Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 POLTCH^ilTA. 377 dorsal and ventral trunks may perform the function of hearts, as is also frequently the case in the Ol'ujochceta. Finally the vascular system is in many cases considerably reduced, and, according to Clapar^de, is entirely wanting in Glycera and Capitella, in which the blood is represented by the perivisceral fluid. The generative organs, unlike those of the hermaphrodite Oligo- chcBta, are usually placed in different in
Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 POLTCH^ilTA. 377 dorsal and ventral trunks may perform the function of hearts, as is also frequently the case in the Ol'ujochceta. Finally the vascular system is in many cases considerably reduced, and, according to Clapar^de, is entirely wanting in Glycera and Capitella, in which the blood is represented by the perivisceral fluid. The generative organs, unlike those of the hermaphrodite Oligo- chcBta, are usually placed in different individuals; and the males and females are sometimes of very different forms. A number of herma- phrodite Polijchceta are, however, known ; such principally belong to genera of the Serpulidce, , Spirorhis, Protula. The development, unlike that of the Oligochceta, is invariably con- nected with a metamorphosis. Segmentation is, as in the Hirudi- nea, usually un- equal, and even the first two seg- mentation spheres are of unequal size. The smaller (animal) half, which segments more quickly, gives rise to smaller segments, which grow round and envelope the larger segments proceeding from the segmentation of the larger half. In the subsequent development a primitive streak makes its appearance in all embryos of PolycJiceta, sometimes, how- ever, not until the embryo has begun to lead a free life as larva. The ganglia become differentiated later into the ventral chain. In the free-swimming larvae the cilia are rarely distributed over the whole surface of the body {Atrocha*'). They are usually confined to special rows (ciliated rings); sometimes, as in Loven's larva, there is one row placed in front of the mouth at some distance from the * Compare E. Clapar^de and E. Metschnikoff, ' Beitrag* znr Entwickelungs- geschichte der Chretopoden,' Zeitschr. fiir wiss. Zool., Tom. XIX., 1869. Fig. 306.—Larvae of Tolychata (after Busch). a, Larva of 'Nereii F, tentacle; Oc, eyes; FrTF, p
Size: 1445px × 1384px
Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
