M. J. D'Udekem on the Metamorphoses of the Vorticellse. 9 



the existence of a metamorphosis. But, before commencing this 

 discussion, I will give the description of this new transforma- 

 tion. 



I have indicated in the preceding paragraph that certain Vor- 

 ticellina become transformed, in the interior of a cyst, into a 

 spherical Infusorium having an integument closed at all points, 

 and entirely covered with vibratile cilia. This new Infusorium 

 performs, within its envelope, a continual rotation. In another 

 paper, I have compared this rotation to that performed by the 

 embryos of Gasteropod MoUusca within the egg. 



While the metamorphosed Vorticellian revolves, it undergoes 

 development, increases in size, and its whole surface becomes co- 

 vered with folds j finally, a moment arrives when the cyst, yield- 

 ing to the pressure exerted in its interior, bursts ; the ciliated 

 Infusorium becomes free, and swims with a rotating movement. 



To discover how this Infusorium becomes transformed into an 

 Acineta requires attentive observation, in order to avoid all the 

 chances of error which may present themselves, and which are 

 numerous. 



I believe myself authorized in supposing the existence of this 

 metamorphosis, because I have observed Infusoria which pre- 

 sented, on the one hand, all the characters of Acineta, and, on 

 the other, the characters of the Infusorium produced by the 

 transformation of the Vorticellina. 



Three times I have observed individuals of Acineta mystacina 

 already provided with tentacles, and which had the spherical 

 form and the body covered with vibratile cilia. I have doubtless 

 seized in those cases the moment of the metamorphosis of the 

 ciliated Infusorium [Opalina) into an Acineta. It may be ob- 

 jected that the cilia with which these Acineta were covered be- 

 longed to the embryonary state ; the answer to this objection is 

 easy : the cilia of the embryos are arranged in a totally different 

 manner, and occur only upon Acinetce of very small size ; they 

 fall off very early, before the appearance of the tentacles. 



I shall now discuss the objections of M. Lachmann against 

 the theory of M. Stein, so far as they might be applied to my 

 opinion. M. Lachmann thinks that the forms indicated by M. 

 Stein as degrees of transition between the Vorticellina and the 

 Acinetce, are really only different species of Infusoria, which have 

 no other relation beyond a more or less considerable resemblance. 

 This objection is indeed applicable to the observations of M. Stein. 

 That author has not taken sufficient pains to show the inter- 

 connexion of the different transitory forms. For my own part, 

 I think I am entirely out of reach of this objection, and what is 

 said above sufficiently proves it ; thus I have demonstrated how 

 certain Vorticellina become transformed into ciliated Infusoria 



