smallwood: maturation of haminea solitaria. 307 



have been observed in other Mollusca, and this same terminology is 

 probably applicable to the structures designated by some writers as sperm 

 asters. 



Upon this question Lillie (:01, pp. 244, 245) says : " Shortly after 

 the metaphase of the second maturation spindle an accessory aster is 

 formed in the egg. It usually arises quite near the center of the egg 

 and bears no fixed relation either to the maturation spindle or the sperm- 

 nucleus ; the center of the aster is occupied by an exceedingly minute 

 centrosome. The latter divides and a small amphiaster is formed which 

 entirely disappears. . . . What is the significance of the accessory aster 1 

 Is it simply due to a renewal of activity of the sperm-centrosomes, which 

 disappeared a cell generation before, or is it an entirely new formation 1 

 1 do not believe that it has anything to do with the original sperm-asters 

 for several reasons : in the first place, there are two sperm-centrosomes, 

 and the accessory aster is at first single and later divides ; secondly, the 

 usual place of origin of the accessory aster does not correspond with the 

 usual place of disappearance of the sperm-amphiaster ; and, finally, in 

 the egg of Crepidula (Conklin, 'gs") tliei'e are two or three accessory 

 asters formed at about this time, wliile the sperm-aster is perfectly dis- 

 tinct in connection with the spern)-head." 



In a former paper (Smallwood, :01, p. 150) I described the conditions 

 represented in text-figure 5 of that article as belonging to the process of 

 fertilization, stating tliat there was a sperm aster. This egg has been 

 examined again (Plate 9, Fig. 59), and the aster found to have no rela- 

 tion to fertilization ; this was the only case in which rays were found 

 associated with the sperm head. I now believe that the asters found 

 in Haminea are to be interpreted as accessory or secondary asters, 

 that they are new, short-lived formations, which do not undergo further 

 development, and bear no relation to the origin of the cleavage 

 centrosomes. 



Byrnes ('99) found only two definite asters in the egg of Limax 

 agrestis during the migration of the sperm head. These asters are 

 termed sperm asters ; but in general appearance, time of occurrence, and 

 position, they correspond to the asters termed accessory by Conklin and 

 Lillie. It seems to me that this is the correct interpretation for these 

 structures in Limax, and that the derivation of the cleavage asters from 

 the sperm asters in Limax is highly improbable. 



The literature of fertilization has been so recently summarized by 

 Coe ('99), Wilson (:00), and Lillie (:0l) that a review of it need not 

 be given here. 



VOL. XLV. — NO. 4 4 



