94 THE PSYCHIC LIFE 



some portion of the nucleus; in which case the animal 

 reproduces all the organs it has lost in consequence 

 of its dissection. Furthermore, the process of the for- 

 mation is exactly the same as in the spontaneous di- 

 vision of these same Infusoria. The excitation caused 

 by their removal is accordingly of the same character 

 as the unknown excitation that provokes the natural 

 division of the body. 



From these experiments, the part acted by the nu- 

 cleus is indicated by complete evidence. Gruber shows 

 that in a single instance only can a fragment without 

 a nucleus form itself anew; and that is, when the frag- 

 ment contains an organ in course of formation, as hap- 

 pens, for example, during the spontaneous division of 

 the animal. This amounts to saying, that the presence 

 of a nucleus is necessary to give the impulse to the 

 formation of the organ, but that it is not necessary to 

 the completion of the organ when the impulse has 

 once been given. 



Lastly, if the fragment is totally destitute of a nu- 

 cleus, it does not re-form itself so as to constitute a 

 complete animal again; if the fragment possesses nei- 

 ther mouth nor peristome, it does not reproduce a 

 new mouth and a new peristome; yet the fragments 

 continue to live and to move. The absence of a nu- 

 cleus does not suspend the functions of motion, sensi- 

 bility, nutrition, or growth. This conclusion is, in 

 our estimation, too sweeping, as we shall see fur- 

 ther on.* 



M. Balbiani has recently repeated these experi- 

 ments of artificial division, and, while confirming in 



* We have taken as our guide, with the permission of M. Balbiani, the lec- 

 tures delivered by that eminent authority at the College de France, in 



May, 1887. 



