CHAPTER XII_The Life of Crustacea

CRUSTACEA OF THE PAST

Since the acceptance by naturalists of the theory of Evolution as

indicating the mode of origin of the various forms of life now existing,

one of the chief lines of biological investigation has had for its

object the reconstruction of the pedigree (or, as it is called, the

"phylogeny") of the larger groups of the animal and vegetable kingdoms.

In attempting to do this, there are three main sources from which

evidence may be drawn. The results of Comparative Anatomy enable us to

decide with more or less confidence as to the degrees of relationship

between the groups of organisms, and to distinguish between the more

primitive and the more specialized; the study of Embryology is, at

least, an indispensable adjunct to Comparative Anatomy, even if it does

not, as was once supposed, give us an actual recapitulation of ancestral

history; and, finally, the study of Fossil Remains holds out the hope

that we may be able to find the ancestral types themselves.

It is clear that evidence from the last-named source, when it is

available, is the most important of all, since the order of succession

of the various types is given by that of the rock strata in which they

occur, and we can be quite certain that we are dealing, if not with the

actual ancestors, at least with the forerunners of existing species. The

"imperfection of the geological record," however, is so great that the

organisms preserved in the fossil state represent only an insignificant

part of the whole number of organisms that have lived on the globe since

life began; and it is not surprising, therefore, that in many groups the

study of fossils has hitherto afforded little help towards the working

out of their genealogical history. Thus, among Crustacea there are many

important groups such as the Copepoda, which are entirely unknown as

fossils, their small and delicate bodies being ill adapted for

preservation, although there is every reason to suppose that they are a

very primitive and very ancient group. In many fossil Crustacea only the

hard shell or carapace has been preserved, the appendages being lost or

represented only by indecipherable fragments, and in some cases it is

hardly possible to guess at the affinities of the animals. Further,

several important groups are already represented in some of the oldest

of the fossil-bearing rocks at present known, and the differentiation of

these groups must have taken place in the dark ages before the record of

the fossils begins. In spite of these disadvantages, however, the study

of fossil Crustacea does throw considerable light on the evolution of

the group, and it is likely that interesting results in this direction

await future investigations.

[Illustration: FIG. 81--RESTORATION OF A TRILOBITE (_Triarthrus becki_),

SHOWING THE APPENDAGES. UPPER SIDE ON RIGHT, UNDER-SIDE ON LEFT.

SLIGHTLY ENLARGED. (After Beecher.)]

In the earliest fossiliferous rocks the most abundant and important

Arthropods are the Trilobites (Fig. 81), an extinct group which appears

to have been related to the primitive Crustacea. The name Trilobite

refers to the three-lobed form of the body when seen from the dorsal

side, most species having a pair of grooves running lengthwise which

divide off a middle lobe containing the principal organs of the body

from two lateral "pleural" expansions covering the limbs. The

head-shield shows indications of being composed of five segments, and

bears a pair of sessile compound eyes. It is followed by a number (up to

twenty-six) of free somites, and the body ends in a tail-shield, or

"pygidium," which is often plainly composed of several somites fused

together. Although Trilobites are among the commonest and most familiar

of fossils in the older rocks, the nature of their appendages remained

quite unknown until within recent years, when specimens of several

species showing the structure of the limbs and under-side of the body

were discovered in America. From these it appears that the head bore in

front a pair of long thread-like antennae and four pairs of two-branched

appendages, each with a jaw process, or "gnathobase," turned towards the

mouth, which is covered below by a large anterior lip, or "hypostome."

It seems probable that the five pairs of head-appendages correspond

respectively to the antennules, antennae, mandibles, maxillulae, and

maxillae, of Crustacea; but the second pair appear to have acted as jaws,

retaining the gnathobase which, among Crustacea, is only hinted at by

the hooked spine on the antenna of the nauplius larva.

Each of the free somites and of those forming the tail-shield bears a

pair of two-branched appendages, not differing greatly from the

posterior appendages of the head, but becoming smaller and more

flattened towards the hinder end of the body. The numerous genera and

species of Trilobites present great differences in the form and

ornamentation of the dorsal surface of the body, and it is probable that

considerable differences may also have existed in the structure of the

limbs, which are only known in two or three species. Some Trilobites are

among the most ancient of known fossils, being found in rocks of the

Lower Cambrian epoch. The group reaches its maximum development in the

Ordovician, and the number of the species and size of the individuals

gradually diminish through the Silurian and Devonian till they become

extinct at the close of the Carboniferous epoch, except for a single

species found in rocks of Permian age in America.

Although zoologists are not all agreed as to the precise systematic

place to be assigned to the Trilobites, there can be little doubt that

they were related more or less closely to the most primitive Crustacea,

and they are of special interest as preserving for us the stage in which

the second pair of appendages were still used as biting jaws, and had

not moved forwards in front of the mouth to become antennae, as in all

living Crustacea.

Contemporary with some of the earliest Trilobites, however, are

undoubted Crustacea, which, so far as we know their structure, are not

very different from types now living. In the Cambrian epoch the

Branchiopoda appear to be represented by _Protocaris_, which in its

general form resembles _Apus_; and there are a variety of genera and

species of Ostracoda, although, since their shells alone are preserved,

it is not possible to determine their exact relations to existing forms.

In the succeeding Ordovician and Silurian epochs we first meet with the

remains of Barnacles, and it is interesting to note that some of them

are referred to the genera _Pollicipes_ and _Scalpellum_, which are

represented by numerous species in the seas of the present day. Along

with these, however, are some strange-looking forms (_Turrilepas_,

etc.), having the body covered with rows of overlapping plates. If these

are really Cirripedes, they must have differed considerably in structure

from the more modern types.

The Malacostraca are more interesting from the point of view of

palaeontology than the other subclasses of Crustacea, since the evolution

of the group appears to have taken place within the period covered by

the fossil records, and it is possible to trace the course of that

evolution--at least, in its broad outlines. It has already been pointed

out that the most primitive of existing Malacostraca are the

Phyllocarida (_Nebalia_ and its allies), which are in several respects

intermediate between the higher Malacostraca and the Branchiopoda; and

it is interesting to find that fossils apparently belonging to the

Phyllocarida are found far earlier than any of the other Malacostraca.

In the Cambrian, and more abundantly in the Ordovician and Silurian,

there are found Crustacea (Fig. 82) that resemble _Nebalia_ in having a

large bivalved carapace, with a movable beak-like plate in front, a

projecting abdomen without conspicuous limbs, and a pair of large spines

at the sides of the telson. Unfortunately, we have almost no knowledge

of the structure of the limbs; but it can hardly be doubted that these

very ancient Crustacea were allied to the existing Phyllocarida, and

that they included the forerunners of the higher Malacostraca.

[Illustration: FIG. 82--_Ceratiocaris papilio_, ONE OF THE FOSSIL

PHYLLOCARIDA. (From Lankester's "Treatise on Zoology," after H.

Woodward.)

_a_, Traces of antennules; _m_, possibly mandibles; _r_, rostral plate]

It is in the Carboniferous epoch, in all probability, that we must look

for the origin of most of the existing orders of Malacostraca. In the

rocks of this age in different parts of the world there have been found

a number of undoubted Malacostraca, nearly all of the shrimp-like form

which there is good reason to believe to be a primitive characteristic.

Some of these (_Pygocephalus_--Fig. 83) have recently been shown to

possess a brood-pouch formed of overlapping plates on the under-side of

the thorax, and thus resemble the existing Mysidacea, which stand at the

base of the Peracaridan series of orders. Others have a pair of strong

side-spines near the tip of the telson, and in other ways resemble the

recent Euphausiacea, so that they may have been primitive members of the

Eucaridan series.

[Illustration: FIG. 83--_Pygocephalus cooperi_, FROM THE COAL-MEASURES:

UNDER-SIDE OF A FEMALE SPECIMEN, SHOWING THE OVERLAPPING PLATES OF THE

BROOD-POUCH. (From Lankester's "Treatise on Zoology," after H.

Woodward.)]

[Illustration: FIG. 84--THE TASMANIAN "MOUNTAIN SHRIMP" (_Anaspides

tasmaniae_), A LIVING REPRESENTATIVE OF THE SYNCARIDA. SLIGHTLY ENLARGED

_c.gr._, "Cervical groove," marking off the first thoracic somite;

ii-viii, the remaining thoracic somites; 1-6, the abdominal somites]

Among the Crustacea of the Carboniferous and Permian epochs, there are a

number of forms of which the affinities were until recently quite

obscure. They have two-branched antennules, a scale-like exopodite on

the antenna, and the last pair of appendages (uropods) form, with the

telson, a tail-fan. In these points they resemble the shrimp-like

forms, but there is no carapace, and all the somites of the thorax are

distinct, so that the form of the body is rather that of an Amphipod or

Isopod. On the discovery of the remarkable Crustacean _Anaspides_ (Fig.

84), which lives in fresh-water pools in the mountains of Tasmania, it

was pointed out that it agreed with the fossil genera _Uronectes_,

_Palaeocaris_, and their allies, in those very characters in which they

differed from all other Crustacea, and that it must be regarded as a

surviving representative of the ancient group to which the name of

Syncarida had been given. The more recent discoveries of living forms,

_Paranaspides_ from the Great Lake of Tasmania and _Koonunga_ from

fresh-water pools near Melbourne, and of the fossil _Praeanaspides_

(Fig. 85) from the Coal-measures of Derbyshire, have tended to support

this conclusion. There can be little doubt that the Syncarida arose

during the Carboniferous epoch (or earlier) from primitive shrimp-like

forms which lost the carapace; but, after flourishing for a relatively

brief period, the group dwindled away, although a few survivors have

lingered on, like so many other "living fossils," in the isolated

Australian region.

[Illustration: FIG. 85--_Praeanaspides praecursor_, ONE OF THE FOSSIL

SYNCARIDA, FROM THE COAL-MEASURES OF DERBYSHIRE. SLIGHTLY ENLARGED.

(After H. Woodward.)]

It must be pointed out that, in spite of the resemblance of the body of

_Anaspides_ to that of an Amphipod, the Syncarida can have had no close

relation to the origin of the Isopoda and Amphipoda. These have also

been derived from a shrimp-like type, but their possession of a

brood-pouch, among other characters, shows that they are linked on to

the Mysidacea, and must have arisen from some primitive member of that

group, like _Pygocephalus_. Although palaeontology as yet gives little

help in tracing the course of their evolution, we can imagine what the

intermediate links must have been like by comparison with the living

Cumacea and Tanaidacea.

It is possible, indeed, that the divergence of the Isopod line of

descent from that of the Mysidacea took place earlier than the

Carboniferous epoch, for there has recently been discovered in rocks of

Devonian age in Ireland a single specimen of a fossil, to which the name

of _Oxyuropoda_ has been given, which has every appearance of being an

Isopod. At all events, undoubted Isopods make their appearance in rocks

of the Secondary Period, and some of those from the Jurassic epoch are

not very different in general form from types still existing.

Some of the Carboniferous shrimp-like Crustacea present characters which

seem to point in the direction of the Stomatopoda, and fossils which

clearly belong to that group are found in Jurassic and later deposits.

In the Cretaceous epoch there were Stomatopoda resembling modern types

so closely that they have been referred to the existing genus _Squilla_.

We are even able to say that they resembled the living Stomatopoda in

their mode of development, for larvae of the type known as _Erichthus_

have been recognized in rocks of Cretaceous age from Lebanon. This is a

striking example of the way in which, by a fortunate accident as it

were, organisms apparently ill-adapted for fossilization may

occasionally be preserved.

Of the Decapoda the geological history is tolerably full, and it is

possible to trace in its broad outlines the course of evolution of the

various suborders. Here again it is likely that the beginnings of the

group are to be sought for in the Carboniferous epoch, and some of the

obscure shrimp-like forms of that age show hints of an affinity with the

Decapods. In the Triassic epoch, however, and more abundantly in the

succeeding Jurassic, a number of types are found which seem to include

primitive representatives of several of the existing groups of Natantia

and Reptantia. It is noteworthy that among them are some forms (_AEger_,

etc.) resembling the existing Stenopidea, a tribe which in some respects

is intermediate between these two suborders. In the Stenopidea the first

three pairs of legs bear pincer-claws, as in the Lobster, but the third

pair is much the largest; and _AEger_ agrees with them in this unusual

character, though there is little else, in what is known of its

structure, to help to determine its affinities.

The tribe Penaeidea, which occupies in many respects a primitive place

among the Natantia, is abundantly represented in the Jurassic epoch,

especially in the lithographic stone (Upper Jurassic) of Solenhofen, and

by somewhat doubtful specimens from the earlier Trias. All these agree

in having the first three pairs of legs with pincer-claws, and not

differing greatly in size. Some of the Jurassic and later fossils are of

so modern a type that they have been referred to the existing genus

_Penaeus_.

The Upper Jurassic rocks also preserve the earliest undoubted specimens

of true Prawns of the tribe Caridea, and some of these show swimming

branches (exopodites) on the thoracic legs, so that they were probably

related to the primitive family Acanthephyridae, of which the existing

members are found in the deep sea. It is possible, however, that Caridea

were already in existence far earlier, for some of the obscure

Carboniferous forms seem to have the broadened side-plates of the second

abdominal somite, which, so far as we know, are exclusively

characteristic of that tribe.

The Reptantia, forming the other large division of the Decapoda, also

had their origin at least as early as the Triassic epoch, where

representatives of the tribes Eryonidea and Scyllaridea are found. The

history of the Eryonidea has already been discussed (p. 133) in dealing

with the deep-sea Crustacea. The oldest representatives of the

Scyllaridea belong to a family (Glyphaeidae) now wholly extinct, and are

in many respects more primitive and lobster-like than any of the living

Spiny Lobsters and their allies (Palinuridae and Scyllaridae). Forms with

greatly thickened antennae, indicating a transition to the Palinuridae,

begin to appear in the Jurassic; and in the later Cretaceous a genus,

_Podocrates_, occurs which is hardly to be distinguished from

_Linuparus_, now living in Japanese seas. The Scyllaridae have the

antennae modified into broad shovel-like plates, and perhaps take their

origin from _Cancrinus_, in the Solenhofen lithographic stone

(Jurassic), which has broad and apparently flattened antennae. True

Scyllaridae are certainly found in Cretaceous deposits, and some, from

the Upper Chalk, are even referred to the existing genus _Scyllarus_.

The Anomura are almost unknown as fossils, but the true Crabs, or

Brachyura, are abundantly represented. They first appear about the

middle of the Jurassic epoch, and, as already pointed out, the earliest

forms (Prosoponidae) are referred to the Dromiacea, and appear to be

closely related to the primitive Homolodromiidae now living in the deep

sea (p. 134). One of the oldest, and at the same time one of the most

completely known, is _Protocarcinus_, from the Great Oolite of

Wiltshire, which is preserved (in the only known specimen) with the

abdomen partly extended, possibly indicating that the abdomen was less

closely doubled under the body than in modern Crabs.

The next group of Crabs to appear are the Oxystomata, which are found

from the middle of the Cretaceous epoch onwards. The Brachyrhyncha

perhaps begin to appear about the same time, but the affinities of the

earlier types are doubtful, and it is only in the Tertiary that they

become abundant and unmistakable. Several living genera, such as

_Cancer_, date back to the Eocene. The Spider Crabs (Oxyrhyncha) are

rare as fossils, and the earliest specimens are found near the beginning

of the Tertiary.

APPENDIX

I. METHODS OF COLLECTING AND PRESERVING CRUSTACEA

It may be useful to give here a few hints as to the methods of

collecting Crustacea. Of the species that live in the sea, many may be

found between tide-marks by turning over stones and searching among

sea-weeds and in rock crevices. A small hand-net, made by fastening a

bag of coarse muslin to a stout wire ring of a few inches diameter, is

useful for fishing in rock pools. Shore-collecting in this manner is

most productive at spring-tides, when the deeper levels of the shore are

open to exploration.

Many burrowing species are to be found by digging in the sand near

low-water mark. In addition to Crabs and other large species, many

minute forms, Amphipods, Cumacea, and the like, inhabit such localities.

The best way of collecting these is to stir up a spadeful of the sand in

a bucket of water, and, after allowing the sand to settle for a few

seconds, to pour off the water through a muslin bag. After repeating the

operation two or three times, the contents of the bag are washed out

into a jar or dish of sea-water for examination with a lens or under

the microscope.

Dredging is the most effective method of obtaining Crustacea that live

in deeper water. The dredge usually employed by naturalists consists of

a heavy rectangular iron frame to which is attached a strong bag-shaped

net. The two longer sides of the frame are sharp-edged and bevelled

outwards, so as to "bite" when the dredge is dragged along the

sea-bottom. To the shorter sides are hinged a pair of arms ending in

rings. The dredge-rope is made fast to one of these rings, while the

other is held only by a "stopping" of yarn, which gives way if the

dredge should catch on a rock, and permits it to be dragged sideways off

the obstruction. The size and weight of the dredge may vary according to

the depth at which it is to be used and the power available for working

it. A convenient size for use with a small sailing boat at moderate

depths has a frame 20 by 5 inches.

Apart from dredging, many specimens from moderately deep water may be

picked out from among the "rubbish" brought up on fishermen's lines or

by the trawl, and various Crustacea besides the edible species find

their way into Lobster and Crab pots. The true deep-sea fauna is, for

the most part, only to be reached by specially-equipped expeditions,

although specimens from great depths are occasionally obtained during

the operations for the repair of submarine telegraph cables.

The floating animals of the surface of the sea are to be captured by

means of the tow-net. This consists of a conical bag of muslin,

cheese-cloth, or, best of all, silk "bolting-cloth," attached to a

galvanized iron-ring of one or two feet in diameter, and having a zinc

can or a strong glass jar fixed to the narrow end. The ring is attached

by three equidistant cords to the towing line, and the net is towed

slowly at or near the surface of the sea. When taken on board, the

contents of the can are emptied into a jar of sea-water for examination.

The tow-net is best used when there is only enough way on the boat to

keep the net from sinking; if towed more rapidly, delicate organisms are

apt to be crushed by the pressure of the water, or the net itself may be

burst. The use of unnecessarily fine nets should be avoided. A

fine-meshed net may not capture a single specimen of the larger

Crustacea, even though these may be swarming in the water through which

it is drawn.

By weighting the tow-net it may be used at various depths to capture the

floating animals of mid-water. When it is so used, however, it is

impossible to tell from what depth any particular specimen may have

come, since it may have been captured during the hauling in of the net.

For more precise investigations in deep water, "closing tow-nets" of

various types have been devised, which can be opened by a "messenger"

sent down the line when the net has reached the desired depth, and

closed again by another "messenger" before it is hauled in.

A simple method that has proved very successful for collecting small

Crustacea living on a sandy bottom in shallow water is to employ a light

tow-net with a cane ring, and with a heavy sinker attached to the towing

line at a distance of a few feet in front of the net. As the sinker is

dragged along the bottom, the net floats up behind it, and catches small

animals stirred up by its passage.

For collecting the smaller fresh-water Crustacea--Water-fleas and the

like--a small muslin ring-net may be used in ponds and ditches. The

plankton of the open water of lakes is best obtained by means of a

tow-net like that described above for use in the sea.

The interesting blind species known as "Well Shrimps" are to be looked

for in the water of springs and wells. In wells fitted with a pump,

Professor Chilton found that "the Crustacea are often brought up most

abundantly when pumping is first commenced, and that jerking the handle

of the pump somewhat violently is often more successful than pumping at

the ordinary rate." In disused open wells, they may be trapped by

baiting a muslin ring-net with a piece of stale meat or fish, and

pulling it up rapidly after it has remained in the well for a few hours.

The subterranean waters of caves have yielded many curious species in

various parts of the world. For the capture of species living in the

deep water of large lakes, a special form of dredge has been devised

with runners to prevent it from sinking into the soft mud, while the

mouth of the net is raised a few inches above the bottom.

For preserving Crustacea the best medium to use is 70 per cent. alcohol.

Strong spirit diluted with a little less than one-third its bulk of

water gives about the required strength. If too strong spirit is used,

the specimens tend to be hard and brittle, and delicate organisms become

shrivelled. Methylated spirit as sold in the shops in this country

contains mineral naphtha, and turns milky when water is added, so that

it is unsuitable for preserving specimens. Methylated alcohol without

naphtha can be bought, by permission of the Inland Revenue authorities,

but only in considerable quantities at a time.

Formalin is very cheap and readily obtained, but it is much less

suitable than spirit for most Crustacea, as it tends to make them stiff

and fragile, and small forms containing much lime, such as Cumacea, may

become decalcified. For Crustacea collected by the tow-net, however,

formalin gives good results. A few drops of strong formalin, added to

the water into which the tow-net has been washed, kills the animals in a

few minutes. After they have sunk to the bottom, the liquid may be

poured off and replaced by formalin diluted with sea-water (for marine

plankton), or by a mixture of formalin and spirit. The most suitable

strength of formalin varies with different organisms, but 5 per cent.

(_i.e._, 1 part of commercial formalin to 19 parts of water) is perhaps

most generally useful.

Crabs, Prawns, and the like, if put alive into strong spirit, may throw

off some of their limbs, or else become so rigid that these break on

the slightest manipulation. This may often be avoided by killing the

animals in weak spirit (30 per cent. or less) before preserving in

strong spirit. Marine species may also be killed by placing them in

fresh water, care being taken not to allow them to remain in it longer

than is necessary, as it causes distortion of the membranous appendages.

The larger Crabs, Lobsters, and the like, may be preserved dry, although

in this state they are unsuitable for examination of the more delicate

appendages. The carapace should be detached, and the soft parts cleaned

away as far as possible, a bent wire being used, if necessary, to remove

the flesh from the legs. The specimens should be dried in the shade, to

preserve as much as possible of the natural colour.

With specimens intended for permanent preservation in spirit, the use of

corks should be avoided, as they discolour the spirit, and ultimately

the specimens. Small specimens are most conveniently kept in glass tubes

closed with a piece of clean elder-pith (not cotton-wool), and placed,

upside down, in a bottle of spirit. Labels to be placed inside the tubes

are best written with Indian ink, and allowed to dry before immersion in

the spirit.

II. NOTES ON BOOKS

The literature of Carcinology is bewildering in its extent, and is for

the most part scattered through the volumes of scientific periodicals

and the publications of learned societies in most of the languages of

Europe. A guide to the current literature is provided by the _Zoological

Record_, the latest volume of which, relating to the year 1909,

enumerates no fewer than 337 papers dealing wholly or in part with this

group of animals.

The following short list of books in the English language may be of some

help to the beginner. Most of them give references to the literature

which will provide the necessary guidance towards a further study of the

subject.

GENERAL WORK

_Huxley, T. H._ The Crayfish: an Introduction to the Study of

Zoology. International Science Series, vol. xxviii. London, 1880.

_Stebbing, T. R. R._ A History of Crustacea: Recent Malacostraca.

International Science Series, vol. lxxiv. London, 1893.

_Calman, W. T._ Crustacea. A Treatise on Zoology, edited by Sir Ray

Lankester. Part vii., fascicle iii. London, 1909.

_Smith, G._, and _Weldon, W. F. R._ Crustacea. The Cambridge

Natural History, vol. iv. London, 1909.

_Lister, J. J._ Crustacea, in "A Student's Textbook of Zoology," by

Adam Sedgwick. Vol. iii. London, 1909.

BRITISH CRUSTACEA

_Baird, W._ The Natural History of the British Entomostraca. (Ray

Society.) London, 1850.

_Bell, T._ A History of the British Stalk-eyed Crustacea. London,

1853.

_Spence Bate, C._, and _Westwood, J. O._ A History of the British

Sessile-eyed Crustacea. 2 vols. London, 1863 and 1868.

_Brady, G. S._ A Monograph of the Free and Semiparasitic Copepoda

of the British Islands. (Ray Society.) 3 vols. London, 1878-1880.

These works, although still valuable, and indeed indispensable, are now

more or less out of date. A list of British Malacostraca (except

Amphipoda) will be found in Mr. Stebbing's volume mentioned above.

_Sars, G. O._ An Account of the Crustacea of Norway. Vol. i.,

Amphipoda, 1890-1895. Vol. ii., Isopoda, 1896-1899. Vol. iii.,

Cumacea, 1899-1900. Vols. iv. and v., Copepoda, 1903 (in progress).

Christiana and Bergen.

A very large proportion of the British species in the groups mentioned

are described and figured in this splendid series of volumes. The text

is in English.

_Norman, A. M._, and _Scott, T._ The Crustacea of Devon and

Cornwall. London, 1906.

_Webb, W. M._, and _Sillem, C._ The British Woodlice. London, 1906.

Memoirs of the Liverpool Marine Biology Committee, edited by

Professor _W. A. Herdman_. A useful series of monographs on the

structure and life-history of common British marine animals and

plants. The following relate to Crustacea:

Memoir VI. Lepeophtheirus and Lernaea (Parasitic Copepoda). By _A.

Scott_. 1901.

Memoir XII. Gammarus (Amphipod). By _M. Cussans_. 1904.

Memoir XIV. Ligia (Isopod). By _C. G. Hewitt_. 1907.

Memoir XVI. Cancer (Edible Crab). By _J. Pearson_. 1908.

Descriptions of all the British species of Barnacles will be found

in _Darwin's_ "Monograph of the Sub-class Cirripedia." (Ray

Society.) 2 vols. London, 1851-1854.

INDEX

Abdomen of Lobster, 6

Abyssal fauna of lakes, 185

Acanthephyridae, 268

Acorn-shells, 41

_AEga_: in Sponges, 210;

parasitic on fish, 219

_AEger_, 267

_AEglea_, 181

Air-breathing Crabs, 188

_Albunea_, 102

Alcock, A.: on habits of _Ocypode_, 105;

on temperature of sea, 120;

on eyes of deep-sea Crustacea, 124;

on colour in deep-sea Crustacea, 127;

on luminosity of deep-sea Crustacea, 125, 126;

on eggs of deep-sea Prawn, 130;

on _Nephrops_, 132;

on habits of _Coenobita_, 194, 195

Allen, E. J., on Mackerel fishery, 251

Alpheidae, 211

American Lobster, 32

Amphibious Crustacea, 104, 188

Amphipoda, 52;

seashore, 95, 107;

plankton, 145;

terrestrial, 189;

fresh-water, 172;

in Sponges, 210;

on Jellyfishes, 212;

and Hermit Crabs, 215;

parasitic, 223;

wood-boring, 255

_Amphithoe_, 95

_Anaspides_, structure and fossil allies, 264

Andrews, C. W.:

on Land Crabs, 190;

on habits of _Coenobita_, 195;

on habits of _Birgus_, 197, 198

_Anomalocera_, 150

Anomura, 60;

fresh-water, 181

Anostraca, 36;

habits, 162, 164

Antennae of Lobster, 8, 14;

use in respiration in _Corystes_, 100;

in _Albunea_, 102

Antennule of Lobster, 8, 14

Ants, Woodlice living with, 205

_Apseudes_, 50

_Apus_, 36;

habitats, 161;

occurrence in Britain, 162;

habits, 163;

haemoglobin in, 165;

fossil allies of, 260

Appendages of Lobster, 8;

of Trilobites, 259

_Aratus_, 189

_Argulus_, 41

Aristotle on Shrimp living with Mollusc, 218

_Armadillidium_, 203

_Artemia_:

larvae of, 81;

habitat, 164

Arthropoda, 2;

classification, 204

_Asellus_, 172;

destroying fishing nets, 253

Astacidae, 176

_Astacoides_, 178

_Astacopsis_, 177;

used for food, 243

Astacura, 60

_Astacus_:

habits, 174;

young, 76;

distribution, 177;

used for food, 241

Asymmetry of Lobster, 29

Atyidae, 179;

used for food, 248

Autotomy, 113;

in Lobster, 30

Baikal, Lake, 182

_Balanus_, 42;

larvae, 83;

habits, 114;

used for food, 237;

cultivated for manure, 250

Barnacles, 41;

development, 83;

seashore, 114;

of high seas, 155;

on Whales, Turtles, and Crabs, 209;

parasitic, on fish, 235;

used for food, 237;

cultivated for manure, 250;

fossil, 261

_Bathynomus_, 131

Beach-fleas, 107

Bell, T., on development of Land Crabs, 193

"Berry," Lobster in, 28

Bipolarity, 132

_Birgus_, 94;

habits and structure, 195;

breeding habits, 199.