234 INFUSORIA. 



and very cogent reasons for the comparison of the Infusorian body with 

 a cell. The investigations of this excellent observer prove that changes 

 of the nucleolus, quite similar to those above described, may often 

 be observed in the nuclei of ordinary dividing cells and segmenta- 

 tion masses. The ordinary supposition that in division the nucleus of 

 the cell simply separates into two parts was shown to be a mistake, due 

 partly to the variable and often unfavourable condition of the material 

 examined, but much more to the minuteness of the object and the use 

 of insufficient microscopic power. In reality the process is a compli- 

 cated one, accompanied by a transformation of the contents, which 

 essentially resembles the formation of nuclear fibres in the Infusoria. 

 After this phenomenon was once recognised, it was repeatedly observed 

 with various modifications in the most diverse kinds of cells (also by 

 Strasburger in vegetable cells), and was in fact proved indubitably to 

 be of general occurrence. The apparent " sperm-balls " were therefore 

 divided nuclei, which afterwards reassume a homogeneous nature, and 

 the so-called " sperms " were anything but what Balbiani and Stein l 

 had supposed. 



The Nucleolus of the Infusoria is thus a structure which, in its 

 essential morphology, coincides with the nucleus of the ordinary cell, 

 and may therefore be justly identified with it. It is not, then, sexual 

 maturity which finds expression in its transformation, but simply the 

 commencement of division, which, as a matter of fact, follows close 

 upon the process of conjugation. This mode of multiplication is not, 

 however, confined to the time immediately following conjugation. It 

 also occurs later, but happens most frequently and constantly in those 

 forms which have previously conjugated. So far as we know, this 

 process and its modifications (including budding) is the only mode of 

 reproduction exhibited by the Infusoria. 



But if, as we have maintained, the " nucleolus " represents the 

 nucleus of the Infusorian body, what, then, is the " nucleus " to which 

 this position is usually accorded ? Again the process of conjugation 

 sheds light on the question. The observations on this point, especially 

 of Blitschli, inform us of the surprising fact that the portions of the 

 "nucleus" are indeed, as Balbiani affirmed of his "eggs," generally 

 expelled during conjugation, without, indeed, ever forming new indi- 

 viduals. Instead of this expelled " nucleus," another is formed, and 

 that from one of the newly originated " nucleoli." Sometimes the 

 portions of the " nucleus " are not wholly expelled, and then the new 

 " nucleus " results from a fusion of the remainder with a " nucleolus." 



1 To establish the theory of these investigators it would have been necessary to prove 

 that the sperms resulted from cells. But no one had tried to discover a cellular struc- 

 ture in the nucleolus. 



