80 SURVEY OF THE REPRODUCTIVE PROCESS 



secretion which gradually consolidates into a hard shell. 

 In some cases the encystment seems to depend on exposure 

 to cold or drought, and is then probably simply a means of 

 protection from these influences a sort of hybernation 

 for the animal may remain unchanged in the cyst, and, 

 when humidity and warmth are restored, it may burst its 

 envelope and resume its former life. But in other instances 

 it appears to have a physiological import, and to be preli- 

 minary to certain transformations of the animalcule itself. 

 Stein mentions several metamorphosis undergone by the 

 Vorticella in the interior of the cyst, especially its breaking 

 up into a number of minute corpuscules, which, on reaching 

 maturity, are shed by the dehiscence of the shell, and serve 

 as free gemmse for the multiplication of the species. He 

 describes also the conversion of the cyst itself into an 

 Acineta, by the protrusion from its exterior of the charac- 

 teristic knobbed tentacles. The convertibility of these two 

 forms, and many others of Stein's conclusions, are rejected 

 by Lachmann on the ground that sufficient care was not 

 taken in the isolation of the specimens observed. More 

 lately, however, M. d'Udekem has reasserted the derivation 

 of acineta forms from the encysted Vorticella, though he 

 differs from M. Stein in his account of the metamorphosis. 

 He describes the transformation of the Vorticella within 

 the cyst into a simple ciliated Infusorian (Opalina), by its 

 dissolution into granules, the exterior layers of which coa- 

 lesce to form an integument, by a process somewhat resem- 

 bling the formation of the blastodermic membrane of the 

 ovum. The ciliated body after escaping from the cyst, 

 which is ruptured by its growth, is transformed into an 

 Acineta. By careful isolation, and the observation of in- 

 termediate forms, M. d'Udekem has satisfied himself of the 

 reality of this change. Ciliated embryos, formed from the 

 nucleus, have been seen by many observers to be discharged 

 from the Acineta. Stein observed these, though he was 



