48 BIOLOGY OF THE PROTOZOA 



and regenerate the lost part, while the enucleate portion will con- 

 tinue to move and manifest various activities characteristic of 

 destructive metabolism, but it will not take in food, nor digest what 

 food may have been taken in before cutting and in the course of 

 a week or ten days it dies (Hofer, Verworn, Balbiani and many 

 others) . 



It is evident therefore that chromatin is directly associated with 

 all of the important vital activities including reproduction, and the 

 view has been repeatedly advanced that, for these varied activities 

 at least, two different kinds of chromatin are responsible. One 

 kind, the so-called vegetative or trophochromatin, is active in the 

 ordinary metabolic functions of the cell, while the other, the ger- 

 minal or idiochromatin, has to do solely with perpetuation of the 

 race. While this view of the dual nature of chromatin would seem 

 to be sustained by the phenomena in rhizopods and by the dimorphic 

 nuclei in the ciliates, it is by no means assured that this duality 

 represents a fundamental difference in chromatins. On the con 

 trary it is much more probable, as Hertwig has maintained, that 

 there is only one chromatin and that its functional activity depends 

 upon different factors and conditions which may arise during the 

 life cycle; germinal chromatin in one cell-generation may become 

 vegetative chromatin in the next and vice versa. This is particularly 

 clear in the case of the ciliates where the macronucleus, a distinctly 

 vegetative nucleus, and the reproductive micronucleus, arise as 

 subdivisions of a fertilization nucleus after conjugation or its equiva- 

 lent parthenogenesis. 



The importance of chromatin for life of the cell is indirectly indi- 

 cated by the extreme precision with which it is distributed to 

 daughter cells at the time of division. Like other granules of the 

 cell each chromomere grows and reproduces its exact duplicate by 

 division. Chemically it probably represents the pinnacle of complex 

 structures formed as a result of the activities of constructive meta- 

 bolism while its derivatives, likewise granular in form and difficult 

 to distinguish as such, formed by reductions, deamidizations and 

 other chemical processes, give rise to many more or less permanent 

 or temporary structures in the cell body, each of which may per- 

 form some cellular activity in its passage through the various stages 

 of disintegration. 



2. Chromidia." As stated above, chromidia are only chromatin 

 granules distributed in the cytoplasm, and the main significance 

 in the term as we use it today is to indicate the extra-nuclear posi- 

 tion of chromomeres. They have come to be regarded as character- 

 istic structures of the protozoon cell, however, and students of the 

 Protozoa speak of chromidia with the same familiar ease that they 

 do of the nucleus. In some types a definite nucleus is entirely 

 absent and such forms provide the only justification for Haeckel's 



