occur iu both larva and adult. But 
what is remarkable in the earlier stages is their enormous size and their peripheral position. 
Beichenbach calls 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., PI. 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 cells 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 
Drain, are surrounded by a delicate cell layer or internal envelope. Tlie nuclei are small and 
spindle-shaped and form an exceedingly thin sheet. It is possible that this represents intrusive 
mesoblast, derived from the yolk. Beichenbach 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 ectodermic origin, but the behavior of the 
wandering yolk cells renders it probable that they should rather be referred to the mesoblast 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 
antennae on their dorsal surface next to the yolk. Degenerating cells (Fig. 114 s^) occur 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 x)eripheral tier of cells possessing large 
granular nuclei, an inner layer with smaller nuclei, and an imperfect layer of investing cells. 

Passing to Stage Yii (PI. XLiv) we find the nervous system still very rudimentary. The super- 
ficial cells, particularly in the region of the optic lobes and the antennsB, 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 Q. L.) with the antennular ganglion {S. 0. 0.) is still very 
noticeable, and the delicate investment of these parts on the side of the yolk (mes,) is more 
marked. 

Punctsnbstanz has definitely appeared in the supraoesophageal ganglion where there is a 
marked transverse commissure, and can even be distinguished in the (Bsophageal 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 ectederm ^^^^T^ 
cells. Digitized by VnOOQlC 



MEMOIRS OF THE IfTATIOiTAIi ACADEMY OP SCIENCES. 441 

The paired structare of the ectodermal plate is well sbown in the aateuuular ganglion on a 
level with the transverse commissures, or even in front of this, where paired masses, with small, 
deeply dyed nuclei, are separated by a mediaA sheet of much larger and clearer cells. This may 
possibly correspond to the mittelstrang, referred to again. 

Shortly after this (Fig. 139) 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- 
oesophageal ganglia and passing to the last abdominal segmehts. The ganglionic blocks are 
formed rapidly from the front backward. The ganglia of the first antennje 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 (PI. xxyi), when eye pigment is forming. From this commissure longitudinal rods 
extend forwards and unite the brain with the optic ganglia, while similar rods grow backward and 
form the fibrous axis of the circumoesophageal commissures. 

The plane of sectioa in Fig. 148 passes just in front of the (Bsophagus and through the roots 
of the first pair of antennse (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 antennae, 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 wJiich 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 biisement 
membrane of the hypodermis. The cuticular sheaths of the nervous system are present in the 
embryo (Figs. 157, 168 j>r.), 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) concludes that in Doryphora the "outer neurilemma'' 
is ectodermic rather than mesodermic in origin, since — 

Shortly after the separatiou of the nerve cord from the intefi^utuentary ectoderm, it sheds from its snrface a deli- 
cate ohitenoas cuticle simultaneously with the shedding of the first integumentary cuticle. This cuticle, which is 
separated from the snrface of the outer nenrilemnia, 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, 
and the 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 infoliliugs 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. 16S) spindle- 
shaped nuclei are seen wedged between the nerve cords on the middle line. It is not, however, 
certain that these cells are ectoblastic, since the sternal blood sinus is already formed, to which j 

Digitized by VnOOQ iC 



442 MEMOIRS OP TUB NATIONAL ACADEMY OF SCIENCES. 

blooil cells have penetrated, and here eventually the sternal artery is developed. While the evi- 
dence is not conclusive, we have only to (tecide between the former conclusion — that the intrusive 
tissue is derived from the wandennp: cells, and is to be referred to mesoblast, or the view that it 
represents differentiated eotoblast. 

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 Keichenbach for the crayfish, Astacus fluviatilM^ 
there are numerous particulars in which there is no agreement, while in some im|K>rtaQt 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 have a great many preparations of the eggs of the lobster, Homanu ameri- 
canusj which show the earliest traces of the stomodseuin. Before thc^ first aiitennie 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 antennae 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 antennae are 
clearly marked off as rounded buds, and l>efore the second pair are raised into folds, the mouth is 
still on a line with the first of these appendages. When the second antennae are elevated into 
folds the mouth is behind the buds of the first pair, or on a line between their posterior edges. 

Beichenbach (taf. ii, Fig. 7a, L6.) describes and figures a cell thickening between the "Kop- 
flappen" of the crayfish embryo (Stage B), which he considers the beginning of the labrum. His 
sections show that below this point a mass of ectodermic cells occurs, which is interpreted as the 
"Vordarmkeim.'' The mouth is not represented as ap[K»aring until the following egg-nauplins 
stage (Stage F. Compare Fig. 66 and p. 100, § 7, " Der Vorderdarm^), when it occupies a position 
exactly comparable with that observetl 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 iwstoral, it may be questioned if 
in the higher Crustacea the first antennje 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 not mistaken in this particular. 
A single rudimentary appendage, marked as the first antenna, 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 wt, in Kingsley's paper, as 
the invagination of the mouth. t 

In Alpheus, Homarus, Astacus, and probably in Decapods 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 6r supraoBsophageal 
ganglion. The ganglion of the first pair of antennae is constricted into two portions marked by 
an oblique, transverse line at the surface. The anterior of these parts Beichenbach calls the 



* I have preparations of the eggs of Crangon vulgarisj 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 Alphens 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 stomodaBiim is on the middle lino between the first and second antenna), and the anten- 
nular ganglion is segmented into two parts on each side, as shown for Alpheus in Fig. 110. 

tThis criticism is supported by Weldon's observations on Crangon, who, with reference to this subject, says: 
*'The first antennae are evidently prsooral from the very earlieait period at which the mouth is_yisible." lP^ oit./^ /^ rj I /> 



MEMOIRS OP THE NATIONAL. ACADEMY OP SCIENCES. 443 

"vordere nirnanscliwellun^^ aud the posterior the "SeitenanschweUung," uning the terms of 
Krieger and Dietl. Xh^s^) latter particulars accord with Beicheo bach's description of the crayfish. 
I have not, however, found that in Alpheus, behind the level of the first pair of antennae, the lat- 
eral parts (Seitenstrange) divided up into three sections. Eeichenbach 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, it 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 furcae. 

According to Eeichenbach the lower oesophageal 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. 

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 p^nctsubstanz balls, one ball in each single ganglion. These extend forward 
and backward, uniting the ganglia into qhains and forming the longitudinal commissures. A little 
later the transverse commissures are formed by bridging the cords between the points occupied by 
the fiber-srtbstance 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 mesoderm cells. He thinks, however, that since many structures like the optic gan- 
glion, the crystalline 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 Unfcersohung der wanderbaren Entwicklaogserscheinnngen in der organischen Welt aber driingt sicb 
bei tieferer Betraobtung immer wieder der Gedauke anf, daas man schon vom ersten Stadium an einem untreonbaren 
Ganzen gegenttberstebt. (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 the differ- 
entiated state. It seems morel 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 I have made on the develop- 
ment of nerves (see section i) refer to those of the first and second antennae (PI. lv. Figs. 
213-216, n. au.j n. a. g,; PL LVii, Fig. 243, n. au.). The antennular nerve. 



nerve, which supplies-^T^ 
Digitized by VnOOvlC 



444 MEMOIRS OP THE SATIOKAL AOADBMV OP SCIENCES. 

the ear, appears to arise as an outgrowth from the anteunalar fiber ma^s of the brain (Pig. 248, 
a/*.). It consists of a fibrous portion leading directly from the fiber mass of the brain and of 
somewhat flattened, or spindle-shaped nnclei, which penetrate the cortex of nervous cells and are 
undoubtedly proliferated from them. Possibly the internal sheath is coutinued over the growing 
nerve. 

IX. ~THE ETES. 

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 eara- 
pace. In the larva, however, the eyes are both naked and possess long, movable peduncles (see the 
metamorphosis, PI. xxi). In Alpheus sanlcyi the optic stalks are reduced to a mere rudiment, and, 
though provided with muscles, they can possess but very slight power of movement. They meet 
on the middle line in front of the brain, over the roots of the first pair of antenn». 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 (Pigs. 209, 210, of 
larva). Two small hairy tubercles, outgrowths of the integument, occur on the inuer side of the 
optic 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 
Sqnillae, on the other hand, in which the burrowing habit is more characteristic, have undergone 
no such modification. 

THK MEDIAN KYK. • 

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, PI. xxii, where it is seen as a small 
conical papilla, lying between the basal joints of the antennules, and at the roots of tl)e compound 
eyes, very close upon the brain. This is the first instance I have noticed of the persistence of the 
nanplius eye in the adult. 

The general position of the median eye of the first larva of Alpheus saulcyi is seen in Figs. 
209 and 210, and the minute structure in Pig. 197. The pigment takes the form of an inverted 
Greek capital upsilon (^). 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 (Pig. 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 BYESTALK. 

The visual apparatus of the compound eye of a Crustacean consists of 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 ectx>derm 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 «Scieiioe ( Jannary, 
1892), " On the Xauplius Eye persisting in some Decapods," by Margaret Robinson. The median eye was observed in 
some ei^ht different species of the Carididos, iticlnding the genera Paloimou, Hippolvte, Yirbias, Cr&ngon, and P^K ^<^y<^T/> 

daius. Digitized by VnO VjV LL 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 445 

Alpheas la the ooly gen as in which I have found glands in the ejestalk. The^e 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 
antennae into the antennules, the eyestalks, the labrum, and the whole front of the head, so as to 
completely envelope the brain. The histology of 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 tissue. This is 
specially abundant below the basement membrane of the retina. It forms a continuous sheath 
for the optic ganglion, and is reflected over the optic peduncle and brain. 

By far the greater mass of tissues of the eyestalk belongs to the optic ganglion. This is 
composed of' ganglion cells (Fig*. 187), nerve fibers, and the peculiar fibrous tissue variously 
called " Punot-snbstanz" or " Ball-substanz," and "substance pouctu6e.^ 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 
punct-snbstanz : (1) la masse m6dullaire externe, (2) la masse m^duUaire interne, (3) la masse 
m6dullaire terminale. The external medullary mass is united to the masse m^dullaire interne by 
an internal ckia^ma, while a fibrous peduncle joins the internal medullary mass to the masse 
m^dullaire terminale. The nerve fibers which pass between retina and ganglion, he calls the post, 
retinal fibers, and designates as " optic nerve" the peduncle by whiph the optic ganglion is united to 
the brain. The distal mass of punct-snbstanz is styled lame ganglionnaire,* which he divides into 
a nuclear layer (couche i^ noyaux), a mole<^ular layer (conche moleculaire), and a cellular layer 
(couche ^ cellules ganglionn<iires). 

The pnnct-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 m^duUaire 
terminale); internal middle segment (masse m^dullaire interne); external middle segment (masse 
mMuUairJ externe); distal segment (lame ganglionnaire) ; optic nerve (couche des fibers post- 
r^tiniennes). 

OE3IERAL STRUCTURE OP 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 the ^^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 
tq^considerable variation in different individuals, and the shape and arrangement of the ommatidia 
may be very irregular in different parts of the saftne 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 Decaptxls, 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 ectodermic origin. 

* Th6 lame ganglionnaire is called ** Retina ganglion " by ClauB, who reganis it as the trne retina ; "das anssere T 
Ganglion opticum " by Carriere, and " periopticum " by HickBf>n. Digitized by V^TlOOQ^ ^-^ 



446 MEM01B8 OP THE NATIONAL AOADEMY OP SCIENCES. 

6TRUCTUKE OK TIIK OMMATll>IVM. 

Both a lack of time and of fresh material have preveuteil iiw from making a8 thorough a study 
of the structure of the ommatidium of Alpheus a&s I had wi^heil. The following account is based 
entirel^^ upon sections : 

The corneal facet is strongly biconvex (Pig. 200), the convexity of the lower side being the 
greatest. Its shape is usually hexagonal, but may be tetragonal, or sometimes nearly circular 
(as in A. heterochelis). There are two corneal cells to each lens. A single ommatidium is shown 
in Pig. 2(H). As in all Decapods, the cone cells which underlie the eorneauen are lour in number. 
The four segments of the crystalline cone (Pig. 208), which are secreted on the inner sides of the 
latter cells, are always separated by delicate boundary lines. The cone is papped by a mass of 
protoplasm in which the nuclei of the cone cells lie, although it is not always easy to distinguish 
them. This cap appears to be raised into a slight elevation whit^h 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. c PI. liv), as Parker (48) designates them, and at least 
seven proximal retinular cells (rtL). Parker discovered in Uomarus 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 Pal»- 
monetes. The seven proximal retinular cells secrete on their inner sides the rhabdom or rhab- 
domeres. A transverse section of the rhabdom gives the |)eculiar seven-pronged figure shown in 
the drawing (Pig. 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 retinnl&r 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 l>eneath the cuticle of the larva of Decapods in various parts of the body. It is not 
decolorized 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 nitric acid. These cells penetrate the base- 
ment membrane, beneath which there is a considerable mass of both yellow and black pigment 
The trains of cells 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 retinulav cells. In Pig. 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 drai>ed in black. 

ARRANGEMENT OF THE OMMATIDIA. 

In Alphem sauloyi the ommatidia are arranged in a hexagonal system, subject to variations 
in dififerent 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. I have examined the 
cornea in four other species of Alpheus, namely in Alpheua 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 tho largest size were selected aud the cuticle was cleaned by boiling in a T 

concentrated solution of potassic hydrate. Digitized by VItJ 005 ^-^ 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 447 

facts in connection with the arrangement of ommatidia. In Alplieus 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. Alphetis mhior 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 opi)osite 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 luljoining 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 perij)hery, the facets of this row soon tend to become alter- 
nate with those of the row next to it. 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 Alpheutt heteroclwlift the facets in the larval ^ye are markedly hex- 
agonal. In the adult there is the same curious transition from the hexagon to the square as we 
have noticed in Alphetis 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 Alpkeus 
heterochelis the faci^ts are characterized by much greater looseness of arrangement, there being 
large interlenticular spaces. The facets are squares with rounded 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 8i>ot 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 Alphem 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 keterochelis 
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 all 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 ceils 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 keterochelis 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, i)articularly 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 S-O"**" (first larval stage) ; (2) length ll*"'" (fourth larva) ; (3) length 15.3™^ 
(sixth larval stage) ; (4) leiigth 49™°» (lobster 1 year old). 



* A similar trausitiou of the square into the hexagonal facet iu the same eye occui'h in Astacus. See Iloweb' j 
Biological Atlae, Fig. 111. Digitized by LjOO^IC 






448 MEMOIRS OF THE NATIOIJAL ACADEMY OF SCIENCES. 

In the first larva of both Homarus and Alphem saulcyi I fiud that the facetH are not ouly hex- 
agonal but tend also to be slightly roanded. In the larva ll"''" long the lenses tend to become 
square toward the center of the cornea, while at the i)eriphery they are smaller and generally hex- 
agonal. Occasionally, hoWever (just in what part I did not ascertain), the i)eripheral 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 in a 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 
differentiated. The corneal fetcets 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 lies 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 transition 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-inoh 
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 f 

Parker (48), who ha^ made a careful study of the arrangement of the omraatidia in different 
Crustaceans, recognizes two plans on which these organs are groupeil, the hexagonal and the tetrag- 
onal. He says that ^Mn the Brachyura, as well as in three families of the Macrura, the Hippidss, 
Paguridae, and Thalassinidse, 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 in size and the con- 
sequent crowding of the ommatidia, and reaches the conclusion from 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 and keen powers 
of vision, permanently adopt the hexagonal arrangement. The lower Macrura adopt both methods, 
and in certain species of Alpheus, as Alpheus minora 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 peripanency 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 an 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 ey^ 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 senses 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. 

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 leonditions it must 



gle 



MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 449 

have varied and attained to a new strnctare during the coarse of the evolution of the Brachjoura 
from Macrouran ancestors. 

Many crabs like the sand crab, Ocypoda arenariay si>end a good portion of time out of 
the water and their eyes are admirably adapted for virion 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 from the diflSculty 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 one for tubes with elastic walls to assume when 
thei*e 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 point 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. 

If 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 change. 

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 noticeable 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-veutral direction. 

In Alpheus saulcyi 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 (13'"*» 
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 zoea to the megalops stage than in the case of 
the lobster in going from the first t^o 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 it preserves a nearly cylindrical form, althongh 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. 

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The primitive arrangement of the ommatidia was probably in the form of simple tubes oi^ 
(\Tlinders, with spaces between them and with rounded or indefinite facets. Mutual pressun* 
amon^ these tubular eyelets, arising from any cause, produces tftrt iiexagonal arrangenient, the 
most economical method so far as wall space is concerned. Interferences such as have been sug- 
^ented, as growth of incMvidual ommatidia or increase in the Duml>er of ommatidia in the same 
urea, 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 th*^ hexagons into squares (the apparent slipping of the rows of facets on one another), may 
enter as factors into this change, but they do not suffice to explain all the conditions. It will be 
m Ml nrs rood, of course, that there are no changes in the individual facets, these remaining in the 
HiiirK' nhape until they are cast off in the moult. The changes which the individual ommatidia 
uiidyj^o are very gradual, and since the number of cells for each ommatidium is constant and deter- 
mined ut a very early period, excepting the accessory pigment cells, they must be attributed to 
tln^ ch;ui>];e in the size and relative {>ositions of the cells themselves rather than to intussusception. 
It in \)uAn\b\e that the change from the hexagon to the square is not produced in the same way in 
all t^ust-s and that the conditions of growth which bring about this result are far more compli- 
cated tljiiii would appear from the suggestions which have been maile. A careful study of the 
arranf^i'ment of cells in the ommatidia of the eye of the young lobster during the period of transi- 
tion won Id possibly throw some light upon this interesting subject. 

THE DEVELOPMENT OF THE COMPOUND EYE. 

V 

Five years ago (20) I stated my conviction that the compound eye of Alpheus, and probably 
sXm of Palaemontes and of the large Iso{>od, Ligea oceanicay originated irom a thickening of the 
HLiperticial ectoblast. The development of the eye in Alpheus was more fully described in a pre- 
liminary notice (21). I will now recapitulate the main resultn, at the same time correcting such 
errors aa I have detected. 

Iti 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- 
ferent) litioii of the retina into ommatidia or eyelets; the differentiation of the optic ganglion and 
the ilevelopmeut 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 tlie Optic 2>i«Ar.— The optic disks (Fig. 58, PI. xxxii) consist of large ectodermic 
areaB 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, 

Po far as I am aware we have no account of the origin of the optic disk in any Decapod except- 
ing Aljiheus, Astacus (54), Crangon (30), and Homarus (47^. Parker, in his careful studies on the 
©ye of the lobster, was unable to obtain the earliest traces of the developing optic disk, and the 
inreiHiuts of Reichenbach and Kingsley differ very materially. I will therefore describe somewhat 
in dt^tail the process by which the optic disk is produced in Alpheus. 

Tlie optic disks at the time when they consist of a single stratum of cells are shown in Figs. 
58^ flH, and 69. A series of four transverse sections through the central portion of the left optic 
df ak 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 
wbrrh 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 Qgg nauplius (Figs. 107, 114)? If the 
eye represents a series of hypodermal pits, it would be reasonable to look for some trace of these 
in foldings 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 
pri>^itracheate Peripatus, we should expect to find some trace of an involution at this stage. So thfi 
una wer to this question may have an important bearing upon the phylogeny of the compound eye. 

Ct'll boundaries are easily discernible at the surface, but it is evident that the nuclei do not r 

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all lie at the same level. Passing now to Stage iv (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 PI. 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 undergfoing 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, 0. 3f.;. 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 (7. M. (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. Thns the cell marked ec in 
Fig. 80 is distinctly below the surface. The boundaries of the cell can be clearly seen. The cell 
eo 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 lo.wer level. I inter- 
pret the latter as a cell at the point of breaking all connection with the surface and migrating to a 
lower i)08ition. 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. At a 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 optic 
disk is thus due in part to delamination, and 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 iii (PI. xxxnt) \^andering cells, or cells which travel through the 
yolk, have not appeared in the neighborhood of the optic disks. In Stage iv (Fig. 70, F. 0.) they are 
not far away, and in later stages (Fig. 91) these cells are close upon the disks. Some of them which 
enter this region, coming near to or uniting with the disks, undoubtedly degenerate (compare F. C, 
Fig. 94, «-«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 ^gg- 
nauplius (Fig. Ill, 0. L)j can be seen by reference to the plates (Pis. !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 VII. A deeper layer from which the ganglion is developed (Figs. 129, 132, G. L.) is gradually 
separated from a superficial tier of cells with very large nuclei {OE). 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 (J5m.), which is continuous with that of the surrounding hypodermis. 



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W^ndmiig cells are seen in contiu^t with tbin membrane (Fig. 130), hut they probably do not 
^ihare in irs secretion, although they occur in the closest relations with it. 

At a little later i)eriod (Fig. 13S) the retinal portion is several cells thick on the outer edges 
of the Inlw, while it is a single stratum in the sagittal section, shown in P'ig. 1*38. The plane of 
secttan is iie^r the center of the lol>e. The dee[>er nuclei of the ganglion are large and clear, the 
outer uiH smaller and stain more intensely. This section can be clearly understooil if compared 
with thn transverse section, Fig. 146. We see that the optic ganglion is here divided into an 
extenml or distal part and an internal or proximal portion by a thin sheet of very large and clear 
g^nii^Uoa cells. Parker (47) describes and figures an exactly similar structure in the lobster, and 
1 fiiMy agree with him iti regarding this band of nuclei as representing simihu* bands, which 
UeicliiiibMch (Taf xii. Figs. 173, 174,^. W. I. W.) describes in the cniyfish. In Keichenbach's 
plati^s these nuclei appear as a narrow fold, forming the lining of what is described as a secondary 
optic Jnvugination. 

Tbree punct-substanz masses have already api>eared 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 pmximal 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. 1G7) has disappeared. In front of it is developed the lame gang- 
lionaire ov 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 b^' a 
special layer of ectoderm cells. These appear in section as a single row of elongated nuclei. 

In an early communication (20) I stated my belief that the punct-substanz arose from a 
tnetHmorphosis 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 optic 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 Orangon. In reviewing this subject more 
carefully I am convinced that this interpretation is erroneous. These large clear cells are in 
reality undergoing indirect cell division, as proved by the karyokiuetic figures which are occa- 
AJoually seen. Both the chromatin network and the chromosomes are exceedingly delicate, and 
when ttie section is in the plane of the equatorial plate an api>earance is presented which udder 
cerlaiu ex>nditions of staining and preparation might easily be interpreted in favor of retrogressive 
metiiinorphosis. I conclude that the punct-substanz of the nervous centers is in all cases derived 
ttorn tLe protoplasm of cells, not from cell nuclei. 

In Stage IX 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, 
thii'kL'st 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 Palaemonetes 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 oesophagus behind the optic ganglion, where 
it is seen to rest against tbe yolk. The black pigment, though appearing to arise in connection 
with c<*rtain mesodermic cells (wandering cells from the yolk), it in reality belongs to deep ectoderm, 
and ni;Mks the retinular cells. The cell protoplasm bearing the pigment bodies grows outward 
(Fig. 14ii), and also i)ierces and extends some distance below the basement membrane (Figs. 191, 
IftlS). The latter is a delicate cuticular structure secreted by the ectoilerm cells which lie along 
the line of division of retina and ganglion, and continuous with the basement membrane of the 
hyi>odermis. In some sections it appears to be duplex, a condition described for the eye of 
the lobster by Parker (47), in which tbe inner layer enfolds tbe optic ganglion. Tbe wide open 
fissure which now exists between retina and ganglion (seen in transverse section at an, Fig. 136) 
is partially filled with yolk. Tbere 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. I think, however, that it can be stated definitely that none of these 
celts enti^r the retinogen. Tbey 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 difl:erentiated, or at least the pigment which these bodies give rise to, is seen 

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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 balk, 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), and 
finally 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. Bach 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 retinulae and to the acces;jory pigment cells. In deeper section, Fig. 191, 
we distinguish the proximal retinulae — 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 {rtl^). At the 
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 retinulse. Between this and the inn^r 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 occur 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 coute cells taper gradu- 
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 retinulae 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 two single nuclei. The two odd nuclei i>ertain 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 '*Coihparative 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 btaten 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 Paltemonetes. 

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454 MEMOIHS OF THK NATIONAL ACADEMY OF SCIENCES. 

The proliferating areas in the optic disks of Alpheus and Uoinarus ate uudoubtedly homologoaR, 
ami pmbably correspond also to the optic invaginations described in Astacns by Reichenbach and 
in Crtingon hv Kinp^sley. I therefore agree with Parker (47) in interpreting the ingrowth orinvo- 
lutifiij of *^(*t*Kleiin, whichever may occur in the developing disk, as concerned with the optic gan- 
gliun solely auil not with the retina. Beichenbach describes the visual organs as originating from 
three fuctorH: (1) an epidermal layer; (2) the optic invagination; (3) the optic or segmental 
gan^^tioii. From the epidermal layer an^ outer wall of the optic invagination the retina arises, 
white the inner wall of the secondary invagination unites with the optic ganglion. An inspection 
of Ueiciienbfiob's Fig. 224 (54) shows, as Parker has pointed out, that in all probability Beichen- 
bai;b has tnisinterpreted his sections, and that the entire retina is derived from the hypodermal 
layer* The layer of cells with elongated nuclei, which he has designated as rhabdom, clearly per- 
taiUK TO the optic ganglion, and probably represents the nuclear covering of the distal convex 
siirfiiee of the lame ganglionaire (Fig. 192 of this work). 

Kiiigsley, in his third paper on Crangon, changes his interpretation of the invagination of the 
optic di^k of Crangon, regarding this involution as concerned only with the optic ganglion. I am 
irjcUried 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 ha;^ 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 
segtiieutal value and are not merely outgrowths from the brain, that the eyestalk is a modified 
appendage containing its proper ganglia. 

Wataae^s interesting views (63) concerning the origin of the ommatidinm from a hypodermal 
pit do not receive the support we should expect from embryology. How much value is to be given 
to the etiibryological 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 tiace of similar iufoldings 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, 

THK KYE UNDER THE INFLUENCE OF LIGHT AND DAKKNE88. 

In Jane^ 1890, while enjoying the facilities for biological research afforded by the labora- 
tory of the U. S. Fish Commission at Woods Holl, Mass., it occurred to me that some valuable 
experimoot^ (Xiuld 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 
exp^'rimentw upon one form I learned of the experimental work of Exner* upon the eyes of the 
glowworm, Lmnpyris aplendidula, of Hydrophilus, Dysticus, and Colymbetes, in which he records 
the same plieuomenon in insects which I have observed in a Crustacean. Later a paper has also 
ajipeared, liy Mademoiselle M. Stephanowska, on the histological arrangement of ])igment 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, Pahttiwnetes 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 stieam of sea water could be kept run- 
ning throtigli it for any length of time. Three egg-bearing females were then placed in the 
iK]usiriiim and the chamber was sealed. The e^gg embryos were early nauplius stages. Females 
with eggs in a similar stage were also kept under observation in an aquarium exposed to the light. 
Tbe general cast of color of the prawn taken in the light is some shade of light brown or brownish 
greeiu Aftir spending eighteen days in the dark, the prawns were taken out and exposed to tlie 
moderately bright light of the laboratory. The eyes were jet black and appeared to have greatly 



'* fiiDoe tliti»e not«8 ^rere written I have received the completed work of Exner, Bie Phyaiologie der Faoettirien 
Augtn FOM Ertbt^u und Insecteny iu which the field of experiment in 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 theses was 
caused by the forward extension of the distal retinular cellSy of which there is a single pair in each 
ommatidium. 

The eggs of some of the prawns were hatching, and the pigment of the zoea was carefully 
compared with that of the Urst larva of Palaemonetes 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 t)ie 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 
retinulse 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 
retreat until, in the course of three-quatters of an hour, the distal retinul^ 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 Palsemonetes, 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 retinular cells thus sur- 
round the proximal ends of the cone cells. 

In the eye exiK)sed for thirty-eight days in the dark the distal retinular ceils 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 
cornea, and occasionally a cell shows a slight inward prolongation. Had the oyes 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 noti<5e 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-ix 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. 

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M€tQmo)*pho9is. — (1) The majority of the Alpbei hatch bh zoealike larvae, while two species are 
known^ AAfterochelis aud A. sauleyij in which the metamorphosiH in abbreviated. This shortening 
of f lie rrM'tsiniorphosis appears to be directly related to the habits and environment of the species. 
A. hnUmK'heliH has one metamorphosis at. Beanfort, North (Carolina, a more abbreviated develop- 
> in**nt ar Key West, Florida, and, if we are right in considering the Bahaman form as a member of 

I ' t\\\^ species, at Nassau, New Providence, the metamorphosis is complete or unabbreviated. The 

i NasMim foiiii q{ Alpheus saulcyi either has the metamorphosis greatly abridged or it hatches with 

all the external characters and the instincts of the adult. When we inquire into the modes 
o( litV of these species we find the remarkable fact that the Nassau Alpheus aaulcyi is a parasite or 
ciirttirioiisul, 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 
nM^tiunorphosis greatly abridged. The Beaufort heterochelu^ which must be regarded as descended 
frodiihi^ Floridian stock, has its metamorphovsis less abridged than in the latter case and it is 
ntiiif^anisnii*. However, we still find it occjisionally producing small eggs, indicating a tendency 
tu revt*rr to tlie old metamorphosis, long since abandoned. Even if we decide that the Nassau 
hvtefrpchelu has had a different genealogy from that of the Beaufort variety, we still have strong 
evhleiK'e nr show that the metamorphosis of the species may change in accordance with a change 
in liabits and environment. 

Varwtifm and Habits. — (2) Alpheus heterochelvt of Beaufort presents an interesting variation 
ifi the >;trtiL*ture of the small chela, which appears to be a sexual one. 

ili\ In many Macroura as well as Brachyoura, and especially in the Alpheus, one of the claws 
is eiiortiiunsiy enlarged, often nearly equal in size to the rest of the body of the animal. This great 
cliela may be either on the right or left «ide 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 
iuherired from the parents, and that where both of the latter have the right or left claw enlarged 
they give rise to right and left handed broods, respectively. 

(^) Alpheus saulcyi presents very profound variations, and some of these varieties would 
ijiidoabtedly be regarded as distinct species by systematic zoologists if the intermediat^e forms 
were unkiuiwn. These forms are described and discussed in Sections v and vii of Part First. 

HjR^cies 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 
ro a single 8|)ecies. Two well-marked varieties occur, which I have distinguished as Alpheus 
sanloyi^ vav. brevicarpus^ and A. saulcyi, var. Jongicarpus. Between these forms every intermediate 
stage m foiiui]. 

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- 
natoil it iM likely that this species would soon become separated into at least two distinct forms. 

it tseeujs most probable that the change in habits or environment which this species has under 
gone, has acted as a direct stimulus to variation. 



Structure of the Larva of Alpheus saulcyi. — (3) The structure of the first larva of this Alpheus 
reiit:heM a vt^ry high degree of complexity, which is but little exceeded by that of the mature adult 
tbnij. 

Tht^ green gland does not yet 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 ciiiHfer of large cells on either side of the middle line, between the digestive tract and the 
anterii^r end of the heart. For the histological details, reference must be made to Section i oi 
Pjut 8ee(Mi(L 

The Ovary and Ovarian Egg, — (0) The ovary consists of an external stroma of muscular and 
eoiitiective tissue and a lining epithelium. The ova arise from the lining epithelium, and each egg 



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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 (Agg membrane is the direct 
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 obscured and the germinal epithelium 
extends inward from the wall, in the form of radial sheets or folds, between which are reentrant 
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. 
In the germogen the cell outlines are obscured.* 

(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 
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. 

(9) I 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 
degenerate in the ovary, I find that the nucleus is at the suri'ace. It has the appearance of a 
female pronucleus. It is thus probable that the polar bodies are often, if not always, given off 
before the eggs are laid, t 

Segmentation in Alpheus minor.— r( 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 
present sufficient to enable me to say in exactly what way the usual process of cell division has 
here been modified. 

Belamination. — (11) The segmentation has been thoroughly reviewed in Section v, 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 blastodermic cells <1elaminate and their 
products pass into the yolk. In Alpheus saulcyi 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 
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 in 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 i)late, 
after all trace of the superficial pit has disappeared. 

Oei'm-layers. — (13) These migrating cells, which are collectively called *'tlie wandering cells" 
in Section vii, 8prea4l to all parts of the egg. While it is perfectly obvious that these bcnlies 
represent mesodermic and endodermic tissues, it is not so easy to determine what particuiar cells 
give rise to this or that layer, nor is it easy to decide 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- 

*The Btrooture of the ovary of the lobster has been recently described by Bumpus in a detailed paper upon the 
embryology of this species. He has called attention to the folded character of the ovarian epitholiuin, which is so 
marked in the young or immature ovary. (The Embryology of the American Lobster, by Hernion Carey Bumpus, 
Jovm. of Morphology, Vol. v, No. 2, 1891.) 

t Polar bodies have been recently described in the external eggs of the lobster by Bumpus. Op. cit. 



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458 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 

jei-t 18 fully considered in Section vii, the general results being : (1) That it is not possible to 
det^itle wliat part the primary yolk cells play in Alpheus, for reasons which have been already 
coiisifkretl ^^ (2) that the great bulk of the cells which migrate forward from the area of invagina- 
tiofi and attach themselves to the embryo, or proceed to the peripheral parts of the egg and take 
up a pomtJoii at the surface, are undoubted mesoblastic elements; (3) that those cells which give 
rise to the endodermal epithelium in the egg nauplius are derived largely from cells which migrate 
iit u i^osttfrior direction from the area of invagination ; (4) that degeneration, followed by the death 
and dissolDtton of the chromatin and cell protoplasm, is characteristic of the wandering cells at 
about the beginning of the egg-nanplius period. The mesoblast has become a well-recognized 
layer before the endodermal epithelium has appeared. 

(14) Thi^ i^ggy with centrally moving cells which have budded from the blastoderm, may be 
compared with the planula stage of Goelenterates, and the internal cells may represent the primi- 
tive eniloiii'riii. According to this view, the invagination stage has no reference to an adult 
gagtruEa^ike ancestor, but is a purely secondary condition, which became so impressed upon the 
anceistots of the present Decapods that it has remained in their ontogeny. 

lu the majority of Decapods which have been studied the invagination has no direct relation 
to the momtb or anus, or to the alimentary tract. The conditions which are present in the cray- 
fish cannot be regarded as typical or primitive. 

(15) 111 Alpheus and Homarus the primitive mouth arises on a line between the rudiments of 
the first pair of antennae, but these appendages are never post-oral. The hind gut originates as a 
nearly .^^olid ingrowth, apparently at a point considerably behind the position of the pit due to the 
first itivaj^'iti^ition, and is formed one or two days later than the mouth. 

Cell dumlution, — (16) The degeneration of embryonic cells is treated at length in Section vi. 
It is remarkable that the early segmentation stages oi 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 eventnally enter into the general nutrition. 

(17) Degeoerating cells appear in greatest force in Alpheus, Astacus, and Homarus at about 
the egg'UHuplius stage, and from that time their numbers begin to wane. They appear in one 
instance betbre the differenfiation 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 
r«?present mt/soderm and endoderm. The "secondary mesoderm cells " and " white-yolk elements^ 
which have been described by Eeichenbach, are to be regarded as degenerating cells. Degenera- 
ting cells al8o occur in connection with the "dorsal plate." 

The Et/eH,—(iS) The details of the structure and development of the eyes and nervous system 
are fully reviewed in Sections vtii and ix. 

The eyes^ and optic glanglia are derived from the optic disk, in the formation of which there is 
in Alpheus no proper invagination. The thickening of the disk is accomplished by emigration 
front the surface and by the delamination of superficial cells. An area of active cell division can be 
dii^itinji^tiiBlieil, which corresponds to the invaginate area of the optic disk of the crayfish. 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 
gajiglionic layer. The eye proper is differentiated from the retinogen, which is primitively a single 
layer of e^jtodermic cells. 

(19) I am inclined to regard the "compound eye" not as an aggregate of simple eyes, as its 
name imtilii s, 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. 

(2U) Tht^ absence of light has no appreciable effect on the development of the eye pigment, 
but ID Fakcmonetes the distal retinular cells respond very promptly to the action of light. If the 
light is extihaled 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. 

ADELBbUT College, 



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MEMOIES OF THE NATIONAL ACADEMY OP SCIENCES. 459 

XI.— BEPEBBNOES. 

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2. . Beport of the Present State of our Knowledge of the Crastaoea. RepU of 50th, Meet, of Brit, Aeg,, pp. 

230-241. 1880. 

3. . Beport on the Scientific Besnlts of the Voyage of H, M, 8, Challenger during the years 1873-1876. 

Zoology y Vol. XXIV. Text and separate volume of Plates. Beport on the Crvstazea Maorura dredged hy 
H, M, S. Challenger during the years 1873-1876, pp. i-xc, 1-942. 76 figures and 157 plates. 1888. 

4. Boas, J. E. V. Kleinere carcinologische Mittheilnngen. Ueber den ungleichen EntwickluDgsgang der Salzwasser- 

und der SUsswasser-Form von Palceinonetes varians, Zool, Jahrb,, Bd. 4, H. 4, pp. 793-805. Taf. xxiii, 
Holzsohn. 1-4. 1889. 

5. BOBRSTZKY, N. Zur Embryologie des Oniscus mnrarius. Zeit,f, wise, Zool. Bd. xxiv, pp. 179-203. Taf. xxi, 

XXII. April, 1874. 

6. . Development of Astaons and PalsBmou. Kiew, 1873. Abst. by Hoyer in Hoffmann and Hchwalhe^s Jahres- 

beriohU, Bd. n, pp. 312-318. 1875. 

7. Brooks, W. K. The Metamorposis of Alpheus. Jdhm Hopkins University Circulars, No. 17. 1882. 

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9. . A preliminary abstract of researches by W. K. Brooks and F. H. Herriok on the Life History of Steuopus. 

Johns Hopkins University CiroularSj Vol. viii, No. 70. 

10. Bruck, Adam Todd. Observations on the Embryology of Insects and Arachnids, pp. 1-31-f-lO, Pis. i-vi. Memo- 

rial Volume, Johns Hopkins University, Baltimore, 1887. 

11. BuLLAR, J. F. On the Development of Parasitic Xsopoda. Phil. Trans, Boy, Soc, Vol. CLXix, pp. 505-561, Pis. 

XLV-XLVII. 1878. 

12. Glaus, C. Untersuchungen liber die Organisation u. Entwickelung von Branchipns und Artemia, nebst ver- 

gleichenden Bemerkungen iiber andere Phyllopoden. Arbeit. Zool, Inst, Wien, Tom. vi, Heft 3, pp. 
267-370, Taf. i-xn. 1886. 

13. DiBTL, M. J. Untersuchungen tlber die Organisation des Gehims wirbelloser Thiere. ii Abth. (Crnstaoeen), pp. 

1-20, I Taf. Sittb. der k, Akad, der Wissensch,, Bd Lxxvii, i Abth. 1878. 

14. DouRN, Anton. Untersuchungen fiber Ban und Entwicklung der Arthropodeu. Zweites Heft, Zur Entwick- 

lungsgeschichte der Panzerkrebse (Decapoda Loricata), pp. 105-128, Taf. x. Leipzig, 1870. 

15. Erdl, M. p. Entwicklung des Hummereies von den ersten Veranderougen im Dotter an bis zur Reife des 

Embryo, pp. i-x, 11-40, Taf. i-iv. Munchen, 1843. 

16. Faxon, Walter. On some Young Stages in the Development of Hippa, Porcellana, and Pinnixa. Bull, Mus. 

Comp, Zool,, VoL v, No. 11, pp. 253-268, PU. i-v. 1879. • 

17. . On the Development of Palcemonetes vulgaris. Bull. Mus, Comp, Zool., Vol. v, pp. 303-330, Pis. i-iv. 1879. 

18. GUBRIN, M. F. E. M^NBYILLK. Aoimaux articul^s k Pieds articul^s, in Histoire Physique, Politiqueyet Naturelle de 

VHe de Cuba, by Bamon de la Sagra. 

19. Hbathcotb, F. 6. The Early Development of Julus terrestris. Studies Morph. LaVy Univ. Cambridge, Vol. ii, 

Pt. I, pp. 219-240, Pis. XXII-XXIIL 1884. 

20. Hbrrick, F. H. Notes on the Embryology of Alpheus and other ^^rustaeea, and on the Development of the 

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21. . The Development of the Compound Eye of Alpheus. Zool. Anz., No. 303, Figs. 1-5. 1889. 

22. . The Abbreviated Metamorphosis of Alpheus and its Eelation to the Conditions of Life. Johns Hopkins 

University Circulars, Vol. vii. No. 63, pp. 34-35. 1888. In the same number are Notes on the '* Habits 
and Color Variations '' and on the *^ Development of Alpheus." 

23. . The Beproductive Organs and Early Stages of Development of the American Lobster. Johns Hopkins 

University Circulars, Vol. X, No. 88, pp. 98-101. See also No. 80 of Johns Hopkins University Circulars, 
1890, and Zool, Am., Nos. 361, 362. 1891. 

24. Hkidbr, K. Die Embryonalentwicklung von Hydrophilus pioeus L. Erster Theil. Jena, 1889, pp. 1-98, Taf. 

I-XIII. 

25. HoWBLL, W. H. The Life-History of the formed Elements of the Blood, especially the red blood Corpuscles. 

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31. . The Development of Crangon Vulgaris. Second paper. Bull, Essex Inst,,Yol, xvm, Nos. 7-9, pp. 99-153, 

Pis. i-u. Salem, July, 1886. 



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400 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 

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XX XI -XXXIII. 1879. 
tU. J iKnifmN&Ki f <T. ICmige UnterHucbaDgen iiber die EntwickluDgsgeschichte der S**ekrablM»a. IHoL t'etkt^hll.^ B. X, 

Noft. » imd 6, pp. 178-186. 1890. 
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xnt-x-^. 1877. 
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21-21^, Fiiis. 1-8. v Jahrg. 18S2. 
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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 461 

G2. . fiiodes histologiques et organ ologiques sur lea centres nerveux et lea organes des sens dee animanx 

articul^H. Cinquifeme M^nioire. I. LeCerveaudn Crinuefc {(Edipoda carnleacena ei Caloptenus iialicus). 
II. Oouiparaison du cerveau des crustac^s et des inBecten. III. Le cerveau et la niorphologie da 
squelette c^phaliqiie. Ann. des Sci. Nat., Zool. et Pal^ontol., T. iv., Nos. 1-3, viiSer., pp. 1-1*20, Pis. 
1-6. 1887. 

63. Watask, 8. On the Morphology of X\\e Compound Eyes of Arthropods. Studied fr. Biol. LaVy of the Johns Hop- 

kins University^ Vol. IV, pp. 287-:i34, 7 Pis. 1890. 

64. Waldkyer, W. Eierstock uud Ei. 

65. Wii^oN, Henry V. On the Breeding Seasons of Marine Animals in the Bahamas. Johns Hopkins Unif?er8i1y 

Circularsy Vol. viii. No. 70, p. 38. 

66. Wood- Mason. Stridulating Crustacea. Remarks of Mr. Wood-Mason at the November meeting of the Entomo- 

logical Society of London. Nature, Vol. xviii, p. 53. 1878. 

67. Wheeler, William M. The Embryology of Blatta Germanica and Doryphora Decemlineata. Am, Joum, Mor- 

phologyy Vol. in, No. 2, pp. 291-386, Pis. xv-xxi. 1889. 



APPENDIX I. 
THE LIFE HISTOBT OF STEN0PU8. 

Since this paper was written Chun has described (Die pelagische Thierwelt in grosseren Meere- 
steefen, Bibliotheca Zoologica, i, 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. iv, Fig, 6) with the Stenopus larva shown in Pis. ix and x of this 
memoir shows that Chun's Meiersia clavigna is undoubtedly a Stenopus larva, a little older than 
the one shown in PI. 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 from the oviducts. According to recent observations of Cano 
{Mittheil Zooh Stat NeapoU, ix, 1891; abstract in Joum, Roy. Mic. Soc.^ 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 Speuce Bate on 
the Challenger Macrura (Report on the Crustacea Macrura dredged by H. M. S. Challenger during 
the years 1873-'76, Zoology, Vol. xxiv, p. 209, PL xxx, 1888). The Challenger brought home 
only two specimens of Stenopus hispidus^ one from Kandavu, 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 Haau.'' It has 
been thought that Squilla greenlandica of Seba, which ai>pears under several names, may be the 
same as Stenopus hispidus. "The genus,'' says Bate, ''thus appears to inhabit regions so widely 
apart as Greenland in the north, the Bermudas and Mediterranean in the west, and the southern 
coasts of India and the Fiji Islands 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 conclusion that the Arctic form is a Stenopus may be correct, it seems highly im- 
probable that it is specifically related to Stenopus hispidus. There is no evidence at lenst 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 family Stenopidae). This is clearly not a zoea, but Skprotozoea^ 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 the protozoea of Stenopus hispidus is very striking' (compare with PI. vii, 
Fig. 11, of this paper). 

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462 MEMOIRS OP THE NATIONAL ACADEMY OF 8CIBN0BS. 

Accord iBg to Bate the branchial formula of Stenopus waa first elacidated by Haxley in his 
memoir on the i^lassification of crayfishes (Proc. Zool. Soc., London, 1878). There are six plearo- 
brauchiie; eleven arthrobranchise, five of which are anterior and six posterior; one podobranchia, 
and M(T to asti^o branchiae, of which the first is the only efficient appendage. 

8}uiiice Hiite states that after careful comparisons he failed to find specific differences between 
fipecimeiid from the Eastern and Western Hemispheres. 

ERRATA. 

A«t iHitnei tms errors have unavoidably occurred in this paper, I will correct the more important 
of them, 

Pftjfe MX, litjt^ H, for ** PI. VII " read PI. x. 

Pnge 341, liDi> 13, for *' Lesneur" read Lesueur. 

I 'ago :U3, liDP 2y for *^ cells have spread more rapjdly at a given point on the egg'' read cells have increased more 
rHEiitlly over a givf n area of the egg. 

P»^6 343, ovi r table for "Temperature 80^ F.," read Temperature of air.SOo F. 

PilJ;*^ 341, lim ,s 11, 16, 31, 32, and 47, for " Fig. 10" read Fig. 11. 

Pai^o IM4, litu: 18, for " largely developed" read highly developed. 

PiiLge* 345, liiitj IM, for "Fig. 10" read Fig. 11. 

Pagft 345, line m, for "Fig. 11" read Fig. 10. 

Pagi) :i4rj^ litte ^» for " the first and second maxillipeds" read the second and third maxillipeds. 

Pagt^ 340, line 31, for " larger than telson " read longer than telson. 

Page 347, lino 16, for "xii and Fig. 40" read xiii and Fig. 39. 

Pagt^ 'M7t linL^ 29, for "and 38" read'and 39. 

Pag<i 347, lini s 37 and 41, for " PI. xi" read PI. xii. 

Page 347, \\n(^ 40, for '* Figs. 43, 45" read Figs. 43, 44. 

Page 347, liiu^ 47, for "Fig. 47" read Fig. 46. 

Pagw 348, It 11*^ 15, omit "errinem larve." 

Pagi^^dS, for lines 32-34 read: Body nearly cylindrical; tergal surface covered with spines. Carapace with 
urnmhj**iit lati^rally compressed rostrum and distinct cervical and hranchio-cardiac grooves. Outer antennae with 
loDg briBtlt^'boTih red scale bent under the inner antennie toward the middle line. Second maxillipeds with setig- 
ormiH Lunitia, attac:hed to endopodite. 

Pagu 348, Una 46, for '* a marked transverse fossa" read a marked cervical groove. 

Page 348, last litje, for " transverse furrow " read cervical or mandibular groove. 

rtkgo :M0, liuH 17, for " Fig. 40" read Fig. 39. 

Pago :UB, lim? til, for " their inner borders which meet in the middle line" read the inner borders of the exopo- 
ditee ^vliicb iiu*^t in front. 

P^gi^ ;M1), liisv ^, for " Fig. 39" read Fig. 38. 

Page 340, linf^ ^35, for " Fig. 38" read Fig. .36. 

Parjje 34^J, \iii<' 39, for " Fig. 48" read Fig. 45. 

F'dji^e M^, Bi'^ ' Qth line from bottom, for " the great chelae " read bearing the great chelie. 

Prtiie 3ri(i, tUsl hue, for " Fig. 48" read Fig. 47. 

Pag<^ 'Xd>^ iVr^^t und second lines, for '* bearing a shorter proximal one below" read bearing a longer tooth and a 
flhurtor proTtimat one below. 

Pagi> 3r.O, line 9, for "' Fig. 41 " read Fig. 40. 

Pa^ic 3ri0, laHk, tenth liue from bottom, for " Length of chela" read Length of chela of same. 

Patft^ 3r>2, litit^ 10, for " hartschalig " read hertschalig. ^ 

Page 'Xt2j ti^aUi line from bottom, for "Crustaces, Arachnidses" read Crustac^, Araohnides. 



APPENDIX II. 
PAEASinC FUNGUS IK THE EOG EMBBT08 OF ALPHEUS SAULCTI. 

The remarkable parasite of Alpheus saulcyi^ to which allusion was made in Part First of the 
Meiooir on the. development of Alphens, is illustrated in Fig. 199, PL Liii. Although a large num- 
ber of egg -befl ring 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 couditioos, ^ 

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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 463 

The sections of these enibrjos 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 literatnre, althoogh 
it appears to be a fungus belonging to Chytridiaceae. 

The fungus has no mycelium, but is composed of single cells of various sizes. In a section 
like that^hown 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 (c. «., Fig. 199) is a thick shell which has collapsed and curled 
up with the escape 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 encysted cells contain a protoplasmic reticulum (c«*), 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 rise 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- 
bryonic cells which have undergone modification. Occasionally one of tte cysts appears black 
(c«*), which is due mostly, if not wholly, to refraction. 

According to Goebel, reproduction in the Ohytridiece 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 Ohytridiece are described as parasites on other 
aquatic plants, Fungi, Algae, and Phanerogams. 

According to De Bary resting spores are known to occur in certain specieeC. 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. 

Adelbebt College, 

Cleveland, Ohio, May, 1892. 



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464 



MBHOIHb OF THE NATIONAL ACADEMY OF SCIENCES. 



I*LATE T. 
AiphfiuM mimr, ilmwti frrun liiu by W, K, I^rooka. (Enlarged eigrht diamet^rft.) 
Dorsal vi^nv ofn .^(leeimcfi nf the gray \ :inet.v of GoiwdcLctylm chiragraj twice natural size. 



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Plaiel. 




W.K.Bro6ks,dU. 



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ALPHEUS MINUS AND GONODACTYLUS CHIRAGRA. 



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S. Mis. 94 30 



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466 XBHOIHS OF THE NaTIOKAL ACADEMY OF SOIENGBS. 



Plate IL 
Alpheu^ het€rovhelut^ ilrawu from life b}" W. K. Brooks* (Four times life-ace.) 



h. 



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468 MHMoii;8 (>!■ ihb national academy of sciences. 



. Plate III. 
Oofiodactylus chiragray dmwn by W. K. Brooks. 
Ailult fBtoak' t^f tIk^ ^n. rri \ ariety, in her burrow, with eggs, twice natural size. 



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Memoirs Natiooal Academy of Sciences, 1889. 



PUKTE III. 




Ii; K.nnmks.iM. 



QONODACTYLUS CHIRA6RA. 



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470 



MBHOIBS OF THE KATIONAL ACADEMY OF SGIENOBS. 



/ 



Plate IV.. 
AcliiTt male mid fetnal^of jifpA^w* mulcyij var. brevicarpusy from Nassan, New Providence. 

Fio* 1. Lateral view of female from ^reen sponge. x3J. 

Fia, 2. Dorsal view of the same^ x3J. Parts only of the ovaries ar^ visible in Fig. 2, while the 
eggfi^ which greatly drnteud the abdomen laterally, show plainly between the bases of 
the swimmer^ts* Jn Fig. 1 the small chela is bent downward, the position in which 
it is umtally carried. In Fig. 2 the chelse are represented jn the attitude of defense. 
The dactyle of the left ^* band," or large chela, is raised preparatory to striking. 

PlG« 3. SmaU male. L ^ || in. x 7 j< Prawn under slight pressure, owing to which the antennal 
fipiues and the anteunulnr exopodites have assumed an unnatural position. The pos- 
terior margin of the carapace is more correctly represented in Fig. 1. 



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Pt€Ue IV. 




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ALPHEUS fiAlimvi \/AD BDe%/i/«ABBii< 



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472 



MKMOlKt^ or TUE NAT102JAL ACADEMY OF SCIENCEa 



Plate V. 

DoFRal Tiew of tlie adntt male ^Stenopus hispidus, Nassau, N. P., Jane, 1887. L=:l| in. L. first 
auteuDa, esoptKlite— 3J in., endopodite— 3| in. L. second antenna = 4|i in. x If. 

Excepting ttie brilliant pigtnent bands tbe body and appendages are nearly white, and could be 
better nprcsemed against a black background. The arching flagelhi of the antennae 
are greatly f'ore.sliortened, and the spines and setaB are of necessity andaly empha- 
flized in a pen ami ink drawing. 



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474 



HEHOIKS OF THE NATIONAL ACADEMY OF SOIENOEa 



Plate VI. 



Fto. 1. 



i 



Fig- 3* 
Fig. 3, 
Fig. 4, 

Fm, 5. 
Fig, ih 



Fig. 7. 
Fig, 8. 
FiG< a 



Part of eectiou of ^t^g^ showing the male pronucleus. The female pronucleus lies nearer 
ttit^ cf^nter of the egg, is Imti regular in outline iind has less perinuclear protoplasm. 
A Hiugle polar botly {not r^preaented) is seen in this section. It lies close to the sur- 
face of the iigg^ beiieatVi the membranes, not far from the male pronucleus. It appears 
»^ ?k ninall uiaes of chromatin, which stains quite as intensely as the nuclei. Egg 
about Ohonraold* x276. 

Sectlou of egg with four nuclei, none of which are at the surface, x 152. 

Part of same i*eetion, showing the naelens and surrounding protoplasm and yolk, x 276. 

Lfttf^ral section, cutting yolk BCf^mcntOQ. a level with the disk-shaped nucleus. Compare 
Fig. 5 a, Eight-ccU stage- Age about 12 hours. x276. 

3ectlon through egg in eight-cell titage. Compare Fig. 6. Age about 15 hours, x 152. 

Surface view of egg in tlie thiixi segmentation oreigfit-cell stage. The egg membranes 
have \yetm removed. The nuclei lie at a deeper level than they appear in the draw- 
ing. Compare Fig. 5, x 78. 

Section of ogg In the fourth segnientation stage. Sixteen cells, x 152. 

Fifth segmeij tuition atage. Age, 19 hours. Cells not yet at surface, x 152. 

Itivagioatiou stage. A solid ingrowth of blastodermic cells has taken place at Ig, where 
a alight pit is formed, Tlie set^^tion cuts obliquely through the in vaginate cells, x 152. 



REFEBENOE LETTERS. 

a, perinuolear protoplasm. 

Chj chittnouft eyrg envelopes (removed, ezoept in Fig. 5). 

Epf tictoblaiiio cell. 

Ig, iihanow pit of juvagination. 

f .. c » yolk sphi&rul«. 



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fi^-7. 



Figs. 




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STENOPUS HISPIOUS. 



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476 MEMOIRS OF THE NATIONAL ACADEMY OF SOIENCE& 



-5% 

Plate VII. 

Fig. 10. Left secotid maxilla of larva at the point of hatching, before the first molt, x 276. Com- 
pare with Figs. 26 and 21. 

FiO- 11. First swiinmiug larva, after the first molt, seen from below. Pigment cells, brown. 
_^ L= i^; in. (measarecl from tip of rostmm to median notch of telson). Length of 

rostra m = j^ in. x 70. 

Fm, 12. Eight firat masilla of first larva, seen from the oater side. Set® rudimentary. Compare 
Figs. 19, 25. x276. 

Fig, 13. TelsoQ of larva before first molt, seen from below. Compare Fig. 11. The setae are 
invaginated and covered with a loose cuticle. x276. 

Ft(f- 14. Eigbt first maxilliped of larva on the point of hatching, seen from the outer side. Setae 
invaginated. Compare Figs. 22. 25. x276. 

Fig. 15. Labrum and right mandible of larva, seen from above. x276. 

FiO. 16. Right third tnaxillipedof larvaon the point of hatching, seen from the outer side. Com- 
pare Fig, 25. x276. 

BEFEBENOE LETTEBS. 

A, oatermoBt spine in telson of larva at the point of hatching. 
4, equivalent of a in first locomotory larva. 
Lb, labrnm. 



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478 MEMoma of the nation al iAOademy of sgiengbs. 



Plate VIII. 

Fig. 17. Second larva after second molt. L=^o in. x70. 

Fig. is. Left maudible, outer side, of second larva. x276. 

Fig, 19. First maxilla of second larva, x 276. 

Fio. 20. Tel8on of second larva^ seen from below. x70. 

Fig. 21. Left second maxilla of second larva, seen from the outer side. x276. 

Fig. 22. Btgbt first maxllliped of seoond larva, seen from the cater side. x276. 

BBPaBBNOB ZJBTTXB8. 
, , , , tiie dotted line in Fig. 80 polnta to the outer ipine, the eqaiyftlent of d, Fig. 11. 



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PUiie VIII 




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STENOPUS HISPIOUS. 



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480 MEMOIilB OF THE NATIONAL ACADEMY OF SCIENCES. 






k^ 



Plate IX 

Advanced pelagic larva nf St^noptis hupfdusj from Beaufort, North Carolina, drawn from life by 
W, K, Brooke. 



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STENOPUS 



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S. MiB. 94 31 

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482 MBMOIBS OF THE NATIONAL ACADEMY OF 80IENCES. 



Plate X. 
Boraal view of a larva like the one shown in Plate IX, drawn from life by W. K. Brooks. 



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PlaA^X 




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W K.Bto6ks,dU. 



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484 MEMOIRS OF THE NATIONAL AGADBMT OP 80IBN0B8. 



Plate XI. 

Fi0. 25. Embryo nearly ready to hatch, released from the egg membranes, x 70. Some food 

yolk IS still uuabsorbed; swimming hairs very radimentary ; compare Fig. II. 
Fio- 26. Eight flrat antenna of older larva. x70. 
FiGt. 27. Profile view of hinder end of abdomen of same larva. x28. 
Fio. 28, Second maxilla of same larva. x276. 
Fig, 20. Mandible of same larva. x276. 
Fia. 30. First maxilla of same larva. x276. 
Fig. 31. Portion of third m^zilliped of same larva. x70. 
Fia 32. T^minal se^^ment of second pereiopod of same larva. x70. 
Fig. 33. First per«*ioiMKl of same larva. x70. 
Fig. 34. Portions of tbinl, lonrth, and rudimentary fifth ])ereiopods of same larva, x 70. 

BEFEBENGE LETTEB8. 

A, I, first antenna. • 

A, II f second antenna. 
Md.t mandible. 

ifxpd, I, Illy first and third maxillipeds. 
* B,, rostmm. 

Th., Th. 1, first maxiUiped. 

Th, ^Th, 5, third to fifth maxillipeds. 

1, first maxilliped. 



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Plate. XI 



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STENOPUS HISPIOUS. 



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486 MBMOIB9 OP THE NATIONAL AOADBMY OP 80IBN0B8. 



Plate XII. 

Tjg. 35* Older larva, taken in the tow-net oatside of Nassaa Harbor May 7, 1887, L=9"»™. L. 
of 6ye-atalk=s2'"°'. L. between eye8::=4.7°*°'. x 15. Tho long flagella of the antennae 
are cottTentionaUy represented to bring them into the plate. They trail above and 
behind the animal as it swims throng the water. 



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Plate XII. 




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F.H.Herri4j€.(Ul.. 



1 



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488 MEEdOIBS OF THE NATIONAX AOADEMY OF 80IEN0E& 



Plate XIH. 

Fig. 36, Firat maxilla, outer side. Adalt male, x 15. 

Fia. 37, Lateral view of carapace of adalt male. x5. 

Fig. 38. Left maadible, oater side. Adalt male, x 14. 

Fig. 39. Stalk ani portion of flagella of left first antenna, seen from above. Adult male. x5. 

Fig, 40. First right pleopod of male, outer side, x 14. 

FtG, 41. Left second antenna with flagellum cut off near its base. Adult male. Seen from 

above. x6. 
Fig. 42. Second maxilla of adult male, x 14. 
Fig. 43. Bight first maxilliped from outer side. . Adult male, x 14. 
Fig. 44. Bight secoDd maxilliped, from outer side. Adult male, x 14. 
FtG. 45. Bigbt third maxilliped, from under side. Adult male. x5. 
Fig. 46. Bight first pereiopod, under side. Adult male. x5. 
FiG< 47. Bight fifth pereiopod, under side. Adult male. x5. 



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PlcUe XIIL 



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Fi$.38. 




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STENOPUS HISPIDUS. 






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490 MEMOIES OF THE NATIONAL AOADBMY OF SCIBNOES. 



Plate XIV. 



M€tamorph<mg of OoTiodactylus ohirikgra^ drawn from life by W. K. Brooks. 

Fig. 1. Borsal view of egg Just before hatching. 

Fia* 2. Front view of the ftame egg. 

Fro. 3. Side view of the larva immediately after hatching. 

Fig* 4. Side view of the same larva after the first molt. 

Ftg- 5. Side view of the same larva after the second molt. 

Fig. i>. Dorsal view of the larva at the beginning of its pelagic life. 



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PLaU XIV 




iV K. limnks.deJ,. 



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GONODACTYLUS CHIRAGRA. 



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492 JidEMOIBS OF THE NATIONAL AOADBMY OF S0IEN0B8. 



Plate XV. 

Metamorpho9i$ of Oanadaotylus ohiragraj drawn from life by W. K. Brooks. 

Fta. T. Dorsal view of the larva shown in PI. xiy, Fig. 3. 

Fi&. 8, Ventral view of the same larva. 

Fm. 9. Dorsal view of the larva shown in PI. xcy. Fig. 4. 

Fig. 10. Ventral view of the larva shown in PI. xrv, Fig. 6. 

Fig. II. An older larva in dorsal view. 

Fig. 12. Same in ventral view. 

Fia. 13. Raptorial claw of a still older larva. 



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494 MEMOIRS OP THE NATIONAL ACADEMY OP S01EN0B8. 



Plate XVI. 

MetamarpkoHs o/AlpkeuSy drawn by W. K. Brooks and P. H. Herrick. 

Pia. 1. Third larval stage of Alpheus minor iTom below, drawn by W. K. Brooks. 

Pia. 2. Second larval stage ofAlpheus minoTj aboat one-tenth of an inch long, drawn from below 

by W. BL Brooks. 
Pia. 3. Telson of the Nassan form of Alpkeus heterochelis daring the second larval stage, drawn 

at 10 a. m., April 17, 1887, by P. H. Herrick. 
Pia. 4. Second antenna of Alphetu minor daring the first larval stage, from the inside drawn by 

W. E. Brooks, May 13, 1881, D. 2. (Zeiss lenses.) 
Pia. 5. Pirst and second maxillsB of the Nassaa form of Alpheus heteroehelis daring the foarth 

larval stage, drawn by W. E. Brooks from a sketch by P. H. Herrick. The larva at 

this stage is shown in PL xii. Pig. 3. 
Pia. 6. First maxilla of Alpheus minor daring the first larval stage, drawn at Beaafort, Jane 2, 

1881, by W. E. Brooks, D. 2. 
Pia. 7. Second maxilla of the same larva. 
Pia. 8. Mandible of the same larva. 



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496 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENOE& 



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Plate XVII. 
MetamorpJums o/Alpheusj drawn finom nature by W. EL Brooks. 

, Fio. 1. Side view of Alpheus minor after the second molt and in the third larval stage. Zeiss 

A. 2. This larva was about ninety-flve one-thonsandths of an inch long from the tip 

of the rostrum to the tip of the tcdson. 
FlQ. 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-hnndredths of an inch long. 
Fig. 3. Dorsal view of a yoang specimen of Alpheus heteroohelis 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 PI. xx. Figs. 2 and 3. . 



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498 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XVIIL 
* Metumorphosis of Alphetis^ drawn by W. K. Brooks from sketches by F. H. Herrick. 

Fig, 1< Side vi»*w of first or second larval stage of Alpheus heterochelvt from Nassaa, drawn on 

the iiigbt of April 15, 1887. Zeiss A. camera. 
FlGt 2, Yetitral view of the third larval stage of Alpheus heterochelis from Nassau, drawn April 

18, 1SS7. 
FiO< 3, Ventral view of fourth larval stage of Alpheus heterochelts from Nassau, drawn April' 

21, 1887. 
Fig. 4. Fii^t maxilliped of the first larval stage of Alpketis minor. 



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500 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XIX. 

Metamorphosis o/Alpheus heterochelis at Beaafort, North Carolina, drawn fh>m nature by W. K. 

Brooks. 

Fig. 1. Ventral view of the larva immediately after hatching. 

Fig. 2. Side view of the same larva. 

Fig. 3. Dorsal view of the autennale of the same larva. 

Fig. 4. Ventral view of the antenna of the same larva. 

Fig. 5. Mandible of the same larva. 

Fig. 6. First maxilla of the same larva. 

Fig. 7. Second maxilla of the same larva. 



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&02 MEMOlEti OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XX. 

MetamorphomB ofAlpheug heterockelis from Beaufort, North Carolina, drawn from natore by W. K. 

Brooks. 

Pig. L Embryo just before hatching. 

Fig. 2. View of a larv^* which was captared in the tow net at Old Topsail Inlet, North Carolina, 
June 25^ 1833* It is aboat eighteen one-handredths of an inch long, and is a little 
jonnger than tbe one shown in PI. xvii, Fig. 3, and a little older than that shown in 
Fig. 3 of thi« plate. 

J?iG» 3. Ventral view of a larva little younger than Fig. 2. 

Fio. 4. Telson and swimming appendages of the larva shown in Fig. 3. 

Fig. 5 First maxilla of tbe same larva. 

Fig. 0. Hecoiid maxilla of tbe same larva. 

Fl0. 7> First maxilliped of tbe game larva. 

Fig. W. Second maxilliped of the same larva. 

Fig. 9. Third maxilliped of the same larva. 

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504 MEMOIBS OF THE NATIONAL ACADEMY OP SCIBN0B8. 



Plate XXI. 

Fia. 1. ¥iTHt larva of Alphem mulcyi, var. hrevicarpus^ from ^^ loggerhead" aponge. Hatched at 

4 p, m*, June 10^ 1887. A small amount of unabsorbed food yolk remains in the 

8tomaeh, x26. 
Fig, la* Line to indicate length of larva. L.=3.5"«". 
Fig. 2. Second larva of same, from brood hatched on evening of June 8. Food yolk nearly 

absorbed. About twenty-four hours old. x26. 
Fig* 2a. Line to show length of larva. L.=4'""'. 
Fro. 3. Head of young from same brood. Four days old. x52. 
Fig, 4. Riglit fiiwt pereiopod of larva of A. satdcyij var. brevicarpuftj before the molt preparatory 

to stagfi ^4hown iu Fig. 1. Seen from inner side, x 52. Swimming hairs of exopodites 

rudiTTientary. 
Fig- 5, Egg embryo of A. saulcyiy var. longicarptM^ nearly ready to hatch. The large chela of the 

left first pereiopod is conspicuous below the antennae. x46. 
FiG- 5a. To show natural size of the same. Slightly too large. Dimensions: t^Xtotj i'^ch. 
Fig. 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. 

x227. 
Fig. 7. Left first pereiopod of same, seen from inner side. x52. 
Fig. 8. Third larva of Alpheus saulcyij var. brevicarpus. From same brood as second larva. Fig. 

2. Not over twenty-eight hours old. Food yolk not wholly absorbed. x26. 
Fig. 9. Telson and rudimentary uropods, seen from below. x52. 



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506 MEHOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXll. 

Fig. ]. Left sciconcl i>ereiopoil of first larva of A. mulcyiy var. brevicurputtj trom inside. x64. 

Fie. 2. Left third pereiopod of same, from inside. x64. 

Fig, 3, First nrnxillii of first larva of A. saulcyi from brown sponge. x2.55. 

FiG- 4. Left second ;ibdominal appendaj;e. of first larva of Alphefut saulcyi, var. brevic0/rpus, x64. 

Fia, 6. Left lirsit alulomiual appendage of the same. x04. 

Fig. 6. Eoijtrum of the same, seen from above, x ^>4. 

Fig. 7. Eight st^cMjnd antenna of the same, seen from below. x64. 

Fig. 8. Kight t^mt antenna of the same, seen from above. x<>4. 

Fig. 9, Se<?ond antenna of young of Alpheus sanlcyi^ var. breviearp^iusy six and a half days old. x 64. 

Fig. 10. First anteTitia of the same, x 64. 

Fig, 11. Head of male of Alpheus mulcyi^ var. tongicarpusj from ^'loggerhead" sponge. Median 

spine of rostrum wanting. Drawn from life. L.=5.5™"'. x3L 
Fig. 12. Mandible of first larva of A. saulcyi, var. brevicarpus. x255. 

Fig. 13. Left sticond antenna of male of A. saulcyi^ seen from below. No. 8 of Table I, p. 385. x33. 
Fitx. 14. I^eft second antenna of female of A. saulcyi. From No. 9 of Table I. x33. 
Fig. 15, 8m all clK-la of larva of A. naulcyiy var. brevicarpusy shown in Fig. 17, at time of hatching. 

Compare this with the same appendage of the adult. x64. 
Fig. lt>. Firrtt pt^reioi^od (small chela) of young of A. saulcyi^ var. brevicarpns, From^green sponge. 

Compare this with Fig. 3, PI. xxiv. x64. 
Fig, 17. Front of n larva of A. saulcyi, var. longicarpus^ which was hatched April 25. Drawn 

undt^r pressure ; eyes slightly distorted. Equivalent to the ordinarj'^ third larva, Fig. 

8, PL XXI. x64. 
Pig. 18. Part of ^talk of right first antenna of male of Alpheus saulcyi^ seen from below, showing 

the aiiial scale. The median eye is seen on the right, between the basal segments of 

the antennules. From No. 8 of Table I. x 26. 



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508 MEMOIBS OF THE NATIOI^AL AOADBMT OF S0IBN0B8. 



Plate XXIH. 

Fig, 1. Kif^ht (second pereiopod of male of Alphem sauleyij var. hrevioarpus^ seeo from the outer 

side- x33. 
Fig. 2, Terininal Hefj^ments of right fifth pereiopod of the Bame. x33. 
Fig. 3< Ijeft inau(li}>le of the same, seen from the outer side. x64. 
Tm, 4, Left fir^t antenna, and left compound eye of the same, seen from above. x33. 
Fia, 5, Left third Tnaxilliped of the same, seen from outer side. x33. 
Fig. 6. Kight ^coud raaxilliped of the same, seen from the outer side. x64. 
Fig. 7. Bight first tnaxilliped, seen from the outer side. x64. 
FlG> 8. Bight second antenna of the same, seen from above. x33. 



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510 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 



Plate XXIV. 

Fig. 1. Ri^bt fifth pereiopod of male of Alpheus saulcyi, van br&vicarputt^ seen from outer side. 

x33. 
Fig. 2. Small chela of male of A.saulcyij var. longica^rpus. From No. 9, Table I. x33. 
Fig. 3. Small chela of male of A. saul<yyij var. brevicarpua. From No. 8, Table I. Compare with 

the typical form of the other variety, shown in Fig. 2. x33. 
Fig. 4. First pleopod of male of A. mulcyi^ from "loggerhead'' sponge. x33. 
Fig. 5. Left first pleopod of female of A. gaulcyij from "loggerhead" sponge. A single egg is seen, 

attached to three hairs of the protopodite. The hairs are coated with glae, and the 

gluey threads are twisted into a chord, which is continuous with a thin sheet of. this 

substance (the membrane of attachment or secondary egg-membrane which envelopes 

the e^gg). Below is seen a single hair, from which an egg has broken loose. Drawn 

from an alcoholic specimen. x33. 
Fig. 6. Right second pleopod of larger female of A, saulcyi^ showing a number of eggs attached, 

seen from behind, x 14. 
Fig. 7. First maxilla of A. mulcyi. Endopodite bent out of position, to a point below the large 

coxopodite. x 04. 
Fig. 8. Large chela of female of A. saulcyi, from "loggerhead" sponge. Compare with the brevi- 

carpus shown in PI. iv. x33. 
Fig. 9. Right second maxilla of A, mulcyi j seen from outer side. x64. 



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512 MEM0IB8 OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXV. 

Fig. 1. Surface view of segmenting ^gg of Hippa talpoides. Thirty-two yolk pyramids present 
x38. 

Fig. 2. Embryo of Hippa talpoides^ showing optic disks and thoracic-abdominal plate. x38. 

Fig. 3. The central part of a transverse section of the ovary of the lobster, Homarus americanusy 
to show the progressive development of ovaj ftom the same series as that repre- 
sented, with less enlargement, in Fig. 0. Ovary taken in January. x28I. 

Fig. 4. Section of egg of Hippa talpoides in yolk segmentation. Sixty-four yolk pyramids pres- 
ent. X 70. 

Fig. 5. Part of segmenting egg of Alpheutf minor ^ showing a single large nucleus and two smaller 
nuclei. Compare with Fig. 23. x281. 

Fig. 6. 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. 

Fig. 7. Egg-nauplius embryo of Hippa talpoides. Appendages appear as simple buds. x38. 

Fig. 8. Post-nauplius stage of Hippa. Abdomen bilobed at tip. Buds of ac 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. 

Ah. P.f thoracic abdominal plate. 

B, C, blood cell. 

Bl. S,f blood ainuti. 

CA., chitiDoas eggshell. 

Ch. fT., limiting membrane of blood Binns. 

Ct. S., ovarian stroma. 

E, /,, egg follicle. 

^' ^j egg follicle. 

Ger.y germogenal area. 

/. E,f ovarian stroma (undifferentiated). 

0, o^-o'f nuclei of ovarian stroma and developing eggs. 

0. />., optic disk. 

0. L., optic lobe. 

T. P., yolk pyramid. . 

Y. 8,, yolk spherule. 

Vac., yolk vacuole. 



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514 MEMOIRS OF THii NATIONAL ACADEMY OF SCIENCES. 



Plate XXVI. 

Fia. 9. Section through segmenting egg of Alpheus ftaulcyi. Eight cells present. Yolk unseg- 
mented. Egg membranes diagramatically represented, x 70. 

Fig. 10. Surface view of the same. Sixteen cells present. Yolk pyramids formed. The periph- 
eral nuclei are seen through a thin layer of yolk. x70. 

Fig. 11. Transverse section through the immature ovaries of Alpheus. Ovary taken in June* 
from female '^ in berry." Diameter of largest ovarian eggj one one hundred and 
sixt3^-eighth of an inch. Diameter of extruded eggj one fiftieth of an inch. Contents 
of ovarian eggj one thirty-seventh of that of the extruded egg. x28L 

Fig. 12. Section through segmenting egg of Alphem minoTj from Be^ufort^ North Carolina, show- 
ing nests of nuclei, x 70. 

Fig. 13. Swarm or nest of nuclei, like those of preceding figure. x281. 

Fig. 14. Section through egg of Alpheus minor^ cutting segmentation nucleus. Nucleus elongated, 
with irregular, indefinite boundary, x 70. 

BEFEBENCE LETTERS. 

AU C.f alimeutary canal. 
B, C, blood cell. 

'B. S., blood space (possibly uonaturally distended). 
C^., cbitinous egg envelopes. 
D. A.J dorsal aorta. 
€, c', young ova. 
F. E.f ovarian stroma. 
F. E,\ follicular epitbelinui. 
h\ C, follicular epithelium. 
Ger.y geruiogeu. 

Ger^j position of germogeu iu ovary, with ova nearly ripe. 
Gr. F., germinal vesicle. 
0. W,, ovarian wall. 
SSy swarm of nuclear bodies. 
Vao.t yolk vacuole. 
Fit., vitellogen. 
X, cell shown in Fig. SO. 
Y, P., yolk pyramid. 



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516 ' MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXVII. 

Fig. 15. Section of t^gi^ of BabankHti variety of Alpheu/t Jieterochelis in typical yolk pyramid stage 
Sixty^ tour c**l Is prescii N x 70. 

Fig, 16, fsfgmeutation nin^leuH of *igg of A. saulcyij nearly central in position. x277. 

Fig. 17, Sec^tion of an t^g^ of .4. aaulcyi, which was normally laid bat unfertilized, showing the 
female pro[tuGleu.s. x70. , 

Fig. 18. Degenerating;: nnch^i (containing spore like bodies, from the egg-nauplius embryo^ the 
structure of which is j^ihown in Pis. xx.i-XLrn. x610. 

Fig- 19. BJood cells of adult Ali>btMis. x6I0. 

Fig. 20. Eudodermal colls froju tlie ventral wall of the primitive alimentary cavity of Astactis 
JiuviatUifi. After HiMihenbach (54) Taf. viii, Fig. 67. This is taken from the egg- 
jiaiiplius sLa^^e tu show the origin of *' secondary mesoderm." The elements here 
markml m\ k ;irt* dt^Ht:ribed as cells which have originated from the endoderm, and 
completed their met^nnorphosis into ordinary mesoderm cells. These maybe com- 
pared directly with b^ Fio. 18, and «, «*, Fig. 21, from the egg-nauplius of Alpheua 
amdcyi^ and are rat\}er to be regarded as nuclear bodies in tbe earlier stages of 
i retro^^remre meianjorphosis. x256. 

Fig, 21, Part of transverse seetion through the foregut of the egg-nauplius oi Alpheun saulcyi, to 
show the degenerative cell products. x610. 

BEFEBENGE LETTEBS. 

A. Y. S.f altered food-yolk. 
Ch,j chitiDOOs egg membranes. 
ec.f eet CI blast. 

i., uu^Ibiu: body, with vesicular chromatin mass. 
k, k\ 7, ntj m^-3, nuclear products in yolk. 
Jlf^.f DK^tiublaet. 

K.J N.^j nuclei of entoblastic cells, 
n,, Duulodlus of entoblastic cell (not clearly shown). 
Of,, oil drop. 

B^i.j protoplasmic reticulum. 
Sj ^f «%, degenerative products. 
Sap.^ cleav^age plane. 
Sid., fursgut. 
FtfCp, yolk vacuole. 
y., yoik. 

F, P,, Yi>lk pyramid. 
Y.S.f yolk sphere. 



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518 MEMOIRa OF THE NATIONAL ACADEMY OP SCIENCES. 



Platk XXVIII. 

Fig. 22- Part of section of aegnietiting egg of Alpheus minor from Beaufort, North Carolina, show- 
ing nuclear botly in clear area. x"217. 

Fig* 23. Swollen, iirobably tle^eiicrating, elements, from segmenting egg of J., minor. x277. 

Fig. :24, Section tliruugh base of yolk pyramid of egg of Paloenionetes vulgaris. About sixty-four 
cells prei*ent. x-77, 

Fias* 25, 26, Two ^uece^sive sections through clear area in segqaenting egg of Alpheus tntYior, 
!!iho\Tiug degenerative products and nuclear bodies in process of breaking up. x277. 

Fig. 27. Part of section through ^;egmenting egg of Pontonia domestica, before cleavage of the 
yolk. The egg contains three nuclei, one of which is seen to be in karyokinesis. 
X277. 

Fig. 28. Part of section of au Alpheus egg in same stage as that shown in Fig. 9. Cell dividing 
■ iDdireetly and in horizontal plane. x277. 

Fig. li9. Section of egg of AlphetiH minor ^ probably at close of segmentation. x277. 

Fig. 30, Enlari^^ed view of t^^ll 4\ and part of section shown in Fig. 9. x277. 

BEFEBENGE LETTEES. 

^A>, egg niembraneH. 
^ A",, nucleus. 

P. A.y protoplasmic area. 

/'. y., perinuclear protoplasm. 

Sf\ <SC'-*, degenerating cell products. 

1\ 5»olk. 

r. B., yolk ball. 

1 , a.f yolk sphere. 

Poc., vacuole. 



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520 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXIX. 

Fta. 31. Part of section of egg of BahamaD variety of Alpheus heterochelis^ showing two jolk 
pyramids. Same stage as Fig. 15. Sixty-four cells present. xli77. 

Fia, 32. Part of transverse section of egg-nauplias of A. saulcyij showing the fold of one of the 
antennae and the mesoblastic cells and degenarative products contained within it. 
x610. 

Fia> 33. Wandering cells in yolk above the same embryo, showing protoplasmic union. xOlO. 

Fig. 34, Part o'f section of egg of the Bahamau heterochelUt in egg-nanplius stage, showing wander- 
ing cells, which have left the yolk and bave attached themselves to the superficial 
ectoblast The nuclei are flattened against the surface, but are clearly distinguished 
from the epiblast. x 610. 

FtQ. 35* Part of transverse section of older embryo, showing blood cells and wandering mesoblast 
cell {Mes.). Eye-pigment beginning to form. x610. 

Fia. 36. Part of longitudinal section of embryo shown in Fig. 153, to show the degenerative prod- 
ucts of the dorsal plate. x610. 

REFERENCE LETTERS. 

App., app«ndaf2[e. ^ 

A.T,S.t altered yolk. 

B, C, blood corpuBcle. 

Ch,f egg membranes. 

C P., united psendopodia of two wandering cells. 

Eot., ectoblast. 

Ep.f spindle-shaped nuclei of surface epiblast. 

Me^.f Mes^f mesoblast. 

Mu.j muscle cells. 

Pn,^ cell protoplasm. 

Pl,^ coagulated blood. 

9, s^f d<|generative cell products. 

Sep.j inner wall of yolk pyramid. 

S, W,, outer wall of yolk pyramid. 

Y, C, wandering cells. 

Y, S.y yolk sphere. 

Fao., vacuole. 



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522 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXX. 

Fig. 37. Part of sect ion uf egg before iuvagiuatiou stage, showing primary yolk cells. All the 

iigures oii thi« plate, exceptiug Fig. 46, refer to the Bahaman form of Alphetu hetero- 

chdin, x27T, 
FtG- 3S-44. OoDsecntive sections of the sarae egg^ showing the progress of the primary yolk cells 

ill their migriition from the blastoderm to the central parts of the egg. x70. 
Fig. 45> Section through tJie same egg^ showing seinidiagrammatically the structure of the yolk. 

x7il 
Fio. 40. Section through the egg of A. ttaulcyi at a slightly later stage, but before invagination. 

The bTuHttMlenaic cells lie at the surfjace, the primary yolk cells toward the center of 

the egg* Tnu^es of the primary yolk cleavage are still seen at the surface, and a 

secondary cleavage has occurreil below the surface, x 70. 
FifK 47. Surfiioe view of the side of eggj corresponding to the germinal area in nearly the same 

*4ta^e, x70. 
Fm. 48p Tangential Meiaiou, showing blastodermic C/Clls of same Oigg. x377. 

REFERENCE LETTERS. 

/' 

Hy a'~^ cells migrating from lihiHtoiloriu into the yolkl 

lid. C, blastodermic cell. 

Ch.f eggshell. 

(r. D.J embryonic area. 

Sep.f yolk cleavage plaue. 

Y. B., yolk baU. 



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524 MKMUlittJ OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXXT. 

Fiaa. 4:9-55. Berial tratiRverse sectionn througk the embryo in the invagination stage. In the 
moHt aiiteriar aection the germinal area (O. 2>.) is traversed, and in Fig. 53 the shal- 
low depre»stou in the middle of the iuvaginate area is cut through. In Fig. 54 (Q» 
D.) we Hee the forward extension of the invagiuate cells and the first trace of the 
thoracic abdoDj in al plate. The distinction between the primary yolk cells (Figs. 49, 
52» 53-5o) and tbe invaginate wandering cells (6, 6*-*, Figs. 52-54) and their product, 
which now h^gw their migrations, is very plainly shown. In Fig. 50, which cuts 
the shallow pit i\t the surface of the invaginate area, we see the amoeboid cells with 
large granular luiclei making their way from the bottom of the pit into the depths 
of the yolk- Figs. 40, 52-55, x 115. Figs. 50, 51, x 291. 

REFERENCE LETTERS. 

bf b^b^^ in- wandering colls derived from the invaginate cells and their products. 
Ch*f 6gg captiule or ftbell. 
Ep., ei^tiibliMt. 
Q. D.^ embryoDtc area. 
/, C, invfiginatci cell. 
« Ig,, pit formal by the invai^ination. i 

r. B., yolk ball, 
F, r, C, primary yolk cell, 
f". S.^ yolk sphere. 



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526 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plati: XXXII. 

Kicif<. r>tj, 51t, (kK Lotigttiiiliual serial sections through the entire embryo iu the stage shown in Fig. 
^, Fig. -W is median. The primary yolk cells (P. Y, C, Fig. 60) can still be distin- 
gui^heil front the wandering cells derived from the invagination (8. Y, C, P'ig. 60). 
In Fig. 01) n primary yolk cell (P. F. C.^) is in the metakinetic stage of division. 
Trace*! of tli«^ primary segmentation of the yolk are still present, and the secondary 
yoik st^gmrn cation is very marked in the neighborhood of the wandering cells, 
t Where the sheU (Ch,) is not removed it is seen to be considerably* distended and to 

have epiblavstic cells sticking to it, showing the close adherence which normally exists 
between the i^gg membranes and the egg, xll/i. 

Fn;, r>7* Section through t^ggj cutting germinal disk just before invagination. Twenty and one- 
half hours older than yolk-pyramid stage seen in Fig. 15. x73. 

Fig* -'►H. 8arface view of embryo after the appearance of the thoracic-abdominal plate and the optic 
disks. The shallow depression which marked the invaginate area has disappeared. 
Its approximate position is indicai:«d by Ig. Compare Ig.y Fig.- 59. x291. 

» BEPKRENCE LETTERS. 

Jb. /\, vt^ut^ail plate. 

if, D., gerrulnal disk. 

/?., pit ot'invakfzination. 

L. Vd., lateral ventral bandH. 

O. D., optic dmK. 

p. M,, wandering cells, seen below surface, coming off from ventral plate. 

P, r, €., P. r. C.>, primary yolk cells. 

^S'ep., yolk oleavage plane. 

S, y, C.f S. V. C, \ wandering cells derived from the invaginate celU and their products. 

T, Cd.^ oetl area uniting optic disks. 

r. B., jolk bail. 

F. C, primary yolk cell. 



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528 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 

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Plate XXXIII. 

FiGB. 61^ 62, 68, 69. TransverBe sections of embryo iu stage shown in Fig. 58, PI. xxxii. Fig. 61 
cuts the thoracic-abdominal plate, and Figs. 68 and 69 involve the optic disks. Pri- 
mary yolk cells (P. Y. C. Fig. 69) are still plainly distinguishable. xll6. 

Fig. 03. Portion of median longitudinal section of the same stage. The larger and clearer nuclei 
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. x291. 

Figs. 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. x291. 

BEFEBENOE LBTTEB8. 

Ab, /'., veDtral plate. 

CKy eggshell. 

Ep.f botoderm. t 

Ig,j iDvaginate cavity. 

L, Cd. f lateral ventral cord. ^ 

0. D,, optic disk. 

P. y. C, primary yolk cells. 

Sep.f yolk cleavage plane. 

S. y. ' ., in-wandering cells derived from ventral plate. 

Y. B., yolk baU. 



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530 MEMOIRF OF THE NATIONAL ACADEMY OF SCIENCES. 



Platk XXXIV. 

(Stage IV.) 

Figs* 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 j^enerally indistinguishable from the other wandering cells. Compare cut, Fig. 
Ill which shows the distribution of the wandering cells at this stage, xllo. 

Fig. 73. Surface view of embryo in Stage iv. Rudiments of the mandibles and first pair of antennae 
are piesent. An area of cell ingrowth in the optic disks (C. M.) is characterized by 
the large size of the nuclei. From them and their products the optic ganglion takes 
it8 origin. Some of the surface cells on either side of the middle line were acciden- 
tally cut away. x291. 

REFERENCE LETTERS. 

• A. (I,), proliferating ceuter of firat autonna. 

Ab. P,, ventral plate. 
C. M,, proliferating area of optie disk. 
Ep.y ectoderm. 
L. Cd.y lateral ventral cord. 
Md.y proliferating center of mandible. 
0. Z>., optic disk. 

T. Cd.f transverRe cord uniting optic disks. 
F. B., yolk ball, 
r. C, r. C.\ wandering cells. 



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532 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXXV. 
(Stage IV.) 

Fig. 75. Median lougitudinal section of the entire embryo. One of the wandering cells, which is 
approaching the surface of the egg opposite the thoracic abdominal plate, is in the 
process of division, x 115. 

Figs. 76-83. Consecative serial transverse sections through the left optic disk of same, to illus- 
trate the earliest stages in the thickening of the disks. The most posterior section 
(Fig. 83) cuts the first pair of antennse. x291. 

Fig. 84. Transverse section through the middle of opUc disks, x 115. 

Fig. 85. Transverse section through thoracic abdominal plate, showing the multiplication of sur- 
face cells, by which the plate is increased, and celli^ below the surface (Y. C.) which 
.. pass into the yolk. x291. 

, BEFEBBNCE LETTERS. 

A, {1 ), first auteima. 

Ah. P., ventral plate. 

CA., eggshell. 

C. M.f proliferating area of optic disk. 

ec.^ ec.'~^ ectodermio cells of ventral plate (Fig. b5). ec., (Fig. 80) eotoderuiio cell of optic disk. 

Ep.^ ectoderm. 

O. D., O. 2)'., optic disks. 

Ret y protoplasmic reticulum. 

T. Cd.f transverse cord. 

r. B., yolk ball. 

¥. d., F. C.»^, wandering cells. 

F. S.y yolk spbere. 



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534 MEMOIKB OF THE NATIONAL ACADEMY OF SCIENCES. 



Platk XXXVI. 

(Stage V.) 

Figs. 86, 87, Parts of loDgitudlDal sections of embryo seven or eight hours older than that shown 
in Fig. 7l\ Tlie optic 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. x291. 

Figs, 88-89. Longitudinal ferial sections through the entire embryo, somewhat younger than the 
last, and nix hours older than that represented in Fig. 72. The optic disk is sectioned 
in Fig. 9^1 through its central proliferating area (0. 3f.), and the rudiments of the 
three naupliar appendages appear in Fig. 89. xll5. 

FiG. Ul. Transverse section cutting optic aisks of embryo about nineteen hours older than that of 
Fig. 72 and twelve hours older than that represented by Figs. 86, 87. Wandering 
e^llH ( y. G.^) have tniveled to remote parts of the surface, and karyokinetic figures 
( Y. C,\ Fig. 89) juine that they are in active division. xll5. 

REFERENCE LETTERS. 

A. (/), mdiment of tirst antenna. 

A. (//), rudiment of Hecond antenna. 

Ah. P., ventral plate. 

Jpp.y area of appendages. 

Ch., eggHhell. / . 

t\ M.f proliferating area of optic disk. 

rt^f migrating ectoblast cell. 

Ep., ectoderm. 

jVd.y rudiment of mandible. 

0. D.J optic disk. 

S.r product of degenerating chromatin. 
St. A.y sternal area. 
T. Cd.j transverse cord. 

1. C.J Y. C.^-^j wandering cella. 
r, S.J yolk sphere. 



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536 BIEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXXVIT. 
(SUges V-VI.) 

Fro, 02. Part of transverae ftectiou, showing the structure of the keel-shapeil ventral plate, and 
indicating the origin of mesoblast from the surface of the latter. x291. 

Ftg. 1>3. Sarface view of einbr> o with buds of naupliar appendages. The intermediate area {8t A.) 
is covered by a single layer of ectoderm. The invagination of the moGth has not 
yet a|)|)ear6d> Some nuclei of cells which lie immediately below the surface, especially 
in the thoracic aMominal plate region, are represented. x29l. 

Fl&s. 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 («.', ft,\ 
Fig» 95) are present, and twOTjells are seen delaminating side by side in Fig. 95. 

REFERENCE LETTERS. 

A^ (/), rndiment of first autenna. 
A. (//), rudiment of second antenna. 
Jb, P,j ventral plate. 
< r. i/., proliferating area of optic ganglion. 
Evt.^ (5c'toderm. 
Md.^ nidiroent of mkndible. 

Mefi.f wandering cells (mesoblast) attached to ectoderm. 
O. G.f rudiment of optic ganglion. 
0. D.f optic disk. 

l.^ it.'^j prodacts of degenerating chromatin. 
Sl A.J sternal area. 

T. Cd., transverse cord uniting optic disks. 
y. €., wandering cell; Y, C.\ wandering cell degenerating. 



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638 MKMOllUi OF THE NATIONAL ACADEMY OF SOIENCEd. 



Plate XXXVIII. 
(Stage VI.) 

Fi03. 96-97. LoDf^itiidliiid sections through the embryo shown in Fig. 93. The more lateral of the 
two, Fig. 94i, 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 
[jortioii of the optic disk and the ventral plate on a level with the budding mandible 
(Md-)* x295. 

FioB. 98-100. Lfongitudiual serial sections through an embryo six hours older, from the same 
batch of egp:s. The mouth (Fig. 98, 8td,) has already appeared. The meaoblast, 
formed chiefly from wandering cells, is well established on either side of the middle 
line of the l>ody, 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 if) still being increased by the migration of cells from the surface of this plate, 
;i8 i» indicated by cell ec.^ which is interpreted as a superficial cell about to migrate 
(in Fi^. 98). In Fig. 100 a cell at the surface of the optic disk is in the act of delami- 
natitij]^, [jarge numbers of degenerating cells and their products are now encountered 
{>». C, #.), k295. 

BEFBBENCE LETTERS. 

A. (i)i bud of first Antenna. 

.-r. (// ), bud of second antenna. 

Ab.j Ah. P., Ad. P., ventral plate. 

App.j area of appendages. 

€. M., proliferating area of optic disk. 

4W.i ec.\ migrating and dividing cells at tmrfaoe of ventral plate. 

Eot.f Ep,y ectoderm. 

Md., rudiment of mandible. 

M^M,, Tuesoderm. 

O. C, ijptic ganglion. 

O. D.^ Dptic disk. 

J)., fj^f prod acts of degenerating chromatin. 

S. C^j S. C.^-^y cells in various stages of degeneration. 

^1. J.^ dternal area. 

Sid.^ t^tomodwnm. 

T. Cd.t Transverse sheet of ectoderm uniting optic disks. 

r., r. S,y yolk spheres. 



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540 MEMOIRS OF THE NATIONAL ACADEMY OF SCIBNCBS. 

Plate XXXIX. 
(Sta^e VI.) 

Ftos. 101-105. Serial loDgitudinal sections of early nauplias embryo, twelve and one-half hoars 
oUli^r than that represented by Figs. 98-100, PI. xxrviii, and eighteen and one-half 
hours older than the stage represented in Fig. 93, PI. xxxvii. The thoraeicorabdomi- 
nal fold or papilla is now forming, apparently by the ingrowth of the sarface ectoblast 
(Fig. 104y Ab, C). Fig. 102 is exceptionally fa\^)rable in showing the andoabted 
delamination of two cells standing side by side at the sarface 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 ee.^ of the same section. Fig. 105 cuts 
the straight tabular stomodsBum. x 295. 

Fig* lOH* FjOu^ i tudinal median section of embryo several hours older than the last. A deep, narrow, 
tnussverse furrow (Ab. C.) now abruptly separates the thoracico-abdominal papilla 
from the sternal area lying between it and the stomodtenm. x291. 

Fro. 107. Transverse section through the optic disks, from same stage. Cell delamiuation in this 
region is again met with. x291. 

Fig. ids. Longitudinal lateral section through entire egg, showing the distribution of wandl^ring 
cell^, and the relations of the embryo to the ovum. The eggshell is unnaturally dis- 
te tided. An inner molted membrane is present, as is better shown in Fig. 106 and 
l^g. 104, Mb. 

In Fig. 108 a large cell is seen at the surface, and below this a large c^ll followed 
hy 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, x 115. 

REFERENCE LETTERS. 

A, (Pij bud of first autenua. 

A* (I()f bud of second antenna. 

Ah, J thoracico-abdominal papUla. 

Ab. C.f transverse superficial furrow by which fold of the thoracico-abdominal process is formed. 

A. y. S., products of degenerating chromatin. 

B. jr., budding zone. 
Ch.f t^ggshell. 

C JLf.^ proliferating area of optic disk. 

CL S., cells on ventral side of yolk next to optic disks, probably representing mesoblast derived from 

wnndering cells. 
f'C.f fc.S dividing ectoblastic cells. 
Eft. J Ep.f ectoderm. 

M., ivandering cell at surface behind thoracico-abdominal fold (Fig. 108). 
Mh.f umbryonic molt. 
Md.^ rudiment of mandible. 
jWeff., mesoblast. 
O. IK, optic disk. 
0. C, optic ganglion, 
n. .*f, G., brain. 
Pd., proctodieum. 

S.^ iSJ^, products of degenerating chromatin. 
fi. C, degenerating ceUs. 
Sf. J., sternal area. 
Std.f rttomodaium. 
r„ r. S., yolk. 



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542 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 



Plate XL. 
(Stajje VI.) 

Fig* 109* Skotch of egg-Daapliu8. Auas not so clearly seen in surface view, as represented in 
thill and the following figare. Mouth on a level with antennales. x72. 

Ftu, 110. Sketeh of older embryo. Appendages all bending backwards and inwards toward 
middle line, x 72. 

Fiii. ill- Ejjg-uanplius less developed than shown in Fig. 109, but from same batch of eggs. 
Tho jKxmtion of the mouth, which is post-autennal from the first, is now on the middle 
line l>etween the antenuse and the antennules. The probable position of the anus 
is indicated, but it could not be clearly 8een. The bud which represents the endop- 
odite of the antenna is just appearing on the right side. xl57. 

Fig. 112. Oblique transverse section, through egg-naaplins of a common shore crab of Beaufort, 
North Carolina, probably Sesarma. x286. 

Fm, 113. Median longitudinal section, through a similar embryo. The egg membranes are not 
uatumJly shown. The yolk is diagramatically represented. Wandering cells occur 
]u it {Y* C), and in Pig. 113 degenerative products (Deg.) are met with. x286. 

BEFEBENGE LETTERS. 

A. {I)f AQtennal bud. 

A^ (/)f autennnlar bud. 

Jb., thoracico-abdominal fold. 

/*&;/*, degenerative cell products. 

Ep., ectoderm. 

(rtf ecto blast of neural pli^te. 

n,j mcj^blast cells, forming rudimentary heart. 

//j., birul gut. 

Lh.j hvbrum. 

Md., iriJiudibular bud. 

Men., iiif'voblast below surface. 

O. fr., optic ganglion. 

O. L,^ optic lobe. 

O. 5. iw.,S. O, G., rudimentary brain. 

Sid.^ stomodsenm. 

Tim* I vacuole. 

r. C, wandering cells. 

Numbf^fi 114-125 mark the planes of the transverse and longitudinal sections represented on Pis. 

XU'XIJLU. 



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544 MEMOIIIS OF THE NATIONAL ACADEMY OF SCIENCES. 



Platk XLI. 

(Stage VI.) 

FiGti. Hi- 118. Trau»ver»49 serial sectious of egg- uauplius in stage shown in Fig. 109. Plane of 
section indicated in Fig. Ill, which is from an embryo a trifle less advanced. The 
lobulur condition of the enlarged optic disks is well shown in Figs. 114, 115. In 
Fig. 114 a ilelaminating cell (ec.) at the surface of the optic lobe is cut, and in Fig. 
115 a sapurtkcial ectodermic cell next the brain is dividing peri>endicalarly. The 
intimatti fiiHiun of the brain and the optic ganglion is seen in Figs. 115, 116. Fig. 
1 17 cuts the .stomoiliinun passing through the mouth and the antennie. Mesoblast is 
alri'aily well (established in the pockets of all the appendages, as indicated at an 
£arM(^r iKsriod. Degenerating cell proilucts (/^., A. Y. aS., Fig. 18) are very abundant 
in the region of the stomo^lajum, and occur also in the appendages (/^.-/8.*, IS. C, Fig. 
118). xinii, 

BEFEBENCE LETTEBS. 

A. (/), autuDDal bud. 
.^. (//), aDiennnlar bud. 
J. r. S., alteration products of yolk. 

t't, tS*. c;t?lls partially covering brain, derivatives from yolk- wandering «eU8. 
ec., surface cell of ectoderm dividing horizontally. 
^d*, Kp., pctoderm. 
i/d,f luiAUilibular bud. 
Md. i*.^ mandibular ganglion. 
M. K, median furrow. 
O. ft., optic ganglion. 
" tK Zr., optiu lobe. 

Rei.y protoplasm ic reticulum. 

6'. H,\ products of cell degeneration. 

ii. O. G.5 1>rain. 

SUi.^ HtouiudsBum. 

Vav , vHtrm^le. 

y., F. a, yolk. 



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546 MEHOIBS OF THE NATIONAL ACADEMY OF SCIENCEa 



Plate XLII. 

(Stage VI.) 

F108. 119-122. Serial trauAver^e sectious of the egg-naaplias, coutioued from PI. xu. In Fig. 
120 a transverse row of cells with large clear nuclei is seen. This is probably a 
series of bndding ectoblasts and mesoblasts, already* referred ti>. Wandering cells 
appear to be settling down upon all parts of the embryo. In the thoracico-abdomi- 
nal fold (Fig. 122, mv.) the abdominal muscles are already undergoing dififerentiation 
out of the mesoblast of the ventral plate, x 295. 

BEFKBBNGE LETTEB8. 

A,t anal invagination. 
J. (//), antennal bad. 
Jb,t abdomen. 

A, Y. S.y yolk undergoing obans^. 

B. Z,f budding zone. 
Eei., ectoderm. 
Hg.y intestine. 
Md.f mandible. 

Md. O.J mandibular ganglion. 

Me8.j mesoderm. 

M. F.J median groove. 

Mu.j muscle cells. 

Mx. (i), first maxillary bud. 

«.% products of cell degeneration. 

S. C.J degenerating cells. 

r.j yolk. 

r. C, r. C.>, wandering cells. 

Vao., vacuole. 



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548 MEMOIKS OF THE ]S'AT10NAL ACADEMY OF SCIENCES. 



Plate XLIII. 
' (Stage VI.) 

FiGB, 12:^, V2L <'oTiip1t'(ioii »f series of transverse sections of egg haaplius. Cells marked Mes. 

probably ivpruseiit i*Eitloderm in Fig. 124. The heart is being formed at about this 

time out of mesobtast i^ells at //, Fig. xxiii, and the endoderm forms a plate between 

it and the eeutral yolk {v, Fig. 133). x295. 
Fm. 125. iknlian loDgitiidinat section of same stage. Compare with Fig. 106. The thoracico- 

abdomiual fold is now distinctly directed forward, an i is overgrowing the sternal 

area bi'twf^eti it and the month. The stomodsBum is a bent tube. x295. 
Fig. 126. Trau^viTse section, cutting proctodaBum. From an embryo of about the same age as 

that represented in Fi^. 106. x295. 
Fig, 127. Transverse Reetjon of einl)ryo and entire egg on level with anus, showing wandering 

cells (Y, a, Y. C,'-^). x74. 

BEF£B£NOE LKTTEB8. 

A,, anal invagination. 

Ah. J iibdomen. 

A. T. S., altered food yolk. 

CJt.j eggshell, 

^tj £p,j ecto<ierm. 

GL^ gangliuiiio ructiment. 

B'.j rudiment of heart. 

llff*f intestine. 

if ft. J embryofiio molt. 

Mfs.j inewiderm. 

M0.J iiiouth. 

Pd., rug ion of pmctodujal invagiDation. 

f^, nKj pr<Hlut;tH of cell degeneration. 

^. C.J wandering cells, probably in early stages of degeneration. 

S, (KG,^ nidi intent of brain. 

St. A.^ Ht-eroul aroa. 

Std,, Htornod^^Lim. 

F., yolk. 

K C, F. C.i -*, wandering cells. 

F, 5,, yolk opliernles. 

Fa^.j vacuole. 



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550 MEMOIE8 OP THE NATIONAL ACADEMY OF SCIENCES. 



Plate XLIV. 

(Stage VII.) , 

Fig. 12d. Transverse section throagh embryo, in the region of the first maxilla. Nervous system 
not yet differentiated from the skin, x 234. 

Fia. 129. Lateral longitudinal section through optic lobe and extremities of antennas. 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. 
X234. 

Fig. 130. Surface view of embryo of this stage, with buds of four post-mandibular appendages 
present. The antennae 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. x 137. 

Fig. 131. Median longitudinal section in the series from which Fig. 129 was taken, x 234. 

Figs. 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 
l>enod. An incomplete layer of elongated cells (probably mesoblastic in origin, com- 
ing from wandering yolk cells), Me$.j Figs. 131, 132, is seen between the yolk and 
the neural thickening, from which the nervous system is in process of development. 
In Fig. 134 rudimentary muscles suspend the stomodaeum 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. x234. 

BEFEBENCE LETTEBS. 

A. /, first antenna. 

A. II, Becoud antenna. 

Ah.y thoracico-abdominal fold. 

A. F.S,, alteration productH of the yolk. 

Ect.f ectoderm. 

End.f endoderm. 

G. L., rudiment of optic ganglion. 

01. J, II f antennnlar ganglion. 

Lb.f labrum. 

Mea,, mesoderm. 

Mo., mouth. 

Mu.f rudimentary mnscles. 

Mx. I, first maxillary bud. 

O. E., retinal portion of optic lobe. 

S. O. G,, brain. 

8id., 8tomod»um. 



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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Platk XLV. 

(Stage VIII.) 
• 

Fig. 136. Lateral loagitudlual section of embryo In Rtage intermediate between YII and YIII, 
represented in sarface view in Fig. 110. To this phase also belong Figs. 13*7, 144, 
and 145. Fig. 136 is to be compared with the slightly older embryo in Fig. 129. 
Blood cells (B. C) and other wandering cells are here seen settling down npon the 
body wall. A wandering cell is also seen nearly in contact with the optic ganglion. x241. 

Fig. 137. Transverse section of embryo in same phase, just behind the level of the first antennas, 
showing the relations of the wandering cells at this period to the embryo and egg, x 61. 

Figs. 138, 139. Serial longitudinal sections through embryo in Stage VIII. Fig. 138 should be 
compared with Figs. 136 and 120. 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 ganglia of 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. 
X24L 

Figs. 146-143. Parts of sections taken at various points on the surface of the egg (series to which 
Figs. 136, 137, 144, 145, belong), remote firom the embryo, to show the r6le of certain 
wandering cells which reach the surface and represent mesoblast. In Fig. 140 two 
cells (mB.y fM.^) are partially flattened against the surface, but here, as in Fig. 142, 
the wandering cell ms. is clearly distinguishable from the spindle-shaped ectoderm 
cell on the left. Compare Fig. 34. x241. 

Figs 144-445. 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 (!>}>•) — 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. 

BEPEBENGE LETTERS. 



A. If first antenna. 

A, H, second antenna. 

an. J lower margin of optic lobe. 
A.B.a.t superior abdominal artery. 

B. C.f blood corpuscle. 

b. m., basement membrane. 

oh,y eggshell. 

Dp., dorsal plate. 

End,t endoderm. 

G. IV'XVIIIf segmental ganglia. 

Gl.f gangliogen. 

H., heart. 

hd., hypodermis. 

Hg,, hindgat. 

mes.f mesoblast. 

mo., mootb. 

fM., ms.^, wandering cells at surface. 

O. L., optic lobe. 

RU, retinogen. 

Sid., stomodsBum. 

Th. ah., thoracic-abdominal fold. 

y,o,, wandering cells. 



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554 MKMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XLVI. 

(Stage IX.) 

Pros. 146-151. Serial transverse* sections, through the embryo oi A. iaulq^j at the time when 
pigment is first deposited in the eye. In Fig. 140 the developmental history of the 
retinal layer is well shown, x 230. 

Fto. 151^, Nearly ui^iiian longitudinal section of embryo in similar stage. x58. 

Fig. 15^. Sagittal tieution of similar embryo, showing degenerating elements in yolk below dorsal 
platfi< x58. 

BBFEBENCE LETTES8. 

J. /, first anteuna. 

A. II, second antenna. 
Ab,, abdomen. 

B. C.f blood corposole. 
B. 8,^ blood space. 
cp.f carapace. 

Deg., degenerating cells. 
Dp.f dorsal plate. 
End,f endoderm. 
ftj.f foregat. 

f$., fiber mass of nervous system. 
g.II-III, brain. 
^ 9' ^'f ganglion cell. 

g. m. a. , anterior gastric muscle. 
H.y heart. , 

hd.y hypodermis. 
Hg.f hindgut. 
X6., labrum. 
Md,f mandible. 
Mes.f mesobiast. 
A/tf./., flexor muscle. 
Qcm., oesophageal commissure. 
o,g., optic ganglion. 
O. X., optic lobe. 
pk., punct Bubstanz. 
pr., perineurium. 
Et,f retinogen. 

8, 0, O., supra-oesophageal ganglion. 
T., telson. 
T Tcy transyerse commissure. 

Th., thorax. 
Vao,, vacuole, 
y., yolk, 
r. C, wandering cells. 



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556 MEMOIRS OF THE NATIONAL ACADEMY OF 2SCIENCE8. 



Plate XLVII. 

(Stage IX.) 

Fi(^. I54f 155. Transverse sectionB throagh eotire enibr>o of A1pheu$ «ai(loyi. In Fig. 154 a yolk 
nest is cat. Blood spaces occur near the surface of the egg. x61. 

Fig. 156. Cell uest, containing degeneration prodaots. Its position in the yolk is shown in Fig. 
154. x245. 

Fig. 157. Part of median longitudinal section throagh the thoracic-abdominal flexure. The grow- 
ing endodermal epithelium and its fusion with the lining of the intestine are particu- 
larly well shown. Wandering cells appear to be uniting with the endoderm. x245. 

Fig. 158. Sketch of egg embryo, Alpheus saulcffiy of same phase as that represented by Fig. 157. 
x61. 

Fig. 159. Horizontal section through brain and eyestalksof a slightly older embryo. xOl. 

Fig. 160. Part of transverse section o? simitar embryo on level with the mandibles. x245. 

Fig. 161. Superficial part of section of egg, showing surface cells, blood corpuscles, and a wander- 
ing cell on the edge of the blood ^pace. x245. 

KEFERENOR LETTERS. 

A, J, tirst auteuna. 

A, J If aecoud antenoa. 
Ab,f abdomen. 

aor,, aorta. 

a. y. 8., granalated yolk prodnoto. 

B, C, blood cell. . 
B. S,y bk>od space. 
Ck., eggBhell. 

c/;.y carapace. 

Oeg,f products of cell degeueration. 
Ed, J ectoderm. 
End,, endoderm. 

fa.f fiber-Bubetance of nerve cord. 
O, IF, ganglion of mandible. 
gc, ganglion cell. 
gf., fiber ball of second antenna. 
H., heart. 
hd,, bypodermis. 
hg,f bindgnt. 

If,, lateral fiber-mass of brain. 
Md,, mandible. 
Me8,f mesoblast. 
Mu.f mnscle cells. 
Mu,f,f flexor mnscle. 
SiU,, metastoma. 
n. c,f nenral cord. 
O. 0,f optic ganglia. 
of.f optic enlargement. 
p. C.J pillars of carapace. 

p, r.y perineurinm. / 

p, «., pericardial sinns. 
Ri,, retinogen. 
Sid,, stomodienm. 
vac, yacnole. 
y, c, wandering cell. 
y, n,y yolk nest. 



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558 MEMOIBS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XLVIII. 

(Stage X.) 

Fios. 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. x57. 

Figs. 166 — 167. Parts of serial ti[*ansverse sections of the embryo of Athens saulcyu x 125. 

Fig. 168. Median longitudinal section through a slightly older embryo, showing the ventral 
endodermic fold (/), the foregnt still screened from the yolk, and the nervous 
system separated from the skin. x227. 

EEPEBBNCE LETTERS. 

Ab y abdomen. 

Ab, g. I, first abdominal ganglioD. 

aar.y aorta. 

B. C\, blood cell. 

B,S., blood space. 

ec, crystalline cone cells. 

Deg,f products of degeneration. 

Eep.f proximal retinular cells. 

End,, endoderm. 

/., ventral endodermic fold. 

g. m, a.f anterior gastric mnscle. 

H., heart. 

Hg,j hindgat. 

imb,y intercepting membrane. 

mg., mesenteron. 

mo,, month. 

mpgl, first maxillipedal ganglion. 

ifai. E,, extensor muscles. 

Mu.f.y flexor muscles. 

O. G.y optic ganglia. 

p, 8,, pericardial sinus. 

RU, retinogen. 

S, O, G; snpra-ODSophageal ganglion. 

T., telson. 

Tk., thorax. 

Th, g. I, ganglion of first ambulatory limb. 

y. c, wandering cells. 



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560 MEMOIBS OF THE NATIOi^AL ACADEMY OF SCIENCES. 



Plate XLIX. 
(Stages X and XII.) 

Figs. 169-173. Parts of serial transverse sections through the embryo of Alpheus saulcyi in Stage 
X. In Fig. 173 the reproductive organ R. 0. is cut xl29, (Fig. 173, x234.) 

Fig. 174. Horizontal section through nervous system of the first larva, on a level with the (Esopha- 
geal commissures, x 234. 

Figs. 175, 176. Transverse sections through the neural cord of the first larva. In Fig. 176 the 
transverse commissure of the ganglia of the tenth segment is cut and m Fig. 175 
the short longitudinal commissui-es between the tenth and eleventh segments are 
sectioned, x 129. 

BEFEBBNCE LETTERS. 

A. If first antenita. 

A, II, second aDtenna. 
Ab,, abdomen. 

ag,f antennal glaud. 
B» c, blood corpascles. 

B, S,t blood siDQs. 
Br,, brancbia. 
op., carapace. . 
End, J endoderm. 
fg.f foregut. 

g. 0., ganglion cell. 

Hd., hypodermis. 

Hg,, hindgut. 

l.f,f lateral fiber- mas8 of brain. 

Md,, base of mandible. 

Mes.f mesoderm. 

Mg.f mesenteron. 

Mu.y mascle. 

Mu. e.f extensor muscles of abdomen. 

Mn.f.f flexor muscles of abdomen. 

Mx., base of maxillce. 

Mxpd,, baseof maxillipedH. 

n.c, neural cord. 

o/.y optic fiber-mass of bram. 

o.g., optic ganglion. 

Pr., perineurium. 

B. O.J reproductive organ. 

Hog.j brain. 

U c.y transverse commissure. 

y. c, wandering cells. 



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562 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate L. 

(Stage XI.) 

Figs, 177-170, 181, 182. Serial transverse sei'tions of the embryo of Alpheus heterocheliSf which is 
irt'drly ready to hatch. The shell is soiuewhat diagraiuaticaily represented audapi>ears 
thickened in Fig. 182, owing to a coagulable substance beneath it The c^lls rep- 
resented in the yolk in Fig. 182 appear to be endoderm cells, which have become 
mechanically detached from the walls of the meseuteron. x74. 

Flo. 180. Nearly median longitudinal section through a similar embryo. The eudodermal lining 
of the mesentcron is not yet nearly completed, x 74. 

REFERENCE LETTERS. 

Jb,f Vly gauglion of sixth abdomiual appendage. 

ag.f antennal gaugliun. 

ai«.y anus. 

ch, ex., external chiasnia. 

ecUf ectoderm. 

end., endoderm. 

fg,, foregut. 

gua.y anterior gastric muscle. 

J7., heart. 

hg.^ hindgut. 

hy.^ hypodermis. 

y., lateral fiber-mass of brain. 

mg.f mesenteron. 

mg.^ mg.^ of other figures, poslcrioi- h)be of midgut. 

mii.f.f fiexor muscles (»f midgut. 

mu, e., extensor muscles of midgut. 

ocm.y oesophageal commissure. 

o,pd,^ optic peduncle. 

Ret.^ retina. 

8og,^ brain. 

r., telson. ' 

1-4, ganglia of e.ve-stalk. 



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564 MBMOIK8 OP THE NATIONAL ACADEMY OF SCIENCES. 



^ T^.ATE LT. 

(Stage XL) 

Figs. 18:^-186. Continuation of aeries of transverRe sectionR of embryo begun on Plate L. x74. 

Fig, 187, Part of sagittal section of similar embryo, cutting eyestalk somewhat obliquely. The 
specimen was depigmented in nitric acid. The distal retinular cells, occupying the 
spaces {Fg. c.) between the peripheral ends of the cones, are not represented. x305. 

REFERENCE LETTERS. 

oc*. I'.j accessory pigment cells. 

ad, m.f adductor of mlindible. 

a. sa.f saperior abdominal artery. 

hg,y braYicbiosteglte. 

h. r., blood vessel. 

c. . crystaUine cone. 

eg. J corneagen. 

ect.f ectoderm. 

end.y endoderm. 

fg.y foregnt. 

//., heart. 

Ay., bypodennis. 

imb.f intercepting raembranp. 

mg.y midgut. 

mg.^y posterior lobe of midgut. 

Mu.j muscle of eyestalk. 

Mh. e.j extensor mnscles of abdomen. 

Mu.f.y flexor mnscles of abdomen. 

o. c. m.y wsophageal commissure. 

Pg. C.y position of distal retinular cells. 

P«., pericardial sinns. 

Riu., proximal retinular cells. « 

RtuJ, nuclei of proximal retinular cells. 

3, 4, ganglia of eyestalk. 



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566 MEMOIRS OF THE NATli>NAL ACADEMY OF SOIBNOB& 



1>T.ATE LIT. 

Figs. 188, 189. Parts of traDSverfle aerial sections through the embryo of Pakemonetes vulgaris^ at 
the stage when pigment is jast appearing in the eyes. In the anterior section (Fig. 
188) the retinogen is a anicellular layer. x305. 

Fios. 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 of 
cells which represent the ommatidia are well shown. Numerous ganglion cells are 
dividing. x305. 

Fig. 192. Part of transverse section through eye, optic ganglion, and brain at a later stage, x 305. 

BKPEBENOR LRTTRBS. 

A.Tj first antenna. 

Ab., abdomen. 

cc,f crystalline cone ceUs. 

imh.f intercepting membrane. 

mes.j mesoderm. 

Ret., retina. 

rtV, rudimentary eighth proximal retinnlar eelL 

8og.j brain. 

T., telson. 

X,f stratnm of large ganglion cells. 

1, lif 4j proximal, external middle, and distal segments of optic ganglion. 



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MEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 



PhATK LIIL 

Fig. 193. Part of transverse sectiou through au embryo of Alpheua aa^Ucyi^ which is uearly ready 
to hatch, showing the third left branchia covered by the branchiostegite. x 289. 

Fig. 194. Part of sagittal section of eyestalk of a slightly younger embryo. x289. 

Fig. 196. Part of transverse section, showing branchia, of the thiril larva of Alpheun naulcyi (twenty- 
four hours old). x289. 

Fig. 196. Nearly median longitndinal section of first larva of same. The anterior lobes of the 
midgut (mg^) still contain unabsorbed yolk. Compare PL xxi, Fig. 1. x58. 

Fig. 197. Part of transverse section, showing the papilla, which bears the median eye in the first 
larva of same, x 289. 

Fig. 198. Transverse section of first larva, cutting the lateral fiber balls of the brain, the anterior 
lobes of the"" midgut, and the green gland. x289. 

Fig. 199. Part of transverse section through an advanced embryo of A/p/teii« ^ait^cyi, parasitized 
by a fungus, most of the cells of which are encysted!. From brown sponge, Abaco, 
Bahama Islands, v. Appendix II. x 186. 



EEPEBENCE LETTERS. 



db.y abdomen. 

Ah, VI f sixth abdomiual apptrnda^e. 

acp.f accessory pigment cells. 

ag.f green gland. 

ag.a.f end sac (f) of gland. 

as. a.f superior abdominal }u>rta. 

bg.y branchiostegite. 

h. 8,f B. S.f blood space. 

hr.^f branchia of third left anibiilat4)ry limb. 

cc, crystalline cone cells. 

cg.f comdagen. 

«?., lens. 

CO., crystalline cone. 

C8.f c».'-*, cysts of parasite. 

cs.\ smaller, naked cells of parasite. 

g.* 20^ segmental ganglia. 

gf.f tiber-mass of second antennu'. 

gma.f anterior gastric muscle. 

M.f heart. 

Hd.f hypodermis. 

Ifg.f hindgut. 

Lb., labrum. 

L c, longitudinal commissure. 

m//., midgut. 



fngJ, anterior lobes of midgut. 

mg.'^, lateral lobes of midgut. 

mg.^, posterior lobes of midgut. 

mo., month. 

mt,, masticatory stomach, 

mu. e., extensor muscles of alxlomen. 

mu.f.f flexor muscles of alMlomen. 

H, c, neural cord. 

oc., ocellus. 

oe., oesophagus. 

O.G.f o.g.f optic ganglion. 

of,, optic enlargement of brain. 

op., ophthalmic artery. 

pt,, pericardial sinus. 

pr., perineurium. 

R., rostrum. 

Ret., retina. 

rtl,, nucleus of proximal retinnlar cell. 

8og., brain. 

Sp., parasitic growth. 

St. 8., sternal blood sinus. 

r.. telson. 

y.y yolk. 



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570 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES, 



Plate LIV. 

Fig. 200. Ommatidiam of ejeof small adult Alpkem muUryi (fVom brown sponge) ; pigment removed 

* by nitric acid. x294. 
Figs. 201-204. Transverse sections through four adjacent omuiatidia of first larva of same. In Fig. 

201 the comeagen is cut, and in Fig. 202 the nuclei of the cone moth^ cells. In Fig. 

204 the rhabdoni is sectioned and the seven proximal retinnlar cells. x294. 
FiGR. 205-208. Transverse sections through atljacent 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 retinnlar cells api)ear in sections, as if fuHe<l together, x 294. 
Fios. 200-211. Transverse serial sections through the first larva of Alpheus saulcyi. x 74. 

REFERENCE LETTERS. 

A, If first anteuna. 

A, II, second antenna. 

a. op.t accessory pigment cell. 

acpn.'f nocleus of accessory pigment cell. 

ao.y ear. 

Bm,, intercepting or basement membrane. 

00. y crystalline cone cells. 

0^., corneagen. 

cl,f lens. 

Co,f CO., crystalline cone. 

omh,, cone membrane. 

hd., bypodermis. 

me.f membrane of distal retinnlar cells. 

^f., nerve fibers. 

00., ocellns. 

og,, optic ganglion. 

of,, optic enlargement of brain. 

pop., papilla of ocellns. 

p, g. c.f distal retinnlar cells. 

R,, ruetrnm. 

Rh.f rb., rbabdom. 

Bet,, retina. 

rtl., proximal retinnlar ceUs. 



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572 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate LV. 

(Stage XII.) 

Ftgs. 212-223. TrauHverHe serial sections of the first larva of Alpheua Mauleyi from the same indi- 
vidual as Figs. 209-211, excepting Figs. 222, 223. x 73. 4 

REFERENCE LETTERS. 

I 

A. Iff second aotenna. 
ad. m,, addactor of mandible, 
oj/., greeu gland. 

a/., antenniilar fiber- masn of brain. 
ao,f ear. 

a. op. J ophtbalmic artery. 
Bg., branch iofltegite. 
B.gl.f gland-like body. 
B.S.f blood sinna. 
/</., foregut. 

fo.t fiber-mass continued into cesophageal commissnre. 
gf.f antennal fiber-mass. 
gf.f lateral pouch of masticatory stomach. 
Lb.f labrum. 

//., lateral fiber-mass of brain. 
Md.f mandible. 
Mg.f midgut. 

MgKf anterior lobe of midgut. 
Mg^., lateral lobe of midgut. 
Mj>., septnm between anterior lobes of midgnt. 
M. S.y masticatory stomach. 
Mts., metastoma. 
Mx. /, first maxilla. 
"—- ^ — Mxpd. /, first maxilliped. 

n. ag.^ antennal nerve. 
II. o«., antennular nerve, 
oc, ocm.f iBsophageal commissnre. 

of., anterior fiber-mass and transverse commissnre of brain. 
p. v., pyloric valve of masticatory stomach. 
Bi. «., sternal sinus. 



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574 MEMOXKS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate LVI. 

(Stage XII.) 

Figs. 224-235. Serial transverse sections throagh the first larva^ continued from Plate LV. x73. 

BEF&BENOB LKTl^EBS. 

Ah, V, fifth abdominal appendage. 

a. f. a,j iDferior abdominal aorta. 

a. op,, ophthalmic artery. 

a. 9. a., superior abdominal artery. 

bg.f branchioHtegite. 

6r., branohia of ambulatory appendage. 

B, 8., blood sinus. 

gg, ^-^y middle, ventral, and dorsal lobules of posterior lobe of midgut. 

H., heart. 

hg.y hindgut. 

hy.y hypodermis. 

Ic, ih.~ab., longitudinal commissures uniting last thoracic with first abdominal ganglia. 

Mg.f midgut. 

Mg, ^, lateral lobe of midgut. 

Mg, ^ posterior lobe of midgut. 

Ms., masticatory stomach. 

Mu. e.y exteusor muscles of abdomen. 

Mu.f., fiexor muscles of abdomen. 

Mxpd. I-III, fimt to third maxillipeds. 

pleu., pleuroD. 

ps.y pericardial siuus. 

Th, /-F, first to fifth ambulatory limb. 



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570 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate LVII. 

(StajjeXU.) 

Figs. 236-245. Horizontal sectionn of first larva, illustrating further the anatomy of the alimen- 
tary tract and the nervous system. xo7. 

HKFKREN( £ LETTKRIS. 

J. /, 77, tir»t and »ecoiid anteima. 

o^.. greon fi^laud. 

a/., antennnlar Aber-itiasH. 

ao.f ear. 

bg., branchiostegite. 

End.f eDdoderm. 

fg,y foregnt. 

fo.t flber-tabstanoe of aHK>ph»geal commlMtire. 

gf,f ftber-maM of teoond antannie. 

gg, 1-^, middle, ventral, and dorsal diviaioni of posterior lobe of midgnt. 

kg,, hindgat. 

//., lateral fiber mass of brain. 

Md.j mandible. 

Mg.y midgnt. 

yfg.^f lateral lobe of midgut. 

Mp.f partition betweeu anterior lobeH of midgut. 

^f^tf,^ metastoma. 

Mx, If II, first and second maxilUe. 

Mxpd. I-III, first to third roaxillipeds. 

n. an.f antennnlar nerve. 

n.c.f ventral nerve-cord. 

of.y anterior fiber-mass of brain. 

o^., optic ganglion. » 

Ret. J retina. 

l^h. /-F, first to fifth ambulatory limbs. 

y., yolk. 



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