Physiology and Biology of the Protozoa. 481 



rative power as we have demonstrated, for example, in Stentor^ 

 this question is not so easy to answer ; for when living freely 

 they will rarely have to suffer injuries, or at all events such 

 injuries as we can inflict upon them artificially with the 

 scalpel. In multicellular animals this is quite otherwise ; in 

 their case we know that they have very often lost parts of 

 their bodies by violent attacks, and in their case we are not 

 surprised that many of them are endowed with a very highly 

 developed regenerative capacity, which has to play an important 

 part in the preservation of the species. But what is the case 

 in the Protozoa ? In my preliminary communication I have 

 already expressed the opinion that perhaps the acquisition of 

 the regenerative facility by the Infusoria [and by the Protozoa 

 in general^ may depend, on the fact that they frequently break up 

 spontaneously into irregular fragments^ and that then many 

 of these fragments are able to become developed again into 

 normal animals. 



This spontaneous breaking up is a phenomenon easy of 

 observation in the life of the Infusoria, and one that I have 

 already seen in a number of species ; it struck me particularly 

 in the case of a colony of Oxytricha, and in this, among the 

 ruins which circulated in the water, I found many which were 

 indeed much smaller than the normal animals, but still more 

 or less regularly formed, so that we may assume that here a 

 regeneration had taken place. I do not venture to draw any 

 more certain conclusion, because at the time I had something 

 else in view, and did not go into this point with sufficient 

 exactness. In other Infusoria, however, the breaking up of 

 the body into small fragments and the subsequent growth of 

 these into normal animals is a regular phenomenon and the 

 ordinary mode of increase, namely in the Opalince. It is 

 remarkable, however, that these are precisely the Infusoria 

 which, as already mentioned, could not be artificially multi- 

 plied ; but this does not seem to me to be inexplicable, as the 

 Opalinoi^ as is well known, are Entozoa, and their natural 

 conditions of existence could hardly if at all be realized for 

 them during the experiment. 



If we accept as possible the faculty of the Infusoria to 

 break up spontaneously and to rise again anew from the ruins, 

 we get for them conditions exactly analogous to those of the 

 Metazoa, as may be shown by an example already mentioned 

 by me : — A worm (e. g. Nais) can divide spontaneously into 

 two equivalent individuals, just like an Infusorian ; a worm 

 (e. g. Gtenodrilus monostylos *) can break up spontaneously 



* Zeppelin, "Ueber Ban und die Tlieilimgsvorgange des Ctenodrilus 

 rnonostylos," in Zeitsclir. f. wiss. Zool. Bd. xxxix. (1883). 



