. Animal biology. Zoology; Biology. 258 METAZOAN PHYLA cells are transferred by the first two pairs of swimmerets of the male from the opening of the vasa deferentia to the seminal receptacles of the female. The seminal receptacles are cavities inclosed in folds of the cuticula between the fourth and fifth pairs of walking legs. There the sperm cells remain until the eggs are matured. At this time the latter are passed out of the oviducts, which open at the bases of the third pair of legs, and backward in a groove between the bases of the legs of the two sides of the body, receiving sperm cell
. Animal biology. Zoology; Biology. 258 METAZOAN PHYLA cells are transferred by the first two pairs of swimmerets of the male from the opening of the vasa deferentia to the seminal receptacles of the female. The seminal receptacles are cavities inclosed in folds of the cuticula between the fourth and fifth pairs of walking legs. There the sperm cells remain until the eggs are matured. At this time the latter are passed out of the oviducts, which open at the bases of the third pair of legs, and backward in a groove between the bases of the legs of the two sides of the body, receiving sperm cells and being fertilized on the way. The eggs finally become attached to the swimmerets by a gluelike secretion, masses of them appearing like so many bunches of grapes (Fig. 158). They remain attached during development, their aeration being assisted by movements of the Fig. 158.—A female crayfish with eggs attached to her swimmerets. (From Andrews, in Am. Natur., vol. 38.) Cleavage is superficial and the embryo develops from a thickening of the blastoderm on one side. Limb buds appear, which correspond to the different appendages; metameres are formed; and the embryo gradu- ally assumes the characteristics of the adult. Hatching takes place in from five to eight weeks, but the larvae remain clinging to the swimmerets of the mother for about four weeks longer. During this time they grow, shedding the exoskeleton at intervals but undergoing no metamorphosis. The process of shedding, which is an adjustment to permit growth, is known as molting, or ecdysis. This occurs seven or more times during the summer. It is said that the life of the crayfish covers a span of from three to four years. They reproduce annually after the second year. 297. Regeneration and Autotomy.—Crayfishes have the power of restoring lost appendages, and under normal conditions the same sort of appendage is restored as that which was lost. Under experimental or abnormal conditions, however, an
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