No. 584] 



HEBEDITT AND ITS MEANING 



459 



This belief may be too radical. The machine must have 

 all of its parts to do proper work; and it may be, as Conk- 

 lin suggests, that such characters as polarity, symmetry 

 aud localization of organ bases in the egg have their chief 

 seat in the cytoplasm. This is only a possibility and not 

 a fact, however, for one must admit that cytological inves- 

 tigation has not disclosed the presence of a material basis 

 of heredity in the cytoplasm, though he may not be con- 

 vinced that it is unimportant. Does the same statement 

 hold for the nucleus ! 



The nuclear cavity contains four substances as they are 

 ordinarily described in connection with morphological in- 

 vestigations. These are nuclear sap, linin, nucleolar ma- 

 terial and chromatin. 



Nuclear sap probably belongs as much to the cytoplasm 

 as to the nucleus, and we know nothing as to its possible 

 significance and importance within the nucleus. 



Linin by some investigators is regarded as very similar 

 to chromatin. Others (Strasburger) consider it to be 

 the framework of the chromosomes, and the only real sub- 

 stance within the nuclear cavity that is continuous from 

 generation to generation. It is a thread-like material 

 staining lighter than chromatin upon which the chromo- 

 somes appear to be strung in the early prophases of nu- 

 clear division. 



Nucleolar substance, though it stains in a different 

 manner from chromatin, is considered by many to be 

 chromatin-like in its nature. It is the substance of which 

 the nucleoli are composed; but as these bodies become 

 vacuolated and finally disappear during nuclear division, 

 one is led to believe with Strasburger that they are tem- 

 porary storehouses of some necessary food material. 



Chromatin, however, as the material of which the 

 chromosomes are composed, plays such a peculiar part in 

 the activities of the cell, that hypotheses as to the mean- 

 ing of its behavior are certainly more than shrewd guesses, 

 as will he seen. 



The chromosomes may be described as morphological 



