Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 103 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. For a long time the behaviour of the germinal vesicle at the commencement of segmentation and its relation to the nuclei of the first formed segments were obscure, and the knowledge of the changes and fate of the spermatozoa which enter the ovum in the process of fertilization was, in like manner, in a very unsatisfactory state. Of late years, numerous investigations, especially those of Biitschli, 0. Hertwig, Fol, etc., have thrown
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 103 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. For a long time the behaviour of the germinal vesicle at the commencement of segmentation and its relation to the nuclei of the first formed segments were obscure, and the knowledge of the changes and fate of the spermatozoa which enter the ovum in the process of fertilization was, in like manner, in a very unsatisfactory state. Of late years, numerous investigations, especially those of Biitschli, 0. Hertwig, Fol, etc., have thrown some light on these hitherto completely obscure processes. It was supposed that in a ripe ovum preparing itself for segmentation the germinal vesicle disappeared, JE* FIG. 102, a, b.—Parts of the ovum of Asterias glacialis with spermatozoa, embedded in the mucilaginous coat (after H. Fol.) c, upper part of the ovum of Petromyzon (after Calberla). Am, micropyle ; Sp, spermatozoa; Jm, path of the speiinatozoon; Ek, female pronucleus; Eh, membrane of ovum; Ehz, prominences of the same. and a new nucleus was formed quite independently of it; and that the persistence and the participation of the germinal vesicle in the for- mation of the nuclei of the first segmentation spheres were exceptional (Siphonophora, Entoconcha, etc.) Thorough investigations carried out on the eggs of numerous-animals have, however, shown that as a matter of fact the germinal vesicle of the ripe ovum only experi- ences changes in which the greater part of it, together with some of
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