464 Dr. R. Greef on the Structure and 



in size from the latter. Owing to the continual strong contrac- 

 tion of the body, however, it is difficult to ascertain how the 

 alimentary tube behaves in the act of fission ; but at any rate 

 each half receives one or the other section of it, replacing the 

 •deficient portion by new formation. In the Vorticellas which 

 do not form stocks, as is well known, only one of the fissional 

 scions remains upon the parent stalk, or in the parent cell ; 

 tlie other separates completely after it has formed what is 

 called the posterior circlet of cilia, which commences by a 

 transverse annular furrow making its appearance at the poste- 

 rior end of the body where the conical base passes into the 

 bellied bell-shaped portion, and afterwards becoming a cushion- 

 like ridge. Upon this ridge the circlet of cilia is developed 

 (PI. XII. fig. 3, h). 



Besides bifission, a second kind of asexual propagation has 

 been described among the Vorticellas, and, indeed, long ago, 

 namely by Spallanzani and others in the last century. This 

 is a formation of buds, by which a comparatively small portion 

 of the body of the parent is pushed out in the form of a bud 

 at the side walls, and gradually constricted off as a new scion. 

 Stein has the merit of having furnished the very interesting 

 proof that these bud-like structures observed on the bodies of 

 Vorticellaj are in reality not buds (that is to say, products of 

 their bearer) ^ but small fissional scions produced by the several 

 times repeated longitudinal fission of other individuals, which 

 swim from without to the larger individuals, and attach them- 

 selves to their lateral walls, becoming united with them, and 

 thus completing an " act of conjugation." Stein has traced 

 this extremely remarkable process by a series of careful in- 

 vestigations, and named it gemmiform conjugation. 



It would carry us beyond the purpose of this little memoir 

 if we were to follow, even in abstract. Stein's series of obser- 

 vations on gemmiform conjugation and the reproduction of the 

 Vorticellse in general, which have been treated by him with 

 the most minute detail, but unfortunately are still entirely un- 

 illustrated by figures, which would facilitate our comprehension 

 of them. I will therefore for the present confine myself to 

 presenting briefly my own observations in comparison with 

 Stein's, in the hope of being able, hereafter, in continuation of 

 this, to offer something further, as, with regard to both the 

 Vorticellte and other Infusoria, there is still much obscurity 

 that requires clearing up ; or at least the clearness which Stein 

 supposes to have been attained is far from existing. It is 

 only by the most many-sided and unprejudiced observations 

 both of the Infusoria and of the other sections of the Protozoa, 

 without at once drawing from every detail far-reaching general 



