. Elementary text-book of zoology. Zoology. 320 tailed Cercarice, or to another generation of ftporocysts or Redice,* which then produce the Cercaria-. The CercaricK are nothing else than Distoniuni lai-vte, which eventually reach (often only after two migrations, an active and a passive one) the final host, where they become sexually mature. They are furnished with an exceedingly motile caudal appendage, frequently with a buccal spine, and occasionally with eyes, and they present in the rest of their organization great resemblances to the adult Distomum, excepting that the g
. Elementary text-book of zoology. Zoology. 320 tailed Cercarice, or to another generation of ftporocysts or Redice,* which then produce the Cercaria-. The CercaricK are nothing else than Distoniuni lai-vte, which eventually reach (often only after two migrations, an active and a passive one) the final host, where they become sexually mature. They are furnished with an exceedingly motile caudal appendage, frequently with a buccal spine, and occasionally with eyes, and they present in the rest of their organization great resemblances to the adult Distomum, excepting that the generative organs are not developed. In this form they leave independently the body of the Redia or Sjmrocyst and of the host of the latter, and move about in the water, partly creeping and partly swimming. Here they soon find a new host (Snail, Worm, Insect larva, Crustacean, Fish, Batrachian), into which they penetrate, aided by the powerful vibrations of their tail ; they then lose the latter and encyst. The Cercarice from the interior of the snail thus become distributed amongst a number of hosts, and each of them gives rise to an encyste young Distonmm without generative organs. This young Distomum mi- grates passively with the flesh of its host into the stomach of another animal, and thence, freed from its cyst, into the organ (intestine, bladder etc-)- in which it becomes sexually mature. There are, then, as a rule, three different hosts in the organs of which bold). P, Pigment spots; E, redia, in tho interior of the embryo, the different developmental stages (Redia or Sporocyst, encysted form, sexually mature animal) of the Distomum bury themselves. The transitions from one host to another are effected partly by inde- pendent migration (embryos, Cercarise), partly by passive migration (encysted young Distomum). Modifications of the ordinary course of development may, however, take place ; these may be either complications or simplifications. The embryo at hatching may co
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
