372 ISTaohide Yatsii. 



that the sperinatozooii of Alldohoplioni foetida contains two cen- 

 trioles at each end of the middle piece, and the posterior one persists 

 as the sperm centriole ('03, p. 300). In Cerchmtulus lacteus, as we 

 have already seen, it is rather easy to trace uninterruptedly the cen- 

 triole from the young spermatozoon to that of the sperm aster, owing 

 to the fairly large size of the centriole and the vesicular nature of the 

 middle-piece (Yatsu, '07). 



As to the fate of the middle piece in the egg. In most forms, I 

 think, the middle-piece fades in situ as soon as it enters the egg, thus 

 leaving the centriole free in the ooplasm. The rapid degeneration of 

 the middle-piece nudges it in most cases almost impossible to follow 

 its history in the egg. The throwing-off of the middle-piece or, in 

 other words, the escape of the centriole from the middle-piece, seems 

 to me a very rare phenomenon. Besides C. lacteus this has been 

 observed in only one form.^^ In Toxopneustes variegatus Wilson, 

 ('97, '99, '00, p. 188, Fig. 12) observed that the middle-piece be- 

 comes detached from the nucleus and is cast to one side, as a dark 

 staining granule that degenerates in situ. The rays focus at the basal 

 point of the nucleus, where the centriole appears ('99, p. 14). 

 Whether the centriole lies in the middle-piece or between it and the 

 nucleus he was not able to determine ('97, p. 371). 



The question naturally arises as to whether the centriole or the 

 centriole and centrosome together are brought into the egg by the 

 spermatozoon. -"^^ But in Cerehratulus lacteus the condition is quite 

 different. The granvde found in the middle-piece is a little larger 

 than the ordinary centriole, it is true, but just after its escape from 

 the middle-piece it has no centrosome at all. Even if the centrosome 

 be present in the middle-piece, it must degenerate in the ooplasm. 

 In our case at least, it may safely be concluded that the centi'osome 

 in the sperm aster is derived from the egg substance. 



"Field ('95) states that in Asterias llie separation of the middle piece 

 (mitosome) near the place of entrance into the egg as was observed by 

 Pictet and Cuenot (p. 22.5). But judging from his statement that the spermato- 

 zoon devoid of the mitosome is capable of fertilization, the nature of this body 

 can be questioned. 



'''Boveri's figures represent spermatozoa already rotated. The sperm-htjad 

 with naked centrioles might be found before its rotation. 



