Crayfish

“ Crayfishes are caught in various ways; sometimes the fisherman simply wades in the water and drags them out of their burrows; more commonly, hoop-nets baited with frogs are let down into the water and rapidly drawn up, when there is reason to think that crayfish have been attracted to the bait; or fires are lighted on the banks at night, and the crayfish, which are attracted, like moths, to the unwonted illumination, are scooped out with the hand or with nets. ”

“ Accepting it for the moment, it is obvious that the crayfish is unquestionably an animal,—as much an animal as the vole, the perch, and the pond-snail, which inhabit the same waters. Moreover, the crayfish has, in common with these animals, not merely the motor and digestive powers characteristic of animality, but they all, like it, possess a complete alimentary canal; special {229} apparatus for the circulation and the aëration of the blood; a nervous system with sense-organs; muscles and motor mechanisms; reproductive organs. ”

“ If a living crayfish is taken out of the water, it will be found that, as the water drains away from the branchial cavity, bubbles of air are forced out of its anterior opening. {81} Again, if, when a crayfish is resting quietly in the water, a little coloured fluid is allowed to run down towards the posterior opening of the branchial chamber, it will very soon be driven out from the anterior aperture, with considerable force, in a long stream. ”

“ In a piece of land converted into a crayfish farm, in which the white-clawed crayfish existed naturally in great abundance, 300,000 red-clawed crayfish were introduced in the course of five years; nevertheless, at the end of this time, no intermediate forms were to be seen, and the “pieds rouges” exhibited a marked superiority in size over the “pieds blancs.” M. Carbonnier, in fact, says that they were nearly twice as big.
On the whole, the facts as at present known, seem to incline rather in favour of the conclusion that A. torrentium and A. nobilis are distinct species ”

“ Thus we see that the crayfish has a jointed and segmented body, the rings of which it is composed being very obvious in the abdomen, but more obscurely traceable elsewhere; that it has no fewer than twenty pairs of what may be called by the general name of appendages; and that these appendages are turned to different uses, or are organs of different functions, in different parts of the body. The crayfish is obviously a very complicated piece of living machinery. But we have not yet come to the end of all the organs that may be discovered even by cursory inspection. ”

“ CHAPTER III. THE PHYSIOLOGY OF THE CRAY­FISH—THE MECH­A­NISM BY WHICH THE LIV­ING OR­GAN­ISM AD­JUSTS IT­SELF TO SUR­ROUND­ING CON­DI­TIONS AND RE­PRO­DUCES IT­SELF. If the hand is brought near a vigorous crayfish, free to move in a large vessel of water, it will generally give a vigorous flap with its tail, and dart backwards out of reach; but if a piece of meat is gently lowered into the vessel, the crayfish will sooner or later approach and devour it. ”

“ The Crayfish or Crawfish (Fr.: Écrevisse) , or river lobster, is a long-tailed, ten-footed crustacean resembling the lobster, and similar to it in its habits. It was considered a delicacy by the Greeks and Romans, and was eaten by them seasoned with pepper and other condiments. Crayfish are best preserved alive by keeping them in baskets with fresh grass or plants such as the nettle, or in a vessel containing only a slight depth of water. As the crayfish requires a quantity of air, the water should be frequently renewed.
141.—EEL BROTH. (Fr.—Bouillon d'Anguille.) ”

“ There is no evidence that our crayfish has been purposely introduced by human agency into Great Britain; and from the mode of life of crayfish and the manner in which the eggs are carried about by the parent during their development, transport by birds or floating timber would seem to be out of the question. ”

“ The constant secretion of the lime necessary to make these shells is so exhausting to the youthful crayfish that only a small number ever grow up. In America, where a large freshwater crayfish nearly a foot long is found, its burrowing habits are a serious nuisance, especially in the dykes of the Mississippi. In those streams from which these interesting little creatures have entirely disappeared it might be worth while to introduce the large Continental crayfish. ”

“ Both salt and fresh water crayfish are taken in large quantities. The latter, which are very large, are almost invariably captured by the women, who have to dive for them, and the former are taken in traps baited with flesh, much like our own lobster-pots. ”

“ In general appearance they are not very unlike the adults. They grow very rapidly at this stage. As the animal is enclosed in a hard shell, growth can only take place during the period just following the molt, for the crayfish casts its skin periodically, and it is while the new shell is forming that the animal does its growing. The crayfish when it molts casts not only the exoskeleton, but also the lining of part of the alimentary canal. After the females have hatched their young many die in the shallow pools, in which places the dried-up skeletons are noticeable during the summer months. ”

“ Some of the Australian crayfishes (fig. 76) attain a foot or more in length, and are as large as full-sized lobsters. The genus Engæus of Tasmania comprises small crayfish which, like some of the Cambari, live habitually on land, in burrows which they excavate in the soil.
New Zealand has a peculiar genus of crayfishes, Paranephrops, a species of which is found in the Fiji Islands, but none are known to occur elsewhere in Polynesia. ”

“ We shall see, by-and-by, that there are some exotic crayfish which habitually live on land, and perish if they are long submerged in water.
With respect to the internal structure of the crayfish, there are some points which cannot escape notice, however rough the process of examination may be.
FIG. 5.—Astacus fluviatilis.—A male specimen, with the roof of the carapace and the terga of the abdominal somites removed to show the viscera (nat. size) :—aa, antennary artery; ag, anterior gastric muscles; amm, adductor muscles of the mandibles; cs, cardiac portion of the stomach; gg, green glands ”

“ Crayfishes may be taken by a net baited with dead fish, or they may be caught in a trap made from a box with ends which open in, and baited with dead fish or animal refuse of any sort. This box should be placed in a pond or stream frequented by crayfish. If possible the student should study the living animal and observe its habits. Crayfish which are to be kept alive should be placed in a moist chamber in a cool place. ”

“ With respect to the second point for consideration, it is to be remarked that, in the temperate regions of the world, the crayfishes are by far the largest and strongest of any of the inhabitants of freshwater, except the Vertebrata; and that while frogs and the like fall an easy prey to them, they must be formidable enemies and competitors even to fishes, aquatic reptiles, and the smaller aquatic mammals. ”

“ The hypothesis that the body of the crayfish is made up of a series of homologous somites and appendages, and that all the tissues are composed of nucleated cells, might be only a permissible, because a useful, mode of colligating the facts of anatomy. The investigation of the actual manner in which the evolution of the body of the crayfish has been effected, is the only means of ascertaining whether it is anything more. And, in this sense, development is the criterion of all morphological speculations. ”

“ When the young crayfish is ready to be hatched, the egg case splits into two moieties, which remain attached, like a pair of watch glasses, to the free end of the pedicle of the egg (fig. 8, A; ec) . The young animal, though very similar to the parent, does not quite “resemble it in all respects,” as Roesel says. For not only are the first and the last pairs of abdominal limbs wanting, while the telson is very different from that of the adult; but the ends of the great chelæ are sharply pointed and bent down into abruptly incurved hooks, which overlap when the chelæ are shut (fig. 8, B) . ”

“ The specimens were very plentiful around Boiling Springs, a place where one of the cold, underground rivulets of the region breaks through the rocks in the bottom of the stream.
In a clear, rocky stream, [B] shallow in most places, flowing between high hills, about four miles northwest of Springfield, crayfish were found in abundance. The smaller and by far the more numerous species was C. neglectus. The animals were very active, darting from stone to stone when disturbed, but usually remaining under cover but a short time. ”

“ For the most part, however, the crayfish lurks in coral caves, sweeping a considerable frontal radius with ever-shifting antennae—not in pride or conceit of their beautiful tints and wonderful mechanism, but with a pitiful apprehension of danger, for the admirers of the creature are many and ever so much in earnest—the earnestness of unceasing voracity. ”

“ Then would the crayfish loosen their hold, roll over on their backs, flap their tails very briskly, and start off with amazing rapidity for short country walks, speedily to be captured and consigned to the recesses of a receptacle, bearing a suspicious resemblance to Madame Couttet’s work-basket. ”

“ To put the matter in its most general shape, the body of the crayfish is a sort of focus to which certain material particles converge, in which they move for a time, and from which they are afterwards expelled in new combinations. The parallel between a whirlpool in a stream and a living being, which has often been drawn, is as just as it is striking. ”

“ I learned to-day the way to procure the crayfish as the natives do. In a swamp you see a hole with earth thrown up, much in the way that you see it with the large worms on the sea shore. You must put in your arm and scrape with your hand till you find it perhaps two feet down. It is like a small, very small lobster, and can bite very smartly. ”

“ Beside these internal structures, the most noticeable are the large masses of flesh, or muscle, in the thorax and abdomen, and in the pincers; which, instead of being red, as in most of the higher animals, is white. It will further be observed that the blood, which flows readily when a crayfish is wounded, is a clear fluid, and is either almost colourless, or of a very pale reddish or neutral tint. Hence the older Naturalists thought that the crayfish was devoid of blood, and had merely a sort of ichor in place of it. But the fluid in question is true blood ”

“ The Californian crayfish is larger and somewhat differently coloured, the undersides of the forceps particularly presenting a red hue. The limbs, and especially the forceps of the males, are relatively longer; the chelæ of the forceps have more slender proportions; the areola is narrower relatively to the transverse diameter of the carapace (fig. 61, C) . More definite distinctions are to be found in the rostrum, which is almost parallel-sided for two-thirds of its length, then gives off two strong lateral spines and suddenly narrows to its apex. ”

“ They grow very fast, and this makes it necessary for the youthful crayfish to "moult" or shed their shells eight times in their first twelvemonth of life, as the shell is rigid and does not grow with the body. ”

“ The crayfish, as we have seen, avoids light; and the slightest touch of one of its antennæ gives rise to active motions of the whole body. In fact, the animal’s {110} position and movements are largely determined by the influences received through the feelers and the eyes. These receive their nerves from the cerebral ganglia; and, as might be expected, when these ganglia are extirpated, the crayfish exhibits no tendency to get away from the light, and the feelers may not only be touched, but sharply pinched, without effect. ”

“ Is its colour suited to live in clear or muddy water? Define protective colouration.
52Habits.—Does the crayfish walk better in water or out of it? Why? Does it use the legs with the large claws to assist in walking? Do the swimmerets (under the abdomen) move fast or slow? (Observe it from below in a large jar of clear water.) What propels it backward? Forward? Does the crayfish move at a more uniform rate when swimming backward or forward? Why? In which way can it swim more rapidly? Do the big legs with claws offer more resistance to the water while it is swimming backward or forward? ”

“ Having got thus far, the crayfish rests for a while, and then the agitation of the limbs and body recommences. The carapace is forced upwards and forwards by the protrusion of the body, and remains attached only in the region of the mouth. The head is next drawn backwards, while the eyes and its other appendages are extracted from their old investment. Next the legs are pulled out, either one at a time, or those of one, or both, sides together. Sometimes a limb gives way and is left behind in its sheath. ”

“ In many animals allied to crayfish, the young, when it has reached a stage in its development, which answers to this, undergoes rapid changes of outward form and of internal structure, without making any essential addition to the number of the appendages. The appendages which represent the antennules, the antennæ, and the mandibles elongate and become oar-like locomotive organs; a single median eye is developed, and the young leaves the egg as an active larva, which is known as a Nauplius. ”