310 Naohide Tatsu. 



where they acquire rays and thus give rise to the cytasters. Apart 

 from the fact that neither of these assumptions is supported by 

 any direct observations they contradict the definition of the cen- 

 trosome as given by Boveri ('oi, pp. 132, 162, etc.) that the organ 

 is single (or double by anticipation). A multiplication of cen- 

 trioles capable of producing centrosomes is nowhere known to take 

 place unless it be in abnormal or degenerating cell, such as the 

 giant cells or the oligopyrenous spermatozoa. It may be said 

 that centrosomes (centrioles) arise by the enlargement of ultra- 

 microscopical granules or plastids that coexist with the visible 

 astral centriole. This is quite possible, but if visible centrioles 

 may thus arise in addition to the visible ones already existing and 

 mdependently of them centrosome formation de novo in the ordinary 

 sense of this expression is demonstrated none the less. The results 

 of my cutting experiments, therefore, I believe, lead us to the 

 unavoidable conclusion that the centrioles are formed de novo, 

 as Wilson mamtained. 



In conclusion one word about the nature of the sperm centriole. 

 One might be readily led to infer from what I have said that the 

 sperm centriole in the normally fertilized egg may arise in the 

 same manner as those found in the cytasters. In Cerebratulus, 

 at least, this is not the case, for I have been able to show that the 

 centriole, as such, is actually brought into the egg in the middle 

 piece of the spermatozoon. Detailed evidence in support of this 

 statement will be published hereafter. 



VII. SUMMARY. 



1. When subjected to the action of a solution of CaClj enu- 

 cleated fragments of unfertilized egg of Cerebratulus lacteus, 

 obtained by cutting the eggs singly at the metaphase of the first 

 maturation mitosis, develop true asters containing central bodies. 

 The corresponding nucleated fragments show the typical matura- 

 tion spindle. 



2. Cytasters do not, however, appear in enucleated fragments 

 from unfertilized eggs before the fading of the germinal vesicle. 



3. The central bodies of the cytasters developed in enucleated 

 fragments are centrioles identical in structure with those in the 

 nuclear asters of whole eggs similarly treated. 



