Physiology and Biology of the Protozoa. 477 



induces the animals to divide, and the irritation caused by 

 the violent removal of a part of the body, are identical in 

 their effects. In the regeneration of the lost organs and por- 

 tions of tissue in the higher animals we have essentially the 

 same phenomenon, only with this difference, that in the latter 

 the cells perform what in the Infusoria is performed by the 

 elementary particles, micellae, or what we choose to call them. 

 If we ascribe regeneration in the Metazoa to the influence of 

 embryonally formed cells, we must here award the function of 

 new-formative elements to originally -formed micelloi, which, as 

 we shall see hereafter, are subject to the directing influence of 

 the nucleus. 



I believe that I can show in the case of Stentor that the 

 process of regeneration is a regular one and homologous with 

 the well-known process of new- formation in spontaneous 

 fission. We might conceive that in every Infusorian at a 

 certain time the materials for the organs of a new animal are 

 prepared and stored up in the interior, and at the given 

 moment begin to group themselves ; in the artificial division 

 of an Infusorian in this stage, and therefore ready for sponta- 

 neous division, a process, which would have occurred at this 

 moment as the new formation preceding spontaneous reproduc- 

 tion, would appear to us to be regeneration. But this is not the 

 case ; for, in the first place, it is very improbable that all the 

 Stentors employed in the experiments were precisely in the 

 same stage of development ; and, in the second place, I have 

 often divided such as had just been produced by spontaneous 

 fission, or were still engaged in that operation, and these ha*^e 

 also become regenerated, which would not have been possible 

 upon the above hypothesis, as the reserve-material in them 

 would just have been used up. Regeneration, therefore, can 

 be due only to a conversion of elementary parts already present, 

 taking place rapidly upon e.vternal irritation. 



As regards the degree of the rege7ierative faculty , this is very 

 high in Stentor ; and no particular part of the body appears to he 

 specially disposed thereto, hut all parts of the body react in the 

 same way. 



This is clear from the following experiments : — 



If we cut away the extremity of a Stentor far behind the 

 middle of the body, this extremity has the same regenerative 

 faculty as one the cut surface of v\^hich was near tlie anterior 

 end ; or, further, if we divide a Stentor first of all by a longi- 

 tudinal incision into right and left halves, and divide each of 

 these two pieces again into an anterior and a posterior portion, 

 or, which answers still better, make the transverse section 

 first and the longitudinal ones afterwards (fig. 3), all the four 



