Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 28 OBGANIZATIOX AXD DEVELOPMENT OF ANIMALS LST GENLEAL. which are placed one behind the other, and more or less completely resemble each other in structure (Annelids, fig. 15). The successive segments may in structure and function appear completely equiva- lent, and represent, like the antimeres of the Radiata, individuals of a lower order, which on the severance of their mutual connec- tion can acquire independence and remain alive for a shorter or lon
Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 28 OBGANIZATIOX AXD DEVELOPMENT OF ANIMALS LST GENLEAL. which are placed one behind the other, and more or less completely resemble each other in structure (Annelids, fig. 15). The successive segments may in structure and function appear completely equiva- lent, and represent, like the antimeres of the Radiata, individuals of a lower order, which on the severance of their mutual connec- tion can acquire independence and remain alive for a shorter or longer period (proyloltis of Cestodes). In animals of higher organization the segments are much more intimately connected, and are mutually dependent, but they lose at the same time their complete homonorny. In the same degree as the metarneres acquire an unlike structure, and corresponding to this a varying importance in the life of the organ- ism, they lose their individual independence, and sink more and more to the value of organs. The metameres in the polymorphous colonies are quite analogous to the segments of the individual. In them there follow, one behind the other, similar groups of different individuals, each of which fulfils singly the conditions necessary for existence, and there- fore can continue to live as a colony of a lower order when separated from the stock (Eudoxia, Diphyes, fig. 16). The order also holds for organs. which are reducible to a single cell, or to an aggregation of equivalent cells (simple organs), and others in the formation of which various cells and tissues (compound organs) partici- pate, and which frequently, in their turn, may be divided into parts different in structure and function. The compound organs of higher order are composed of different parts which function as organs of a lower order. These, again, are composed of various kinds of cell sand cell derivator, which are organs of a still lower order. Finally, in the last analysis, we co
Size: 878px × 2277px
Photo credit: © Bookend / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
