6 M. J. D'Udekem on the Metamorphoses of the Vorticellse. 



M. Stein has observed the encystment of Vorticella nehulifera. 

 In the genus Carchesium, I have observed the cysts of three 

 species — those of Carchesium polypinum, of Carchesium ramo- 

 sissimum, and of Carchesium pygmceum ; there is scarcely any 

 difference between them, and they entirely resemble the cysts of 

 the Vorticella. 



In the genus Epistylis I have only been able to observe the 

 encystment in two species — Epistylis plicatilis, and an Epistylis 

 which I think new, and which I have often met with liviug 

 parasitically upon the posterior extremity of Tubifex and Nais. 

 M. Stein also has observed the encystment of Epistylis plicatilis. 

 I have sought in vain for the cysts of Epistylis grandis and E. 

 fiavicans, two species very common in our environs ; I attribute 

 this to the difficulty of preserving these animals alive in vessels 

 in the study. 



In the genus Opercularia, my observations have been made 

 on Opercularia nutans, O. Lichtensteinii (Stein), and O. micro- 

 stoma. I have seen the encystment only in the first of these 

 three species ; the two others being far more rare, it is not sur- 

 prising that this phsenomenon should have escaped me. 



Finally, M. Stein has observed and described the encystment 

 of Vaginicola crystallina ; I have made a similar observation. 



Summing up all these observations, I shall conclude that spe- 

 cies susceptible of encystment are met with in all the genera of 

 the family of Vorticellina, and that it is very probable that this 

 phsenomenon presents itself in all, when favourable circumstances 

 tend to induce it. 



The Vorticellina may become encysted at all periods of their 

 existence ; they are encysted either while remaining attached to 

 the style or after they have abandoned it, subsequently to the 

 appearance of a basilar crown of cilia. Lastly, while the Vorti- 

 cellina are reproduced by fission, they may still become encysted ; 

 and I have observed among them all the intermediate conditions 

 between the commencement of the division and its completion, 

 simultaneously with the appearance of cysts. 



The encystment takes place in the same manner in all the 

 Vorticellina in which I have observed it. The individual which 

 is about to present this phsenomenon contracts slightly, and 

 closes its peristome ; around it appears a cloud, formed by a 

 viscid liquid, which is probably the result of a cutaneous secre- 

 tion. In this liquid are formed granules, which, augmenting 

 more and more in number and adhering together, finally form 

 a membrane, which becomes hard and resisting, although soft 

 and flexible when first produced. The cyst thus formed does 

 not change its state, or augment in thickness by the deposition 

 of new granules in its interior. When a cyst encloses two indi- 



