220 BYRNES. [Vol. XVI. 



extrusion of the second polar globule the eggs regained their 

 normal outline. In some of these abnormal eggs the egg- 

 nucleus and sperm-nucleus remained permanently separated, 

 although both had attained their maximum size. 



The sperm-nucleus is sometimes held fast to the egg-mem- 

 brane at the lower pole, or it may have penetrated only half- 

 way into the tgg. While the sperm-nucleus is thus retarded 

 in its advance toward the egg-nucleus, the two spherical bodies 

 appear. PL XII, Figs. 41 and 42, show two sections through 

 different regions of the same Qgg. The section in PL XII, 

 Fig. 41, which is the last of a series, falls through the sperm- 

 nucleus on the side away from the egg-nucleus, and shows the 

 sperm accompanied by the two distinct bodies. These bodies 

 behave differently toward different staining reagents. This 

 Qgg was killed in corrosive sublimate acetic acid (5 per cent) 

 and hardened in Flemming's solution. When stained in 

 Heidenhain's haematoxylin, the bodies appear as deeply stained 

 homogeneous structures with well-defined outlines ; but in borax- 

 carmine and Lyons blue they are highly refractive and almost 

 colorless. Around one of these bodies is a slightly denser 

 layer of protoplasm, which bears out the suggestion that they 

 may be centers of attraction. There is, however, no radi- 

 ate structure around either of them. Nevertheless, their late 

 appearance, their connection with the sperm-nucleus, their be- 

 havior towards staining reagents, their number and general 

 structure make the suggestion irresistible that they may be due 

 to the presence of the centrosomes which have taken this pecu- 

 liar form under abnormal conditions. If these conclusions be 

 well founded, these abnormal ova furnish important evidence in 

 regard to the nature of the centrosome in Limax, for they show 

 that centrosomes may exist as definite structures in the e.gg apart 

 from the rays which usually mark their presence. 



IV. Formation of the Spindle. 



Soon after the apposition of the egg and sperm-nuclei the 

 chromatin becomes arranged along the nuclear filaments that 

 lie in the long axis of the forming spindle (PL XII, Figs. 36 



