VARIOUS LODGINGS

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colouring. Where wooden piles have been driven into the shore within tide-marks, the part which the water reaches is almost sure to be very soon attacked and taken possession of by two or three very distinct crustaceans, the two constant companions being the strange amphipod Chelura terebrans, with a name signifying the boring claw-tail, and a perhaps equally mischievous isopod, known as Limnoria lignorum, or the Gribble. With these is frequently associated one of the cheliferous isopods, the species Tanais vittatus in England, and Tanais filum in America, not concerned, it may be, in making the excavations, but only using them when made. Some Amphipoda and Isopoda shelter themselves in sponges and some in the branchial sacs of Ascidians.

Many free-living Copepoda may be obtained in rockpools and by washing seaweeds, others from various Ascidians. Those parasitic Copepoda, which are commonly known as fish-lice, may often be procured by examining fishes when first brought to shore, and before they have been prepared for display on the fishmonger's board. New species of Crustacea have sometimes been discovered by the examination of the contents of a fish's stomach. This same repository will also occasionally yield good specimens of already known species.

The Cirripedes are all marine, most of them impatient even of brackish water, although one species, Balūnus improvisus, Darwin, will live contentedly for some time in water that is quite fresh. Several species are obtainable between tide-marks. Many attach themselves to the submerged sides of ships, and to other floating objects. Some make their home in sponges, corals, or shells, and in consequence specimens not sought for their own sake are frequently distributed by the commerce of which their dwelling-places are the more direct object.

For the Gigantostraca collectors in England must content themselves either with fossil or with imported species. In New England, the horseshoe crab, Limulus polyphemus, may be had at or just below low water.

By availing himself, then, of those Crustacea which

live on land or in shallow waters, or on the coast, and of those specimens which are brought to shore either as or in connection with articles of food, the student may obtain a thoroughly representative collection. Closely as all the easily accessible localities and resources have been already searched and examined, even from among them he will find it still possible to add new species to the long roll of those hitherto known. In many of the forms that are common and abundant, and that have long been familiar to science, he may, by diligent observation, find features of great interest that have heretofore escaped notice. One discovery he will almost certainly make, that the objects of his study do not deserve the epithets of contempt and disgust so freely lavished upon them by the ignorant. At every step he will be increasingly charmed by the striking characters which different species exhibit, by the delicate grace or the intricate mechanism of the separate parts, and by the marvellously varied adaptation of the different organisms to their diverse modes of life.

It is, however, in the waters of the ocean, from the surface down to the abyssal depths, that the vast majority of the Crustacea are to be found. Of the lower limits of the so-called bathymetrical distribution a good general idea may be formed from the results of the dredging and trawling carried on by the Challenger, during a voyage of nearly seventy thousand miles. Of the Brachyura indeed, only a single specimen of a single species was taken so low down as 1,875 fathoms. Mr. Miers, who named it Ethusa (Ethusina) challengeri, says: "This is the greatest depth at which any Brachyurous crustacean was taken by the expedition, and also, I believe, the greatest hitherto recorded for any species of crab.' It was not, perhaps, to be expected that members of the highest order in the class would either need or condescend to penetrate into the very lowest regions, where light and heat and vegetation, not to speak of cheerful society, must at the best be very scanty and extremely scarce. The very genus Ethusa, with its sub-genus or neighbouring genus Ethusina, seems to apologise for frequenting levels beneath its

SPECIMENS IN THE DEEP SEA

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natural rank by including the forms which, as Mr. Miers observes, evince the greatest degree of degradation from the Brachyuran type." It approaches in fact the group which till recently held a distinct position under the name of the Anomura. Of these Dr. Henderson observes that they occupy an intermediate position between the Macrura and the Brachyura, in regard to the limit of depth at which they are found, the more highly specialised forms being, like the Brachyura, found in shallow water and at moderate depths, whereas the more primitive macruran types extend to the abysses of the ocean. The single and singular specimen on which the species Tylaspis anomala, Henderson (see Plate VII.), was established, 'came from the greatest depth at which any anomurous crustacean was taken by the Challenger,' the depth in question being 2,375 fathoms. In the Macrura two genera, Benthesicimus and Gennădas, instituted by the late Mr. Spence Bate, descend to 3,050 fathoms, and have nowhere been found dwelling with less than 300 fathoms of water above them. It is not perhaps surprising that most of the specimens were brought up in a soft, pulpy, and collapsed condition,' for it is calculated that each perpendicular mile, that is, each 880 fathoms of water, exercises a pressure of a ton upon each square inch of an animal's surface. As long as the fluids within correspond with those outside the body, there is a state of comfort and efficiency, but when this equilibrium is suddenly destroyed, uot only a crustacean but any other creature is likely to feel weak and discomposed.

6

Of the Schizopoda Boreomysis obtusata, Sars, was taken from a depth of 2,740 fathoms. On the other hand the Stomatopoda are content with far less profound explorations. Mr. W. K. Brooks reports that they are usually found in very shallow water, and with the exception of the specimen of Squilla leptosquilla, taken in the trawl by the Challenger in the Celebes Seas from a depth of 115 fathoms, and a specimen of Lysiosquilla armata, which Mr. S. I. Smith found in the stomach of a Lopholatilus from 120 fathoms, they are all from very moderate depths.' The Challenger

found a cumacean as low down as 2,050 fathoms, but some years earlier the Swedish Spitzbergen expedition obtained the appropriately named Diastylis stygia from the still lower deep of 2,600 fathoms. The Isopoda extend down to 2,740 fathoms, the Amphipoda possibly, but by no means certainly, to 2,500. Among the Entomostracans, a Phyllocarid species came from 2,550 fathoms, Ostracoda from 2,750, the strange copepod, Pontostratiōtes abyssicòla, Brady, from 2,200, and a parasitic copepod, Lernæa abyssicola, was attached to a deep-sea fish brought by the trawl from 2,400 fathoms. Lastly, of the Cirripedes the great Scalpellum regium was dredged from a depth of 2,800 fathoms, the character of these animals giving more certainty than can be had with free-swimming Crustacea, that the specimens actually came from the depth assigned. In the use of trawls and dredges with open mouths, there is always a chance that specimens may be captured in the course of lowering or hauling in the instrument, instead of while it is being dragged along the ocean floor. By this means the record of the occurrence of specimens at astonishing depths is left open to some question. Yet on the whole there is fair reason to believe that most of the principal groups of Crustacea have representatives capable of supporting existence in regions of dense gloom, with a temperature icily cold, and under a column of water from two to three miles in height. Many species, indeed, of the Crustacea show a preference for a frigid climate, since where this condition prevails their swarms are far vaster and their bodies more bulky and solid than in waters less cold. These Polar forms, therefore, find no inconvenience, but the reverse, in the unheated temperature of the great depths, and though probably many of them could not possibly pass the tropical waters at or near the surface, far down there is a suitable water-way for them from one pole of the earth to the other.

It is rather the task of national expeditions than of any private collector to procure the exceptional forms. which the remotest abysses of the sea have yielded and may be expected still from time to time to yield. There

METHODS OF CAPTURE

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are, however, unstinted riches of natural history which the ordinary student may obtain with comparatively simple means. By the use of the towing-net from a boat, especially after sunset in warm and calm weather, numerous larval forms of Crustacea are to be obtained, as well as adult forms of various orders. By dredging in a few fathoms, or even in a few feet, of water, species enough to occupy weeks and months of study may often readily be secured. For this work sheltered bays and inlets are favourable. When the dredge brings up apparently nothing but rugged pebbles and the worn shells of departed molluscs, these are not to be despised. Among them may be found the little crabs of the genus Ebalia, at the first glance perhaps rejected as if pebbles themselves. Rare Tanaids may come creeping out of the crevices of an old oyster shell. When sea-weeds are brought up in the dredge, they are not to be cast aside after a hasty examination as unproductive. They should be placed in a vessel of shallow water, and, though the crafty inhabitants lie close, they will eventually come forth. Sand and muddy ooze scraped from the bottom requires to be passed through a sieve or stirred about in a pailful of sea-water. After the stirring, and before the animals have time to regain the sand, the water must be poured off through a muslin bag which will retain the desired specimens. Some species, besides the edible ones, may be obtained by a sort of systematic fishing. A dead crab, for instance, let down in a lobster-pot, will attract one species or another according to the locality, the clan trooping to the feast in hundreds and thousands till they have consumed every par ticle of the dainty repast. The voracity, indeed, of some among the smaller Crustacea is such, and their numbers in some places so enormous, that they have been known in a single night to clear all the flesh off a dead seal. To such appetites almost any carrion is a sufficiently alluring bait. There is little need for surprise, under the circumstances, at the label on certain museum specimens, irtimating that they were 'pulled off the head of a bear let down to the bottom to be cleaned.' Some of the Amphipoda attack the