The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . with a tadpole it attaches itselfat once and undergoes further development. If unsuccessful itdies. In the former case the larva creeps along the tadpole untilit reaches the branchial opening into which it darts, fixes its sucker,and then throws off its cilia. Its further development takes placepartly in the branchial chamber and partly in the bladder, whichIt reaches by travelling the whole length of the alimentary the former position the suckers are developed and growth pro-ceeds for 8
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . with a tadpole it attaches itselfat once and undergoes further development. If unsuccessful itdies. In the former case the larva creeps along the tadpole untilit reaches the branchial opening into which it darts, fixes its sucker,and then throws off its cilia. Its further development takes placepartly in the branchial chamber and partly in the bladder, whichIt reaches by travelling the whole length of the alimentary the former position the suckers are developed and growth pro-ceeds for 8 to 10 weeks until the metamorphosis of its host. In thebladder it remains for three years before attaining maturity. Some-times the PolysloinumA^rv^. attaches itself to a young tadpole,and in that case grows so rapidly as to become mature in five Polystomnm deposit their eggs in the branchial chamber anddie at the metamorphosis of their host. They differ structurally from the normal form in being capable of self-fertilization only,*and in the shape and details of their spermatozoa. Fig. 5. A, Diplozoon paradoxum; two united specimens. B, Polyslomiim inlegerrimum, (Xabout loo; after ZeUer.) C, Microcotyle mormyri. D, E, Two views of the chitinous framework of a sucker of Axine helones; highly magnified (after Lorcnz). F, Aspidogasler conchicola. (Xabout 25; after Aubert.) G, Gyrodactylus clegans. (Xabout 80; after Wagener.) The life-history of Diplozoon (fig. 5) is remarkable in that twolarvae (the so-called Dtporpac) unite and fuse permanentlyinto an X-shaped organism. Unless this occurs, the develop-ment of the larvae is soon ciliated stage is only capableof free life for five or six hours, andif at the end of that time it has notencountered and attached itself to aminnow, it dies. If successful, the lar\athrows off its cilia and develops a dorsalpapilla, a median ventral sucker and anadditional pair of lateral suckers. Thenthe Diporpa stage is attain
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
