Natural History of the Vorticellee. 465 



conclusions (which often rather hinder than forward knowledge) , 

 that it may be possible to separate those things which really 

 belong to the cycle of reproduction from other phenomena, 

 and to group them together so as in time to obtain a fixed 

 point of view. 



In the first place I have been able in many cases to con- 

 firm the important observation of Stein that the gemmiform 

 appendages of the Vorticellas are not products of their sup- 

 porters, or true buds of them, but smaller individuals pene- 

 trating from without and uniting with them, and that, conse- 

 quently, throughout the Vorticcllte, no reproduction by gemma- 

 tion or sprouting seems to occur. 



The first observations relating to this point were made 

 several years ago during a sojourn in the North Sea (at 

 Ostend) on a marine form which is abundant there, usually 

 adherent to Alg«. In this Vorticellan I was at once struck 

 by the comparatively very frequent occurrence of bud-like 

 structures on the lateral walls of the individual animals, these 

 otherwise in general only rarely coming imder observation. 

 In the above-mentioned Vorticella, which differs in its whole 

 habit from the marine Vorticella patellina of Ehrenberg, found 

 by him near Wismar, in the North Sea, and therefore may 

 probably be a distinct species, I was able to trace the whole 

 process of the so-called gemmiform conjugation, step by step, 

 as I have represented it in PL XIII. figs. 1-7. In fig. 1 a 

 small individual furnished with the posterior circlet of cilia 

 has swum up to a larger one. The ciliary organ is retracted, 

 and the conical base directed perpendicularly towards the 

 lateral walls. ■ Thus we see the smaller individual creep 

 about upon the surface of the larger one by means of the 

 cilia, which are constantly in undulating movement, some- 

 times skipping up and down, sometimes creeping round it, 

 and apparently feeling and seeking everywhere. In spite of 

 the frequent jerkings back of the larger individual, which 

 seem as though it was trying to escape from the irritations 

 produced by the intruder, the latter obstinately persists in 

 holding the position which it has once selected. Even if it 

 is now and then shaken off" for some distance by a sudden 

 and violent jerking, it makes its appearance again the next 

 moment, always SAvimming again upon the same animal in 

 order to renew its attacks. After some time we observe 

 that the conical base of the smaller Vorticella, which pre- 

 viously projected acutely, becomes retracted, so that a posterior 

 pit is produced, which then frequently sinks so deeply that the 

 posterior circlet of cilia is also retracted or borders the margin 

 of the pit. This pit serves as a sucking-disk^ with which the 



