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



previously contained. Once free, the latter swims about, and seeks 

 a suitable place on which to fix itself. Having found this, it pro- 

 ceeds to undergo a new metamorphosis, which may produce two 

 different forms. Sometimes the Opalina, which is spherical or 

 more or less oval, becomes fixed by one of its extremities, whence 

 arises a style, which grows rapidly; at the other extremity 

 appear four bundles of retractile tentacles. 



" In the second case, the Opalina does not become fixed by 

 one of its extremities, but seems to become flattened out upon 

 the foreign body ; it remains sessile, and a more or less con- 

 siderable number of bundles of tentacles appear on its circum- 

 ference. In the two preceding cases, the vibratile cilia covering 

 the integument of the Opalina vanish from the moment when it 

 becomes fixed. 



"The two forms which I have just described are Acinetce. 

 The first is identical with that represented by M. Stein, pi. I. 

 fig. I. D. of his work; the second is an Acineta not hitherto 

 described. The metamorphoses of Epistylis plicatilis stop here. 

 The Acinetce grow, and become more and more developed. In 

 their interior is found a nucleus, which increases in size, and 

 makes its way towards the internal surface of the integuments. 

 By the contractions of the animal, the latter become ruptured, 

 and the nucleus is set free. This nucleus, which is really a bud, 

 of discoidal form, moves with extreme activity by the aid of long 

 vibratile cilia which decorate its surface. The Acinetce give 

 birth, successively, to several ciliated buds, and terminate their 

 existence without undergoing any further metamorphosis. 



" The ciliated buds, after their emission from the Acinetce, 

 become metamorphosed into young Acinetce] they affix them- 

 selves to a foreign body, either remaining sessile or producing a 

 style ; their vibratile cilia disappear, and are replaced by four 

 bundles of tentacles. 



"The new nuclei reproduce new ciliated buds in their in- 

 terior.^' 



From this it will be seen that I thought myself the first dis- 

 coverer of the transformation of the ciliated embryos into young 

 Acinetce ; I hasten to restore the property in this discovery to its 

 rightful owner, the illustrious physiologist, J. Miiller. 



Now that I have given the history of the question, I shall 

 attempt, from the materials furnished by the observations of my 

 predecessors and by my own, to show that what I have described 

 of Epistylis plicatilis will apply to many species of Vorticellina, 

 and perhaps to all. 



I shall examine, then, 1 . the encystment ; 2. the transforma- 

 tion of the Vorticellian in the interior of the sac into an Infu- 

 sorium with its whole surface ciliated, and without any orifice in 



