CHAPTER II

SPECIMENS

Collecting

To study adequately any branch of natural history, it is essential to have specimens. Many exemplary forms of Crustacea are not difficult to obtain. Representatives of the two highest orders in the group, the crab, the lobster, the prawn, the shrimp, are exceedingly familiar, as these creatures lie on the fishmonger's board, or are brought to table for food. When the eatable parts have been consumed or otherwise removed, the débris is still of value for mental nourishment. This refuse may be made to yield more profit and pleasure than many a costly collection which can only be viewed intact. By carefully separating the constituent parts of the head, the trunk, and the tail, in each of the crustaceans above mentioned, and comparing them piece by piece, the beginner will be able to give himself a cheap but invaluable lesson. He will be surprised at first to detect likenesses in the corresponding parts of animals externally very distinct, and afterwards he will be surprised at the differences in the corresponding parts of animals which he has learned to regard as closely connected. As his range of study widens, he will find relationships established between forms which, to any one unacquainted with the intermediate links, must seem to have absolutely nothing in common. For instance, while examining the gills of a lobster, he may chance to observe some small orange-coloured specks, and may rightly conjecture that these are parasitic animals. But it is scarcely conceivable that any amount of genius would

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enable a man to discern, from a comparison of the lobster alone with its entomostracan parasite, that they are alike crustaceans, which is, nevertheless, known to be the case. In a dishful of prawns it may often be noticed that one or two of the finest have the head swollen on one side, as if the creature were suffering from a face-ache. There is no special reason to suppose that the prawn thus affected is suffering any great inconvenience. It is merely lending the shelter of its carapace to a family of isopod crustaceans. Comfortably ensconced in the bulging cheek-piece will be found a misshapen animal of no inconsiderable size, in general laden with innumerable eggs, and accompanied by a far smaller partner, the father of the brood, symmetrical in form, and retaining some of the freedom of movement which belongs to the young when first hatched, but which the mother has entirely resigned. Thus the zoology of the breakfast table will supply examples of three very distinct orders. These examples are none the less curious because they happen to be common. Any one who is content to examine them with care will thereby lay a simple and solid foundation for all subsequent study in the realm of carcinology.

The novice, however, need not be dependent on the fishmonger for specimens. In cellars, gardens, hedges and ditches, under flat stones, in dry moss, among moist dead leaves, in the loosened decaying bark of trees, crustaceans are to be met with almost everywhere. These are the so-called wood-lice, including those known by the trivial names of Pill-bugs and Slaters, Millepedes, and Carpenters. One species, small and white and slow in movement, is frequently to be found in ants' nests, and seemingly never elsewhere. All this set of animals, though air-breathing and living on land and often possessing great agility, belong to the Isopoda in common with the marine species above mentioned that leads its apathetic life within the carapace of the prawn.

From almost every little brook and pond in England the amphipod, Gammarus pulex, and the isopod, Asellus aquaticus, may be fished without difficulty and without

any stint of numbers. Less commonly the innocent wellshrimps, which are also amphipod crustaceans, may be obtained from wells. It may be proper to mention that the well-shrimp is not poisonous, and that it flourishes in water which is perfectly wholesome. A different view of its character is probably entertained by many owners of wells, who are on that account unwilling to mention or acknowledge its presence. From stagnant ponds various species of Entomostraca may be obtained in vast abundance. Some of the Phyllopoda are found only in brine pools. The brine shrimp, Artemia, breeds in vast numbers in the mud of the great Salt Lake of Utah. In South America one of the Ostracoda very singularly dwells on the leaves of a plant. The river crayfish and crustaceans parasitic on freshwater fish are pretty widely distributed. Highest in known range of all the Crustacea are the Isopods and Amphipods taken by Mr. Whymper at a height of 13,300 feet on the Great Andes of the Equator. In many parts of the world there are land-crabs, but none of these live in the British Isles. This is referred to as follows in the 'Narrative of the Cruise of the Challenger.' In describing the visit to Ascension Island in the South Atlantic Ocean, the writer says:-

and

'Land-crabs swarm all over this barren and parched volcanic islet. They go down to the sea in the breeding season; they climb up to the top of Green Mountain, the larger ones steal the young rabbits from their holes and devour them. It always seems strange to an English naturalist to see crabs walking about at their ease high up in the mountains, although the occurrence is common enough and not confined to the tropics. In Japan a crab is to be met with walking about on the mountain high roads far inland, at a height of several thousand feet, as much at home there as a beetle or a spider, and crabs of the same genus (Thelphusa) live inland on the borders of streams in Greece and Italy.'

France and Germany, as well as England, have reason to regret that the sunny south should have a monopoly of these land or river crabs, for they are delicate eating, and,

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15

as writers of the sixteenth century inform us, they are much sought after for the tables of the Pope and cardinals.

From what has been said it will be seen that those who live inland enjoy no inconsiderable opportunities of observing crustaceans of various kinds, dead or living. The common and easily obtainable specimens will, as a rule, not be of the same species in different parts of the world, but they will often belong to the same or closely allied genera, and they will in any case afford similar facilities for study. The traveller would do well to remember that kinds easy to collect abroad or cheap to buy in foreign markets will probably be rare in his own country, and that therefore preserved specimens may be of future value to himself or acceptable to his friends at home.

Passing, however, from inland resources to those of the sea coast, the student will find an enormously greater and an almost bewildering variety of forms to engage his attention. Shore-crabs and hermit-crabs are often obtrusively conspicuous, as also are the operculate cirripedes with their sharp-edged shells coating large surfaces of rock. When a flat stone is lifted, not unfrequently a small specimen of the edible crab may be seen nestling in the mud. If the position is chosen in order to gratify the sense of smell, one would be inclined to adapt the words of the poet to the situation, and say that crabs want but little here below, but want that little strong. Clinging to the under surface of a stone, a group of the broadclawed Porcellana, the hairy porcelain crab, will often be found. They try to look as if they were not there, or they endeavour to slidder rapidly away. If one is seized by the claw, it will adhere as tenaciously as it can to the rock, and sometimes end the unequal contest by relinquishing the claw and running off without it. The lobsterlike Galathea, under similar circumstances, is ready either to fight or run, a very Achilles for courage and speed. Specimens of the masked crab and of various spider crabs, and of others not commonly found alive upon the shore, are often to be met with upon it when an obliging gale of wind has thrown their carcases landward. The common

shrimp will sometimes attract attention by making an abrupt spring, after which it sinks softly into the moist sand, from which its imitative colouring makes it barely distinguishable. The stretches of sand on the shore, which to unobservant or inexperienced eyes might seem quite barren and deserted, are often teeming with crustacean life. The upper and driest zone will be riddled with the burrows of the sand-hopper. Lower down several other species of amphipods lie at a very small depth beneath the surface. Little biting carnivorous isopods are there, and occasionally others that are vegetarians. In some localities Cumacea can be found, but never very far from the waves, nor, when they are present, must it be expected that these animals will make a striking feature in the landscape. They are remarkably unobtrusive. Where rocks and

rock-pools and various kinds of seaweed abound, and especially on sheltered coasts, a very large number of species of amphipods and isopods may be obtained, these being in most instances distinct from those found in the sand. Here is to be seen Orchestia, the shore-hopper, a near ally of the sand-hopper, Talitrus. Here are two of the marine species of Gammarus, and examples of their cousins Melita and Mara, all of which, when on land, slip or wriggle along on their sides, and have in consequence been irreverently spoken of as 'scuds.' Many other forms, including some of the Caprellidæ or skeleton-shrimps, can be obtained by examining tufts of the finely branched seaweeds. At the lowest ebb of the spring tides, a day or two after new moon or full moon, species may be obtained which are rarely or never procurable higher up on the shore. Several of the isopods, however, may be taken, independently of the lowness of the tide, roaming among the coarser weeds, and mimicking in various ways the colours around them. The rocks which look least interesting, having no vegetation except the short black crumbling foliage of the Lichina pygmæa, supply the curious Campecopea hirsuta, an isopod easily to be confounded with the leaves of the tiny plant which shelters it. Found among cirripedes at low tide, however, it displays much brighter