MUSEUM OF COMPARATIVE ZOOLOGY. 457 



ity of committing the same mistake as the earlier writers, who con- 

 cluded that the germinative vesicle divided because they saw a nuclear 

 structure (which we now know is not the germinative vesicle) undergo 

 such changes as are here reported. The observations of stellate figures 

 on living eggs are too numerous to allow the acceptance of his con- 

 clusion that they are due to the use of reagents. The figures given by 

 Galeb are interesting in several particulars. His Fig. 3 (PI. XXII.) 

 probably shows the pronuclei, which Biitschli figured four or five years 

 ago in a similar situation. Whether it is the germinative vesicle or the 

 female pronucleus which is shown in Fig. 1, it is noticeable that the 

 structure is not in such a position as to warrant the supposition that 

 the polar globules are produced at the equator of the Qgg, where the 

 first cleavage plane occurs. The position of the globule after its libera- 

 tion would, of course, be of comparatively little value in determining 

 this point, because of the possibility of its passively being made to 

 occupy a position different from that which it had when first produced ; 

 in the case of the female pronucleus or germinative vesicle, however, 

 such a displacement could not be assumed. If future observations 

 directed to settling this point — the mutual relation of the first cleavage 

 plane and the polar globule at the time of its formation — shall show 

 that in some nematodes the globule is formed at the pole of the Qgg, and 

 that the segmentation plane passes through the equator, it will be nec- 

 essary to seek some explanation of this variation from what now seems 

 to be a very general law. The possibility of a rotation of the yolk after 

 the formation of the polar globules, so that the pole of the yolk comes 

 to occupy the equator of its shell, is not to be lost sight of in this 

 connection. 



Balfour ('78"), after giving a concise account of recent progress in 

 the study of the maturation of the ovum, states some conclusions which 

 he thinks already warranted by the observations (pp. 120-124). The 

 peculiar changes which the germinative vesicle undergoes at the time 

 of maturation are, in part at least, of a retrogressive character. The 

 budding of the polar cells is entirely independent of impregnation. He 

 says further, "I would suggest that in the formation of the polar cells 

 part of the constituents of the germinal vesicle which are requisite for 

 its functions as a complete and independent nucleus* are removed to make 

 room for the supply of the necessary parts to it again by the spermatic 

 nucleus." From the probable absence of polar cells in cases where par- 

 thenogenesis is most common, he is led to suggest further, " that a more 



* The original is not Italicized. 



