THE FUXCTION OF THE CEXTROSOME. 2O9 



organs and qualities necessary for division excepting the cen- 

 trosome, by which division is initiated. The spermatozoon, on 

 the other hand, is provided with a centrosome, but lacks the 

 substance in which this organ of division may exert its activity. 

 Through the union of the two cells in fertilization all the essen- 

 tial organs necessary for division are brought together ; the 

 &^g now contains a centrosome which by its own division leads 

 the way in the embryonic development." "It is the centrosome 

 alone that causes the division of the ee^or." ^ 



The behavior of the centrosome in fertilization, as recorded 

 by many recent observers, viay be interpreted as a substantia- 

 tion of Boveri's conclusions, for the centrosomes which are 

 demonstrable in the Qgg during those divisions which result in 

 the formation of the two polar globules totally disappear, and 

 the centrosomes which participate in the first cleavage mitosis 

 arise at any rate near the sperm-nucleus, and, moreover, in 

 many instances are actually brought into the ^g^ by the sper- 

 matozoon (Boveri, Wilson, Matthews, Hill, Fick, Henking, 

 Kostanecki, and Wierzejski, Riickert, and others). In parthen- 

 ogenetic eggs, where no spermatozoon enters, the centrosomes 

 ought, according to Boveri's theory, to remain and to organize 

 the machinery for the first cleavage mitosis. Brauer has shown 

 that the parthenogenetic egg of Artemia fulfills the requirements 

 of this theory, for the &gg centrosomes actually remain and 

 form the cleavage amphiaster. 



These observations furnish ground for the belief that the 

 egg-cells cease dividing, because they lack the active agent 

 in cell-division, — the centrosome. The loss of this or2:an 

 has been regarded as a " provision to guard against partheno- 

 genesis." Thus, according to this interpretation, the rate of 

 cell-division in the cells of at least one generation is conditioned 

 upon the presence of the centrosome. 



Since the essential features of mitotic division are the same 

 throughout the life-cycle, it would seem probable, a priori, that 

 the factors which inhibit or incite the mitotic activity of the 

 egg-cells would also determine whether the cells of other 

 generations should or should not divide. Or, to be more 



1 Boveri, Wilson " Cell." 



