Ookinesis in Cerebratulus Lacteus. 373 



2. Cleavage Centriole. 



After the format ion of the cii'i;' nucleus, the egg ceutriole lingers 

 for a little while in a niche of the nucleus, but it soon disappears, 

 (PI. IV, Fig. GS). The sperm nucleus, with two asters connected 

 by a spindle comes in contact with the egg nucleus not far from the 

 place where the latter was formed. The asters sometimes precede 

 (PI. Ill, Fig. 41), sometimes follow the spenn nucleus (PL III, 

 Fig. 42) (cf. Coe, '1)9, p. 447, Kostanecki, '06, p. 17). At the time of 

 the conjugation of the germ-nuclei or a little later, the sperm asters 

 become irregular, the rays curving like a fountain (PI. IV, Fig. 08). 

 Singularly enough no considerable increase of the centroplasm takes 

 place. The ceutriole may take any place in the degenerating cen- 

 trosome — in many cases away from the centre of the rays ; some- 

 times close to the nuclear walls, sometimes quite far from it. This 

 fact suggests strongly that there may have been a current in the 

 cytoplasm at the conjugation of the germ-nuclei. 



In order to decide the origin of the cleavage centrioles, I have 

 studied serial sections of t^venty-three eggs at the stage when previous 

 observers lost the centrioles in the egg of C. maifjlnatus (Coe, '99, 

 Kostanecki, '02). The result was that six eggs show two centrioles, 

 fourteen eggs one ceutriole and three eggs none. Figs. 43 and 44 

 show the sections of the egg in which two centrioles are found at the 

 critical period. Xve the two centrioles new formations or the same 

 ones as those in the sperm astern ? It is extremely difficult to decide 

 this question owing to the fact that one cannot follow the history of 

 the centrioles in the living eggs. But it is clear that these centri- 

 oles are not on their way to degeneration, but they have recently 

 acquired new activity since they have a small ray system around 

 them. Prior to the conjugation of the germ nuclei, the centrioles 

 are invariably present (PL III, Figs. 41 and 42), and in some cases 

 the centrioles have come to possess a new ray system even before the 

 coming together of the germ nuclei (PL III, Fig. 45^ (Coe, '99, pp. 

 451 and 457). From this it may be concluded that in some cases 

 the spenn centrioles survive throufjJi the critical period, v^hile in 

 many they disappear during this stafje. It should here be noted that 

 the centrioles dwindle considerably in size just before the conjugation 



