FIG. 8.—Astacus fluviatilis.—A, two recently hatched crayfish attached to one of the swimmerets of the mother (× 4). pr, protopodite; en, endopodite; and ex, exopodite of the swimmeret; ec, ruptured egg-cases. B, chela of a recently hatched crayfish (× 10).
That most careful naturalist, Roesel von Rosenhof, says of the young, when just hatched:—
“At this time they are quite transparent; and when such a crayfish [4]
Fishermen declare that “Hen Lobsters” protect their young in a similar manner.[5] Jonston,[6] who wrote in the middle of the seventeenth century, says that the little crayfish are often to be seen adhering to the tail of the mother. Roesel’s observations imply the same thing; but he does not describe the exact mode of adherence, and I can find no observations on the subject in the works of later writers.
[4] “Der Monatlich-herausgegeben Insecten Belustigung.” Dritter Theil, p. 336. 1755.
[5] Bell’s “British Crustacea,” p. 249.
[6] “Joannis Jonstoni Historiæ naturalis de Piscibus et Cetis Libri quinque. Tomus IV. ‘De Cammaro seu Astaco fluviatili.’”
It has been seen that the eggs are attached to the swimmerets by a viscid substance, which is, as it were, smeared over them and the hairs with which they are {43} fringed, and is continued by longer or shorter thread-like pedicles into the coat of the same material which invests each egg. It very soon hardens, and then becomes very firm and elastic.
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). Hence, when the chelæ have closed upon anything soft enough to allow of the imbedding of these hooks, it is very difficult, if not impossible, to open them again.
Immediately the young are set free, they must instinctively bury the ends of their forceps in the hardened egg-glue which is smeared over the swimmerets, for they are all found to be holding on in this manner. They exhibit very little movement, and they bear rough shaking or handling without becoming detached; in consequence, I suppose, of the interlocking of the hooked ends of the chelæ imbedded in the egg-glue.