Elementary text-book of zoology Volume 1
Carl Friedrich Wilhelm Claus
Paperback
(RareBooksClub.com, March 6, 2012)
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1884 Excerpt: ...former is frequently removed from the ventral surface of the anterior end of the body to the middle or, indeed, even to the posterior region. According to Metschnikoff and Ulianin, a stomach may in some cases be absent (Convolutu, Schizoprora), and be replaced, as in Infusoria, by a soft internal parenchyma. The mouth leads into a muscular pharynx, which can usually be protruded after the manner of a proboscis. The alimentary canal, of which the internal wall is frequently ciliated, is either forked and then simple or branched (Deiulroaela), or rod-shaped (Ehabdocurii). An anus is never present. A peculiar tube capable of being evaginated as a proboscis, and without connection with the pharynx is sometimes also present (Prostomum). The excretory (water-vascular) system consists of two transparent lateral trunks and innumerable side branches, which begin with closed ciliated funnels, and are furnished with vibratile cilia, which Fig. 248,--Mierottomum lineare, after Graff. O, Chain produced by fission; O, mouth openings. project here and there freely into the vessels. As a rule, several openings occur on the main trunk of this excretory apparatus. Reproduction may take place asexually by transverse fission, e.g., Derostomea (Catenrda) and Microstomia (fig. 248). With the exception 'of the Microstomia, the Turbdlaria are hermaphrodite; but steps intermediate between the hermaphrodite and the dicecious condition seem by no means to be wanting, for, according to Metschnikoff", in Prostomum lineare the male generative organs are sometimes developed, while the female's remain rudimentary; and sometimes, on the other hand, the reverse holds. In Acmostomum diwcum also the sexes are separate. In the hermaphrodite forms the male sexual organs consist of testes, ...