354 CELL-CllEMISTKY AND CELL-PIIYSIOLOGY 



hand, undergoes a special differentiation in each to effect a second- 

 ary division of labour between the germ-cells. When this is corre- 

 lated with the fact that the germ-cells, on the whole, have an equal 

 effect on the specific character of the embryo, we are again forced 

 to the conclusion that this effect must primarily be sought in the 

 nucleus, and that the cytoplasm is in a sense only its agent. 



C. The Centrosome 



E.xisting views regarding the functions of the centrosome may con- 

 veniently be arranged in two general groups, the first including those 

 which regard this structure as a relatively passive body, the second 

 those which assume it to be an active organ. To the first belongs the 

 hypothesis of Heidenhain ('94), accepted by Kostanecki ('97, i) and 

 some others, that the centrosome serves essentially as an insertion- 

 point for the astral rays ("organic radii"), and plays a relatively 

 passive part in the phenomena of mitosis, the active functions being 

 mainly performed by the surrounding structures. To the same 

 category belongs the view of Miss Foot that the formation of the 

 centrosome is, as it were, incidental to that of the aster — "the 

 expression, rather than the cause, of cell-activity " ('97, p. 810). To 

 the second group belong the view^s of Van Beneden, Boveri, Biitschli, 

 Carnoy, and others who regard the centrosome as playing a more 

 active role in the life of the cell. Both of the former authors have 

 assumed the centrosomes to be active centres by the action of which 

 the astral systems are organized ; and they are thus led to the conclu- 

 sion that the centrosome is essentially an organ for cell-division and 

 fertilization (Boveri), and in this sense is the "dynamic centre" of 

 the cell.^ To Carnoy and Biitschli is due the interesting suggestion ^ 

 that the centrosomes are to be regarded further as centres of chemical 

 action to which their remarkable effect on the cytoplasm is due. 

 That the centrosome is an active centre, rather than a passive body 

 or one created by the aster-formation, is strongly indicated by its 

 behaviour both in mitosis and in fertilization. Griffin ('96, '99) points 

 out that at the close of division in T/ialassevia the daughter-centro- 

 somes migrate away from the old astral centre and incite about 

 themselves in a different region the new^ astral systems for the 

 ensuing mitosis (Figs. 99, 155); and similar conditions are described 

 by Coe in Cerebratnlns ('98). In fertilization the aster-formation can- 

 not be regarded as a general action of the cytoplasm, but as a local 

 one due to a local stimulus given by something in the spermatozoon ; 

 for in polyspermy a sperm-aster is formed for every spermatozoon 

 (p. 198). This stimulus is given by something in the middle- 



1 Cf. pp. 76, 192. ^ <7^ p- "o- 



