No. I.] THE EGG OF UMAX AGRESTIS. 21^ 



is also perfectly spherical. Up to the time of the apposition 

 of the nuclei no asters are usually present in the eggs of Limax, 

 and the centrosomes, even if they be present, cannot be recog- 

 nized. When the asters first appear, they are almost always, 

 in closer connection with the sperm-nucleus than with the 

 egg-nucleus (PI. XII, Fig. 36), though sometimes they appear 

 directly between the two (PL XII, Fig. 33). There is no evi- 

 dence that a central spindle has been formed between the two 

 centrosomes when both asters are present. Sometimes one 

 aster appears before the other, as Mark has shown in Limax 

 campestris. The centrosomes look like homogeneous refractive 

 bodies, which stain very deeply with Heidenhain's haematoxy- 

 lin. When the asters first appear, there is no differentiation of 

 the center of the aster into a centrosphere. The astral rays 

 are at first few in number and relatively short, but very distinct. 

 As the asters enlarge, the rays increase in number and length, 

 reaching far out into the cytoplasm and sometimes coming into 

 contact with the periphery of the Qgg. After the formation of 

 the asters, the nuclear membrane is often slightly Battened on 

 the side toward the aster, but the rays do not seem to pene- 

 trate the nuclear membrane (PI. XII, Figs. 34 and 38). 



When the asters first appear, the chromatin in the nuclei is 

 in the form of small granules which show no regular arrange- 

 ment, but are scattered irregularly throughout the nuclei (PI. 

 XII, Figs. 33 and 34). Later, while the nuclear membrane 

 still persists, the chromatin granules become arranged in rows 

 along the nuclear filaments within the nucleus (PI. XII, Figs. 

 35 and 37) ; outside of the nuclear membrane, between the 

 nucleus and the centrosome, the astral rays appear to be directly 

 continuous with the nuclear filaments, and show distinct vari- 

 cosities. 



As the sperm-asters gradually give rise to the segmentation 

 spindle, and the nuclei come to lie side by side at the equator 

 of the spindle, as shown in PI. XII, Fig. 38, the sperm-nucleus 

 and the egg-nucleus can no longer be distinguished from each 

 other. The nuclei soon lose their membranes without forming 

 a segmentation nucleus, leaving the chromatin lying at the 

 equator of the spindle in two distinct masses. Later, when 



