M. J. D'Udekem on the Metamorphoses of the Vorticellse. 11 



metamorphosis of Vorticellina into Acinetce is improbable, be- 

 cause it cannot be compared with anything taking place in other 

 animals. I shall answer this in the words of a great physiolo- 

 gist : " One must be very bold to assign limits to nature.'" 



4. Appearance of Ciliated Embryos in the interior of the Acinetse. 



The discovery of the origin of ciliated embryos in the interior 

 of the Acinetce is due to M. Stein. M. Lachmann announces 

 that he has made a similar discovery in a great number of Aci- 

 netce. I also found this embryo in the Acineta of Epistylis 

 plicatilis, and subsequently in all the Acinetce I have met with, 

 among which are many species not yet described. All naturalists 

 are now agreed as to the appearance of the ciliated embryos in 

 the Acinetce, and their formation at the expense of the nucleus ; 

 but one point is still controverted, namely the manner in which 

 the nucleus behaves during the production of the embryo. Ac- 

 cording to M. Stein, the division of the nucleus appears to precede 

 the formation of the embryo ; but M. Cohn regards this division 

 as improbable. It appears that M. Lachmann has studied this 

 question with much care ; but as he only gives the result of his 

 observations on the Infusoria in general, and not especially for 

 the Acinetce, it is impossible to know his opinion upon this 

 point. With regard to myself, notwithstanding all the pains I 

 have taken, I have never been able to see the division of the 

 nucleus of the Acinetce before the production of the embryo, as 

 indicated by M. Stein ; on the contrary, I have always seen the 

 nucleus totally converted into an embryo, and after the expul- 

 sion of the latter, a new nucleus has been formed, which, in its 

 turn, became transformed into a new embryo, and so on. 



5. Transformation of the Ciliated Embryos into young Acinetse. 



M. Stein, after discovering the production of ciliated embryos 

 in the interior of the Acinetce, stated, as a very probable hypo- 

 thesis, that these embryos, once free, become transformed into 

 Vorticellina ; however, he never succeeded in tracing the ulterior 

 development of these embryos ; the latter always escaped him. 

 More fortunate than M. Stein, M. J. Miiller succeeded in tracing 

 these embryos, and saw them become fixed, and transformed into 

 young Acinetce. M. Lachmann arrived at the same result. 



These observations of MM. Miiller and Lachmann were not 

 yet known, as I have already said, in Belgium when I presented 

 to the Academy my work on the development of Epistylis pli- 

 catilis ; in that work I described this curious transformation of 

 the ciliated embryo into a young Acineta, thinking myself the 

 first to observe it. Since then, I have succeeded in detecting 



