3T4 ISTaohide Yatsu. 



of tlio germ nuclei, and that at this particular period the centro- 

 plasm is fixed always very poorly. i\ny one who has had experience in 

 fixing has surely noticed that the same treatment acts differently upon 

 different lots of eggs according to their "physiological state" so to 

 speak. (Mrs. Andrews, '97, pp. 16, 31.) Even in one and the same 

 lot one finds eggs excellently fixed side by side with poor ones. 

 Especially at the moulting stage the centriole is extremely sensitive 

 towards fixing fluids. Wilson ('Ola) expresses the difficulty in fixing 

 the centrioles at the division stage of the aster. Vejdovsky and 

 Mrazek ('03) state that they could not follow the division of the 

 sperm centriole owing, I imagine, to the impossibility of getting 

 satisfactory fixation at his particular stage (pp. 502-503). Tak- 

 ing into account the above difficulty in fixation it is certain that 

 the sperm centrioles pass through a stage when they are liable to be 

 destroyed by fixing fiuids. Only such centrioles as happen to regain 

 their activity at an earlier period, and come to be less susceptible to 

 the fixing fluid, can escape from l)oiug dissolved (cf. Wilson, '00, p. 

 214). Despite the temporary disappearance of the sperm centriole, 

 I conclude, therefore, that tlie cleavage centrioles are identical tuitli 

 the sperm centrioles (Kostanecki, '06, p. 60). 



(cZ) Division of the Centrosome. 

 1. Observations. 



For the study of the moulting of the centrosome, no stages can be 

 better than the formation of the second cleavage centrosomes. This 

 process begins in C. lacteus at a late prophase of the first cleavage 

 mitosis. The centriole becomes double at the end of the spindle. 

 The centrosome at this stage has not increased in size (PL III, Fig. 

 47). It should here be noted that the division of the centriole and 

 the increase of the centrosome are two independent phenomena. The 

 centriole divides irrespective of the spindle axis, e. g., perpendicular 

 in Fig. 47 (PI. Til), and obliquely in Fig. 50 (PI. Ill) (cf. Boveri, 

 '00, p. 43). Neither does the division ])lane coincide with the short 

 axis of the centrosome (PI. Ill, Fig. 50). In the meanwhile en- 



