OF MICR O- OR G AN I SMS. 1 1 9 



other one of the capsules produced by the division of the nucleolus, 

 so that when we come to the phase of the process represented in 

 figure C, we find an animal which contains, besides its nucleus, two 

 nucleolar segments in immediate proximity (mf #'); it was the 

 same in figure B; each animal already possessed two nucleolar seg- 

 ments, but these segments were obtained from the division of the 

 nucleolus properly belonging to the animal itself, while in figure C, 

 in consequence of an exchange effected, one of the nucleolar seg- 

 ments belongs originally to each animal and the other comes from 

 its mate. 



M. Balbiani, who made the first observations upon these phe- 

 nomena of a nature so delicate and complex, originally supposed 

 that the two adjacent nucleolar segments, which have been rep- 

 resented in the figure C, were produced by the longitudinal di- 

 vision of the nucleolus exchanged between the two animals in con- 

 jugation. 



M. Maupas has recently proposed a different explanation, 

 which seems to be further corroborated by the very figure given 

 twenty years previously by M. Balbiani. According to M. 

 Maupas the segment exchanged proceeds to fuse with the segment 

 not exchanged, in order to form a compound segment; the two con- 

 tiguous segments, seen in figure C, would not, therefore, be the re- 

 sult of the division of one segment solely, but the first stage of the 

 conjugation of two elements having different origins. A fact which 

 apparently argues in favor of this opinion, is the aspect presented 

 by the two segments; if they proceed from a division, we would 

 find there certain phenomena of caryokinesis, which were further- 

 more completely unknown at the time when M. Balbiani made his 

 first observations. 



However this may be, it is seen by figure C that the regression 

 of the old nucleus (n) is sharply marked. 



In the figure D, the two nucleolar segments have fused to- 

 gether and have formed a compound segment, which segmentates in 

 its own turn; the two new products of that segmentation grow to 

 unequal sizes; the largest capsule attains a size of forty thou- 

 sandths of a mm. ; it is this that forms the new nucleus of the 

 Chilodon. The second capsule shrinks and becomes compressed, 

 it takes its place beside the first one and becomes the new nucleolus. 



The figure E represents the last stage of the phenomenon; the 

 animal is in possession of its new nucleus and its new nucleolus; 



