Outlines of zoology . means of its cilia it swims actively in the water for somehours, but its sole chance of life depends on its meetinga small amphibious water-snail {Limnmns truncatulus ortiiinuius), into which it bores. In an epidemic amonghorses and cattle in the Hawaiian Islands, the host wasZ. oahuensis; in the Sandwich Islands the host isL. peregra, in Victoria Bulimus tenidstriatus. Thisdiversity of host, also remarkable in the adult, is veryunusual. Within the snail, in the pulmonary chamber,the embryo becomes passive, loses its cilia, increases insize, and becomes a
Outlines of zoology . means of its cilia it swims actively in the water for somehours, but its sole chance of life depends on its meetinga small amphibious water-snail {Limnmns truncatulus ortiiinuius), into which it bores. In an epidemic amonghorses and cattle in the Hawaiian Islands, the host wasZ. oahuensis; in the Sandwich Islands the host isL. peregra, in Victoria Bulimus tenidstriatus. Thisdiversity of host, also remarkable in the adult, is veryunusual. Within the snail, in the pulmonary chamber,the embryo becomes passive, loses its cilia, increases insize, and becomes a sporocyst. The sporocyst is a hollowsac, with a slightly muscular wall and with the beginningsof an excretory system. Sometimes this sporocyst dividestransversely (Fig. 97 (4)). Within the sporocyst a few cells behave like partheno-genetic ova. Each segments into a ball of cells or morula,which is invaginated into a gastrula, and grows into anotherform of larva^the redia. These redise burst out of the LIVER FLUKE, xS7. FiO. 97.—Life history of liver fluke.—After Thomas. I, Developing embryo in. egg-case; 2. free-swimming -ciliated embryo;3. sporocyst; 3«. shell of LzTnneEus^ truncatulus; 4. division of sporo-cyst; 5. sporocyst witli redi_Ee forming within it; 6. redia with morerediee forming within it; 7. tailed cercaria; 8. young fluke. i88 UNSEGMENTED WORMS. sporocyst, and migrate into the liver or some other sporocyst usually forms at a time 5-8 redi^; eachof these forms 8-12 more rediae; and each of these forms14-20 cercarise. In the winter a sporocyst may give riseto cercariae directly. A redia is a cylindrical organismwith a short alimentary canal, excretory canals with flamecells, and a pair of blunt locomotor processes cercaria has a bifurcated gut, two suckers, a locomotortail, and the beginnings of gonads (Fig. 97 (6)). The cercarise emerge from the redise, wriggle out of thesnail, pass into the water, and after swimming for a shorttime,
Size: 1228px × 2034px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
