. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 324 PLATYHELMINTnES. into the branchial cavity of the tadpole, lose their cilia, and are transformed into young Pnhjstomea by the formation of the two median hooks and of the three pairs of suckers upon the posterior disc. The young Polystomum, eight weeks after the migration into the branchial cavity, at the time when the latter begins to abort, passes through the stomach and intestine into the bladder, and there. Fig. 260.—Young Diplozoon (after E. Zeller). a. Two young JDiporpa beginning to attac
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 324 PLATYHELMINTnES. into the branchial cavity of the tadpole, lose their cilia, and are transformed into young Pnhjstomea by the formation of the two median hooks and of the three pairs of suckers upon the posterior disc. The young Polystomum, eight weeks after the migration into the branchial cavity, at the time when the latter begins to abort, passes through the stomach and intestine into the bladder, and there. Fig. 260.—Young Diplozoon (after E. Zeller). a. Two young JDiporpa beginning to attach themselves together. 6, After both individuals have attached themselves. O, mouth; H, fixing apparatus; Z, papillje; G, sucker. only becomes sexually mature after three and more years. In some exceptional cases, and always when the larva has passed on to the gills of a very young tadpole, it becomes sexually mature in the branchial cavity of the latter. The forms then remain very small, are without the copulatory canals and uterus, and die after the production of a single egg, without ever getting to the bladder. Fam. Polystomidae. With seve- ral posterior suckers, which are usually paired and arranged in two lateral rows, and are rein- forced by an armature of hooks. The genital openings are fre- FiG. (a) and larva (6) of Diplozoon (after quently surrounded by hooks. E. Zeller). Many species have a length of only a few lines. Polystomum Zed., with four eyes ; with no lateral suckers at the anterior end, but with oral sucker; with six suckers, two large median hooks and sixteen small hooks at the posterior end. P. inteijerrlmnm Eud., in the bladder of Rana tcmjwrarla. P. ocellatuvi in the pharyngeal cavity of Emys. In the formation of the testis and the absence of the uterus it resembles the adult form of P. integerrimum from the branchial cavity of the tadpole. Octohothrium lanceolatiim Duj. OncJiocotyle appendiculata', on the gills of Elasmobranchs. Diploz
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
