,12 



SOME VKOBLEMS OF CELI -ORCAXI ZA'JIOS 



cotte, Van der Stricht, Meves, and others apply the term to the central 

 granule or granules plus the surrounding sphere (" centrosome " of 

 Boveri), which they regard as equivalent to the medullary zone of 

 Van Bcncdcn, the " corpuscule central " of the last-named author 

 being identified with the central granule or "centriole" of Boveri, 

 though the latter structure is considerably smaller than the former 

 as described by Van Beneden. 



The matter of fact turns largely on the question whether the astral 

 rays traverse the larger sphere to the central granule. That such is 

 the case in Ascaris is positively asserted by Kostanecki and Siedlecki, 

 l_'97) and as positively denied by Fiirst ('98) with whose observations 



Fig. 153. — Structure of the centrosome in the polar asters of a gasteropod, Diaulula. [MaC- 

 Farland.] 



A. Mitotic figure, formation of first polar body. B. Inner aster at final anaphase; central 

 granule double within the " centrosome." C. Elongation of old " centrosome " to form second 

 polar spindle. 



those of MacFarland ('97) on gasteropod-eggs agree. On the other 

 hand, in the turbellarians the observations of Francotte ('97, '98) and 

 Van der Stricht ('98, i) seem to leave no doubt that the larger sphere 

 ("centrosome"), here very sharply defined and staining deeply in 

 iron-haematoxylin, is traversed by well-defined astral rays converging 

 to the central corpuscle, and both these observers agree further that 

 both the corpuscle and the sphere divide to persist as the " centrosomes " 

 of the daughter-cells — a result in conformity with Van Beneden's con- 

 clusion in the case of Ascaris. 



Lillie's valuable observations on the polar asters of Utiio ('98) afford, 

 I believe, conclusive evidence as to the nature of the sphere. In the 



