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.” 
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- 
*"See e. g. Balbiani: Recherches expérimentales sur la mérotomie 
des infusoires ciliés. Recueil Zool. Suisse, t. V, no. 1, 1888. P. 48— 
49, 54; und Verworn: Die physiologische Bedeutung des Zellkerns. 
Archiv fiir die gesamte Physiologie, Band. 41. Bonn, Straup, 1892. 
P. 13—14. 
