Chromatin as "Hereditary Substance" 333 



term centrosome ought to be ust-d in tlie original sense, the name 

 centriole, used by Heidenhain and others for the central granule, 

 being favored by Hertwig. 



Heidenhain's statement that the centrosome problem has re- 

 eentlv entered a new stage, largely, according to him, through 

 the researches of Yejdovsky and Mra/ek, seems justified by the 

 observations. "Evidently/ 1 says Eieidenhain, "in the eentrosomes 

 of large cells (eggs, blastomeres,) we have to do not with any 

 sort of sharply differentiated bodies of definite organization, not 

 with organs whose capability rests upon a definite, intrinsic con- 

 stitution reached through systematic development, but with strnc- 

 luruJ material transported from place to place through the ac- 

 tivity of the radially differentiated cell substance and heaped up 

 for further use." ~ 



One can hardly avoid reflecting that this statement by Heid- 

 enhain seems to accord much better with the physical-chemistry 

 conception of the cell, that is. with that of the cell as a system 

 of phases in dynamic equilibrium, than with the older idea of the 

 centrosome as in some peculiar way a "dynamic center" of the 

 cell. Nevertheless for the purpose of a general discussion like 

 that in which we are engaged, we may leave the question of what 

 the term centrosome ought to be applied to undecided, and fix 

 attention upon the central granule as belonging structurally to 

 the "cellular center." this phrase being understood to cover a 

 very wide range of objects none of which are simple and some 

 of which are quite complex. 



As to the function of these "centers" there appears to be 

 inimity among the authorities that they are in some wav 

 namic centers of the cell" as originally expressed bv Boveri. 

 'There is some satisfaction in this unanimity even though the 

 range of possibility in "dynamic" is so wide as to make the 

 unanimity rather indefinite. For one tiling, it is certain that 

 the centers take an active and important part in indirect cell 

 division. This is a basal tenet of modern teachings concerning 

 cell division. The role of the centers as force- and activity- 

 produeers which concerns us here is in connection with flagella 

 and movements characteristic of these organs. 



Evidence from the Spermatozoan. 



There appears to he nearly complete agreement among 

 authorities that the axial filament of the tail of the sperma- 



