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



{Opalina), and how these Opalirus become covered with tentacles 

 and metamorphosed into Acinetce, 



The second objection of M. Lachmann against M. Stein rests 

 on the opinion that the simultaneous appearance of Acinetce and 

 Vorticellina in the same infusion cannot be regarded as a sign 

 of relationship between these two species. I quite agree with 

 M. Lachmann upon this point; however, I believe that the 

 simultaneous appearance of two Infusoria always and every- 

 where in the same infusion affords great probability of the real 

 existence of the metamorphosis of one species into the other. 

 Numerous observations have led me to the certainty that one 

 may almost affirm, a priori, that where a species of Vorticellina 

 is observed, we shall find a species of Acineta^ and vice versa. 



Not only have I found most of the Acinetce described by M. 

 Stein as accompanying certain Vorticellina, but, further, when I 

 have met with a new Vorticellian, I have at the same time found 

 a new species of Acineta. 



A third objection of M. Lachmann must be taken into serious 

 consideration. According to him, the alternation of the appear- 

 ance of the Vorticellina and the Acinetce in the same infusion 

 does not in any way indicate that one species arises out of the 

 transformation of the other. Indeed this alternation occurs with 

 a very great number of Infusoria ; and, as M. Lachmann has 

 rightly said, this is what led MM. Pineau, Gros, and Laurent 

 to suppose that most of the species of Infusoria are only stages 

 of development of one and the same species. M. Lachmann 

 adds — " An alternation of the appearance of certain Infusoria 

 may really give a demonstration of the relationships which exist 

 between them, if one makes certain, by complete isolation in a 

 very circumscribed space, that only individuals of one species 

 exist there.^' 



M. Stein has, it is true, neglected this experiment; for my 

 own part, I have repeated it several times, and, after numerous 

 efforts, I have discovered Acineta in the liquid in which I had 

 isolated specimens of Epistylis plicatilis. I must confess, how- 

 ever, that I do not attach the same importance to these experi- 

 ments that M. Lachmann attributes to them ; the causes of error 

 are too numerous, — above all, on account of the great difficulty 

 of completely isolating a species of Infusorium. 



The other objections of M. Lachmann are addressed to the 

 second portion of M. Stein's theory, that is to say, to the trans- 

 formation of the embryos of Acinetce into Vorticellina. It is 

 unnecessary for me to discuss this here ; that question is now 

 cleared up, as I have already said, in the historical summary 

 which stands at the head of this paper. 



M. Lachmann terminates his objections by saying that the 



