No. I.] POLYCHOERUS CAUDATUS. loi 



granules which are very characteristic of these ova I was struck 

 with their peculiar movements on the surface of the egg. To 

 quote the description written at the time : " Not infrequently 

 while examining the surface of a (living) ovum with an oil 

 immersion lens, I have seen one of these granules come up 

 from within the ovum and move across the field of vision. . . . 

 When the ovum is thus viewed it is clearly suggested that there 

 are wonderfully active forces at work within, for the surface 

 fairly scintillates with the movements of the protoplasm and 

 these pigment granules." Had I at that time known the size 

 of the spindle rays and the extent of the cytoplasmic network, 

 I should have felt less wonderment at the strange movements 

 of the pigment granules. These always find final lodgment in 

 a ring over the equatorial plate when the cytoplasmic rays are 

 least developed. While watching the surface of an ovum in the 

 two-cell stage I have seen one of the polar bodies lying close 

 inside the egg membrane bulge out the surface almost to the 

 bursting of the egg membrane, as if by pressure from below. 

 In the paper (lo) on the segmentation of this ovum the peculiar 

 distortions of the ovum in different stages are referred to and 

 figured. I cannot but believe that much of this is due to the 

 movements of cytoplasmic rays. 



At the stage shown in Fig. 36, when this remarkable cyto- 

 plasmic network was beginning to form, the centrospheres can 

 hardly be said to exist as a distinct structure, for when the 

 cytoplasmic network ceases the achromatic fibers begin. There 

 are, however, small clear spaces at the points from which the 

 achromatic fibers radiate. These spaces are the beginnings of 

 the centrospheres. As, however, the spindle grows, the cen- 

 trospheres enlarge very rapidly and become most conspicuous 

 structures. They at first are clear, colorless structures, but as 

 maturity approaches they become somewhat granular, with 

 occasional dark specks scattered here and there. Soon in 

 the center of each appears a clear, translucent spot in which 

 there is a small but distinct black or dark blue staining cen- 

 trosome. If the section is at all over-stained, the centreole 

 will stain as deeply as the centrosome, so that the whole struc- 

 ture, both centreole and centrosome, appears like an enormous 



