M. J. D'Udekem on the Metamorphoses of the Vorticclle. 5 



its integuments (Opalina or Bursaria) ; 3. the transformation of 

 the Opalina into an Acineta ; 4. the appearance of ciliated em- 

 bryos in the interior of the Acineta; and, 5. the transformation 

 of the ciliated embryos into young Acineta. 



1. The Encystment. 



The encystment, observed first by M. Stein in different species 

 of Vorticellina, and subsequently by several naturalists in many 

 other Infusoria, now appears to exist among all the animals of 

 this class. I shall deal here only with the Vorticellina. I shall 

 first indicate in what species the encystment has been observed; 

 then, how it takes place ; I shall discuss, in the third place, the 

 view which is to be taken of this phenomenon, and what is its 

 probable purpose. 



I have observed the encystment in four species of Vorticella. 

 First, in Vorticella microstoma : this is the example in which it is 

 most easy to see the phenomenon; for in almost all liquids 

 where it is met with, we find cysts at the same time, which, as 

 we shall see further on, does not always happen with the other 

 species. When an infusion containing Vorticella microstoma is 

 concentrated by evaporation in the open air, the cysts become 

 very numerous. The thickness of the cyst differs in different 

 individuals ; sometimes it is thin and fragile, sometimes thick 

 and hard ; sometimes it is covered with prominent points. M. 

 Stein was the first to describe the phenomenon of encystment 

 in Vorticella microstoma. 



I observed the encystment in a species of Vorticella not 

 hitherto described, and which I shall call Vorticella microstyla, 

 on account of the shortness of the style, which never forms a 

 complete turn of a spiral when the animal contracts. I have 

 met with this species only in a single spot in the environs of 

 Brussels. I hope to give a more complete description of it on 

 a future occasion. As the cysts, in this species, very closely 

 resemble those of Vorticella microstoma, they do not require a 

 particular description. 



I have several times met with cysts of Vorticella Convallaria ; 

 but they are more difficult to observe, because, this species being 

 more delicate than those of which I have just spoken, the indi- 

 viduals mostly die without becoming encysted. 



Lastly, I have observed the phenomena of encystment in a 

 fourth species of Vorticella. This species, which I met with 

 upon our coast at Ostend, has not yet been described ; it is ex- 

 tremely remarkable on account of a membranous prolongation 

 surrounding the peristome, which gives it, when expanded, the 

 form of a parasol ; when it is contracted, this membrane becomes 

 plaited and folded up in the interior of the body. 



