The microscope and its revelations . embryo of Lymnseus, save that its swimming movements areless active, in consequence of the inferior development of theciliated lobes; and the currents produced by these seem tohave reference chiefly to the provision of supplies of food, andof aerated water for respiration. The disappearance of theciha has been observed by ^Ir. Hogg to be coincident withthe development of the teeth to a degree sufiicient to enablethe young water-snail to crop its vegetable food; and he hasfuither ascertained, that if the growing animal be kept infresh water aloiie for some t
The microscope and its revelations . embryo of Lymnseus, save that its swimming movements areless active, in consequence of the inferior development of theciliated lobes; and the currents produced by these seem tohave reference chiefly to the provision of supplies of food, andof aerated water for respiration. The disappearance of theciha has been observed by ^Ir. Hogg to be coincident withthe development of the teeth to a degree sufiicient to enablethe young water-snail to crop its vegetable food; and he hasfuither ascertained, that if the growing animal be kept infresh water aloiie for some time, without vegetable matter ofany kind, the gastric teeth are very imperfectly developed, andthe ciHa are still retained.* 851. A very curious modification of the ordinary plan ofdevelopment, is presented in the Purpura lapilhis; and it isprobable that something of the same kind exists also inBuccinum, as also in other Gasteropods of the same extensiveorder {Fedinibranchiata).—Each of the capsules akeady de-scribed (§ 349) con-. #>^ tains from 500 to 600 Fig. egg-like bodies (, a), imbedded in aviscid gelatinous sub-stance ; but only from12 to 30 embryoesusually attain com-plete development;and it is obvious fromthe large comparativesize which these attain(Pig. 272, b), thateach of them mustinclude an amount ofsubstance equal tothat of a great num-ber of the bodies ori-ginally found withinthe capsule. The ex-planation of this fact(long since noticed by Dr. J. E. Gray in regard to Buc-cinum) seems to be as follows:—Of those 500 or 600 egg-
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