Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 GANOIDEI. 165 gills, on the other hand, lie, as in the Teleosteans, freely in a branchial cavity beneath a branchial operculum, to which a large gill containing venous blood is often attached. This respiratory accessory gill (opercular gill) is wanting in Amia and Spatula/ria, and must be distinguished from the pseudobranch of the spiracle, which may be present together with it. All the Ganoids possess a swimming bladder with a ductus pneu- maticus and two peritoneal canals (abdominal po
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 GANOIDEI. 165 gills, on the other hand, lie, as in the Teleosteans, freely in a branchial cavity beneath a branchial operculum, to which a large gill containing venous blood is often attached. This respiratory accessory gill (opercular gill) is wanting in Amia and Spatula/ria, and must be distinguished from the pseudobranch of the spiracle, which may be present together with it. All the Ganoids possess a swimming bladder with a ductus pneu- maticus and two peritoneal canals (abdominal pores), which open at the sides of the anus (as in Ghimcera and Playiostomi}. The optic nerves do not simply cross over one another, but form a chiasma with partial exchange of the fibres. The generative organs present many noteworthy peculiarities. There are two ovaries and the ripe eggs escape into the abdominal cavity. Thence they pass into an oviduct [Miilleriaii duct] which begins with a funnel-shaped opening into the body cavity and opens behind into the urinary duct or into the corresponding cornu of the urinary bladder (Spatularia, Lepi. FIG. 608.—Acipenser rufheims (after Heckel and Kner). dosteiis), or unites with the oviduct of the opposite side and opens behind the anus by a single genital pore into which the short urethra also opens. (Hyrtl.) In the two first cases a urogenital canal leads from the bladder to a urogenital pore placed behind the anus. In the male it is remarkable that the same abdominal funnels [Miillerian ducts] also function as seminal ducts. [It has been shown by Balfour and Parker (Structure and Development of Lepidosteus, Phil. Trans., 1882), that in Lepidosteus at any rate the testis is connected with the Wolffian body by a testicular network.] Tribe 1. Chondrostei. Cartilaginous Ganoids with persistent notochord. Branchiostegal rays scanty or absent. Caudal fin heterocercal, with fulcra. Cranium cartilaginous, covered by dermal bones. The
Size: 2805px × 713px
Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
