2l6 BYRNES. [Vol. XVI. 



centrosomes first appear in the eggs of Limax, they are so 

 extremely minute that it would not be possible to recognize 

 them were it not for the presence of the centrosphere or the 

 astral rays by which they are surrounded. Free from these 

 structures, they would appear only as minute granules (micro- 

 somes), from which they are quite indistinguishable. 



After the extrusion of the second polar globule the sperm- 

 nucleus begins to grow rapidly. It becomes vesicular, devel- 

 ops a distinct membrane, and rises rapidly through the spirally 

 arranged cytoplasm toward the egg-nucleus, which lies at the 

 upper pole (PI. XI, Fig. 28). As the egg-nucleus and sperm- 

 nucleus enlarge, they keep pace with each other in develop- 

 ment, and by the time the sperm-nucleus has reached the upper 

 pole of the Qg% both nuclei have attained considerable size. 

 They are often temporarily prevented from coming directly in 

 contact with each other by the enormous reticulated centro- 

 sphere, which still persists in connection with the egg-nucleus. 



After the centrosphere has disappeared and the two nuclei 

 have attained their maximum growth, as shown in PL XII, 

 Fig. 32, they lie side by side at the upper pole of the ^g^. 

 No difference in size or structure can be detected ; they very 

 frequently, though not always, contain even the same number 

 of large nucleoli. There is, however, a constancy in the rela- 

 tive position of the two nuclei, by which they can often be rec- 

 ognized with perfect certainty. The egg-nucleus retains its 

 position at the periphery of the egg, where the Zwischen- 

 korper, that was formed between the second polar globule and 

 the %gg, still persists. Moreover, the sperm-nucleus, though 

 touching the egg-nucleus, generally lies a little deeper in the 



egg. 



The appearance of the egg of Limax agrestis at this stage 

 is precisely the same as that figured by Mark for the &gg of 

 Limax campestris, with the exception that the nuclear mem- 

 brane of Limax agrestis is always perfectly spherical in outline, 

 never amoeboid, as Mark had shown for Limax campestris. It 

 can easily be seen, by a comparison with the living Q.gg, that the 

 even outline of Limax agrestis is not the result of swelling 

 caused by the killing fluids, for the nucleus in the living Qgg 



