222 bulletin: museum of comparative zoology. 



ing- on the question of the limits of the centrosphere. Other instances 

 of this phenomenon will be referred to farther on. 



It will be remembered that no centrosome, as that structure is gen- 

 erally understood, is to be made out in connection with the first matu- 

 ration spindle of Limax maxim us. After the formation of the first polar 

 cell, however, we have (in Figures 17 and 21) within the centrosphere 

 the centrosome already divided, presumably in preparation for the 

 formation of the second maturation spindle. In Figure 17 the centro- 

 somes are extremely small, and only one of them gives indication, even 

 with the best immersion lens, of having rays in connection with it, but 

 in Figure 21 the small dense bodies have all the characteristics of 

 centrosomes. Although the centrosomes in Figure 21 are very minute, 

 they may still be made out with certainty at points from which several 

 very delicate rays diverge. These rays may have some connection with 

 rays outside the reticulated area, but if they do, it is only a secondary 

 connection. The rays extending from either centrosome toward the 

 other have uiiited into a very small but fairly distinct spindle (not well 

 shown in the figure). 



(6) Second Maturation Spindle. 



My study of Limax maximus points to the conclusion that after the 

 formation of the first polar cell, and possibly during that process, the 

 centrosphere remaining in the egg increases in size to many times 

 the volume it had in the first maturation spindle. Neither after the 

 formation of the first polar cell, nor after the formation of the second, 

 have I been able to trace continuously the modification of the centro- 

 sphere. In Figure 20, however, the periphery of the centrosphere is 

 very faint ; and it seems as if the whole structure were on the verge of 

 disappearance. In a subsequent part of this paper I shall take up the 

 discussion of the fate of the inner centrosphere and also the centrosome 

 of the second maturation spindle. 



2. LiMN^A Elodes. 



(a) First Maturation Spindle. 



My observations on the first maturation spindle of Limnnca elodes 

 have resulted in a number of interesting facts bearing on the relation of 

 centrosphere to centrosome. As stated in the introduction, the centro- 

 some sometimes appears stained faintly, sometimes very deeply. "When 

 deeply stained, it varies .in size from an extremely small body to one of 



