44 KINGS LEY. [Vol. VII. 



I am in doubt as to the interpretation of these phenomena. 

 They are not connected with segmentation. Two possibilities 

 have suggested themselves. One is that they may possibly 

 be compared with those still unexplained polar rings described 

 by Whitman ('78, p. 234), on both poles of the maturing o^^g 

 of Clepsine (a suggestion of doubtful value). The other would 

 view them as connected with the formation of the blastema. 

 It is certain "that a blastema surrounds the egg of Limulus after 

 this process while none was visible before. 



In one 0.%^ of about twelve hours I found what I regarded in 

 my preliminary paper ('90) as the segmentation nucleus, occupy- 

 ing a subcentral position in the yolk, but I have not succeeded 

 in connecting it with the later stages. In other eggs of the 

 same age I find a thickening of the blastema on one side of 

 the egg, but no stain serves to distinguish a nucleus in it, but 

 still it may be present. The position of the segmentation 

 nucleus has no great taxonomic importance, as in both Crustacea 

 and Arachnida it may be either subcentral or superficial.^ 



Stage A. — Between twelve and twenty hours I have not 

 been able to get any sections showing anything. At twenty 

 hours I found an ^gg containing eight nuclei. By drawing 

 these in their relative positions and projecting them on a plane 

 (Fig. 9), a marked polarity in their distribution is apparent. 

 As will be seen, the nuclei are much nearer to one pole of 

 the Qgg than to the other, and had the plane of projection 

 been slightly different this polarity would have been more 

 marked. This condition is intelligble on the view that the 

 segmentation nucleus is subcentral as well as if it be regarded 

 as superficial. 



In the next twenty hours there are no phenomena to detail at 

 length. From the surface no changes are visible, while sections 

 reveal a gradual increase in the number of nuclei, the polarity 

 just mentioned persisting in their distribution. 



blastema may exist without nuclei. The term blastema was first used by Weismann 

 ('63) for a non-nucleated layer in Musca and Chironomus, and such a layer has 

 been shown to exist in many eggs by various authors, among them Metschnikoff 

 ('66) in Aphis, Aspidotus, Csecidomyia; Witlaczil ('84) in Aphis; Locy ('86) in 

 Agalena; Heider ('89) in Hydrophilus; Voeltzkow ('89) in Musca, etc. A 

 blastema, then, is a layer of anucleate protoplasm around the yolk. 



1 E.g. subcentral in Cetochilus (Grobben, '81), Crangon (Kingsley), Eupagurus 

 (Mayer, '77), Porcellio (Reinhard, '87), Araneina; peripheral in Nebalia (Metschni- 

 koff), Mysis (Van Beneden, '69), Scorpio (Laurie), Acarina (Claparede, '68). 



