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 ; 3 T , nucleus ; the mouth apparatus in each por- 

 tion is formed afresh, oe, gullet. J, Fission is completed, 

 the smaller product is set free after the formation of a 

 posterior ring- of cilia ; , adoral zone of cilia, c, Vorti- 

 cella in process of bud-like conjugation ; A', the bud-like 

 individuals attached. 



