226 BULLETIN OF THE 



At somewhat earlier stages (Figs. 73, 74, 79, 80), the nucleoli are 

 found to be very numerous. As many as sixty have been seen in a 

 single pronucleus, but generally about thirty are embraced in each of 

 the pronuclei. The variations in size are considerable in the same pro- 

 nucleus, and the average size is often noticeably different in those of 

 different eggs. 



Both pronuclei continue to exhibit a double contour (when treated with 

 acetic acid) even after the appearance of the asters of the cleavage sphere. 

 The outline is much wrinkled (Figs. 73, 74, 79, 80, 85). Usually at the 

 time of the first appearance of the new asters the pronuclei are close 

 together, and it is difficult, by reason of their foldings, to determine how 

 extensively the two bodies are in contact. In a few cases there could be 

 no doubt in the matter, as the nuclei were in contact at only a single 

 point, or not at all. The specimen shown in Fig. 79 must have been 

 hardened very early in the formation of the new amphiaster, as only one 

 of the asters is visible. In the more advanced stage represented in 

 Fig. 85, the extent of the contact is certainly much greater, and the dis- 

 tinctness of outline along the contiguous faces so much impaired as to 

 leave the impression that a fusion of nuclear substances has already 

 begun. In the vicinity of this plane of contact there are to be seen in 

 each of the pronuclei a few highly refractive granules much smaller than 

 the pronucleoli, and not arranged in any discoverable order. Aside from 

 these two sorts of contained structures, the contents of the pronuclei 

 remain, as before, homogeneous. 



The first cleavage amphiaster, in the earliest conditions seen, consists 

 either of a single stellar figure, or of two, quite limited in extent. The 

 rays are fine and approach the common centre so closely as to leave only 

 an exceedingly small area of homogeneous appearance ; in some cases, 

 indeed, it is impossible to make out such a definitely circumscribed por- 

 tion. The absence of a distinctly marked area is not confined, however, 

 to the early stages of the amphiaster. Eggs present in this respect 

 individual differences, so that in one the area may be seen with great 

 distinctness, and in another of the same age be indistinct ; even in the 

 same amphiaster one aster may show no line of demarcation about its 

 central area, while that of the other is sharply limited. The rays, 

 which at first are quite uniform in prominence, have been seen, at stages 

 a little later (Figs. 85, 82), to be differentiated in such a manner that 

 one side of the star is more conspicuous than the other. Whereas in the 

 earlier condition the central area appears spherical, in the more advanced 

 condition it is flattened in the direction of the line joining the halves of 



1 



