MUSEUM OF COMPARATIVE ZOOLOGY. 507 



undoubtedly arises directly from the elements of the nuclear plate, and 

 therefore unquestionably corresponds with the " minute corpuscles " in 

 Nephelis, which have a like origin. Furthermore, the behavior of these 

 structures in both snail and worm at the time the first cleavage spindle 

 is forming, as already noted, is significant of their identity. But if they 

 are in reality the same, then some of the arguments advanced by Whit- 

 man will lose in significance when applied to Limax. Size certainly 

 cannot be claimed to indicate their nucleolar nature in Limax, nor will 

 it be at all satisfactory to attribute their ^reat dimensions to the 

 action of such reagents as Biitschli used (acetic acid), since osmic acid 

 confirms the substantial accuracy of the observations in this respect. 

 It remains, however, none the less interesting and important to ascer- 

 tain the cause of the excessive minuteness which these bodies continue to 

 exhibit in Clepsine. I am inclined to think that a causal connection 

 may ultimately be discovered between the diminutive size of these 

 bodies and the segregation of a part of the nuclear substance to form 

 the remarkable polar rings, which, I believe, are not as yet known to 

 exist in other eggs. It is noticeable that the polar globules share this 

 diminutive condition with the corpuscles in question. 



The objections to Biitschli's studies, raised on the strength of Hert- 

 wig's observation that acetic acid does not aiford so reliable results as 

 does osmic acid, are in part valid, as an examination of the figures I 

 have given of Limax will show; but a veritable membrane will hardly 

 be claimed as a necessary part of a nucleus, any more than of a nucleo- 

 lus. Further, the use of chromic and osmic acids clearly shows in the 

 case of Limax (Figs. 52, 68, 70, 72) that these bodies are not perfectly 

 homogeneous, but contain conspicuous structures, not at all to be con- 

 founded with vacuoles, and the reticulum which is characteristic of nu- 

 clei. The evidence of the acetic-acid specimens is in this point, then, 

 substantially corroborated by the use of other reagents. 



The testimony of most recent observers as regards the growth of 

 these bodies at the expense of the surrounding clear substance (central 

 area) is so uniformly the same, that it does not seem necessary to dwell 

 upon this point. It appears to me that an even ^greater obstacle to 

 Whitman's interpretation is afforded by the male pronucleus of Limax, 

 which grows in size at the expense of the surrounding protoplasm with- 

 out the intermediation of any radial system or central area. One is 

 compelled to ask. If the body in question is a male pronucleolus, what 

 evidence have we in Limax of the existence of a male pronucleus? Yet 

 this structure is so entirely similar to what I have called the female 



