54 Indications of a Central Zone of Development 



other fragments, without nuclei, are incapable of it even 

 though they may be much larger. 



Especially we recall the researches upon artificial di- 

 vision of the Infusoria made by Nussbaum and Gruber. 

 If, for example, one cuts a stentor into three pieces, of 

 which each contains one portion of its moniliform nucleus, 

 in the space of twenty-four hours each piece regenerates 

 the missing part. The anterior extremity regenerates the 

 posterior and vice versa ; the middle piece reforms the two 

 extremities, that is to say, both the rather complex peri- 

 stomal region with its mouth, its pharynx, its long cilia, 

 etc., and also the simpler posterior part. If however the 

 fragment retains no part either of the paranucleus or of 

 the nucleus proper, even though it may be of much 

 greater size than those fragments retaining the nuclei, no 

 trace of regeneration is observed, a fact which does not 

 prevent the piece concerned from continuing to live for a 

 while, even for two or three days, nor from retaining com- 

 pletely the capacity of locomotion, of vibration of cilia, 

 of pulsation of the contractile vesicle, of defecation, of 

 capturing, engulfing and digesting its food. 27 



Gruber reports however the following experiment 

 which has caused a good deal of surprise, for according 

 to the view of some biologists it seems to be opposed to 

 the results of earlier researches. 



He selected a Stentor coerelus which showed already 

 the first stages of spontaneous division, that is there had 

 already commenced in it the formation of a lateral, per- 



27 See e. g. Balbiani : Recherches experimentales sur la merotomie 

 des infusoires cilies. Recueil Zool. Suisse, t. V, no. I, 1888. P. 48 

 49, 54; und Verworn : Die physiologische Bedeutung des Zellkerns. 

 Archiv fur die gesamte Physiologic, Band. 41. Bonn, Strau/3, 1892. 

 P. 1314- 



