Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 202 PEOTOZOA. preservation of the Infusoria from desiccation. The animal retracts its cilia, contracts its body to a globular mass, and then secretes a transparent cyst, which hardens and protects the animal, thus en- abling it to survive in damp air. In the water, the contents of the cyst divide into a number of parts, which attain freedom by the bursting of the cyst, each one becoming a young animal. Moreover, many I
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 202 PEOTOZOA. preservation of the Infusoria from desiccation. The animal retracts its cilia, contracts its body to a globular mass, and then secretes a transparent cyst, which hardens and protects the animal, thus en- abling it to survive in damp air. In the water, the contents of the cyst divide into a number of parts, which attain freedom by the bursting of the cyst, each one becoming a young animal. Moreover, many Infusoria (Acineta*) produce with participation of the nucleus a number of buds asexually, which separate them- selves from the walls of the parent body (fig. 142). The broods of Sphserophrya make their way into the interior of other Infusoria, as Paramaecium and Stylonychia, nourish ihemselves at the cost of the enlarged nu- cleus, and form em- bryos by fission. These embryos swarm out, and were for a long time taken by Stein for the embryo broods of Stylonychia (tig. 144, J). The process of con- jugation observed by Leeuwenhoek and O. Fr. Miiller is very general, and is con- nected with changes of the nucleus and nucleolus. These changes, which gave rise to the erroneous interpretation of the two structures as ovary and testis, are in reality simply preparatory to a process of regeneration of the nucleus by parts of the paranu- cleus, a process comparable to the phenomena of the fertilization of the ovum in sexual reproduction. The conjugation of two Infusoria occurs in very different ways, and leads to a moi-e or less complete fusion, which, after regeneration of the nucleus, is followed by an increase in the frequency of fission. Paramcecium, Stentor, Spirostoma, dining conjugation, become con- II FIG. 143.— Vorticella micrcstoma (after Stein), a, In process of fission ; 3T, nucleus; the mouth apparatus in each por- tion is formed afresh, oe, gullet. J, Fission is compl
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