Ookinesis in Cerebratulus Laetens. 367 



that the diiDlosome is a compound structure, i. e., a centrosome con- 

 taining a centriole in it (cf. Boveri, '00, p. 93). This argument is 

 not valid, since the same can be said of the ordinary centriole in 

 the centrosome. Who can demonstrate that the centriole in the latter 

 case does not have a thin coating of centroplasm about it ? 



(c) History of the Centriole in Fertilization and in Cleavage. 



I have demonstrated elsewhere (Yatsu, '04, '05) that centrioles 

 can be artificially produced by a salt solution and verified the con- 

 clusion reached by Wilson ('01) that the centrioles can be formed 

 de novo in cytoplasm. In other words, after the dissolution of the 

 germinal vesicle the protoplasm has an inherent power of produc- 

 ing centrioles, Avhich is inhibited under normal conditions, and is 

 called forth only by a favorable stimulus. 



The results of my study of the fertilization of C. lacteus excludes, 

 however, the view that the sperm-centriole is of egg-origin and is 

 produced de novo by the action of the spermatozoon (cf. Morgan, 

 '00, p. 506). The spermatozoon in oar case actually brings into 

 the egg the sperm-centriole, which later gives rise to the cleavag& 

 centres and those of suhsequent divisions. 



1. Sperm Centkiole. 

 (a) Observation. 



A mature spermatozoon is represented in PI. II, Fig. 20. A 

 slender slightly curved head is followed by a tail a little less than 

 six times as long as the head. In well extracted preparations one 

 observes that the middle piece is a vesicle containing a dark stain- 

 ing axis and a distinct granule near the posterior end (PL II, Fig. 

 21).^^ The subsequent history of the granule shows that it is really 

 a centriole and not a structure produced by concentric extraction, 

 as I ascertained by watching every stage of the differentiation by 

 iron-alum. The granule, it should be noted, resists extraction even 

 until the time the head becomes light blue. In a young spermato- 



"Retzius ('04) failed to differentiate tills grannie in the spermatozoon of 

 MalacolydeUa grossa (his Figs. 20-27). 



