The microscope and its revelations . often, in the first instance, so completely buriedwithin this, as only to be discoverable by tearing its portionsasunder; but some of them may commonly be found upon itsexterior; and those contained in one capsule very commonlyexliibit the different stages of development represented inFig. 271, H—K. After a short time, however, it becomesapparent that the most advanced embryoes are begianing toswallow the yolk-segments of the conglomerate mass; andcapsules wiU not unfrequently be met-with, in which embryoesof various sizes, as a, h, c, d, e (Fig. 272, a), a
The microscope and its revelations . often, in the first instance, so completely buriedwithin this, as only to be discoverable by tearing its portionsasunder; but some of them may commonly be found upon itsexterior; and those contained in one capsule very commonlyexliibit the different stages of development represented inFig. 271, H—K. After a short time, however, it becomesapparent that the most advanced embryoes are begianing toswallow the yolk-segments of the conglomerate mass; andcapsules wiU not unfrequently be met-with, in which embryoesof various sizes, as a, h, c, d, e (Fig. 272, a), are projectingfrom its surface, their difference of size not being accompaniedby advance in development, but merely depending upon theamount of this supplemental yolk which the individuals haverespectively gulped-down. For during the time in which they DEYELOPMEKT OF GASTEEOPODS :—PURPUKA. 613 are engaged in appropriating this additional supply of nutri-ment, althougli they increase in size, yet they scarcely exhibit Fig. 272. c. /-R^U Later stages of embryonic development of Purpura lapillus:—A, conglomerate mass of vitelline segments, to which were attachedthe embryoes, a, b, c, d, e.—b, full-sized embryo, in more advancedstage of development. any other change; so that the large embryo, Fig. 272, e, isnot apparently more advanced as regards the formation of itsorgans, than the small embryo, Eig. 271, k. So soon as thisoperation has been completed, however, and the embryo hasattained its full bulk, the evolution of its organs takes-placevery rapidly; the ciliated lobes are much more highly deve-loped, being extended in a long sinuous margin, so as almostto remind the observer of the vrheels of Rotifera (§ 277),and being furnished with very long cilia (Fig. 272, b); theauditory vesicles, the tentacula, the eyes, and the foot, succes-sively make their appearance; a curious rhythmically-con-tractile vesicle is seen, just beneath the edge of the sheUin the region of the ne
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