338 BULLETIN OF THE 



tion, the radial figures disappear very rapidly, but the clear area in 

 which each nucleus is imbedded persists. 



The primary cleavage nucleus in Clepsine is found to He, according to 

 Whitman (78«),^ ''a little eccentrically toward the oral pole. The 

 nucleoplasm is more strongly colored in the centre around the pronu- 

 cleolar bodies than at the edges." There are usually three of these 

 " pronucleolar " bodies, which are " sharply outlined, but only slightly 

 stained with carmine." " The longer axis of the nucleus in this stage is 

 in every instance at right angles to the axis of the egg, whereas, at the 

 moment of union of the pronuclei, the longer axis was found parallel to 

 that of the egg, and a little later inclined about 45°." The " pronu- 

 cleoli " are several times larger than when the pronuclei meet. Between 

 the nucleus and the oral "polar ring" a line, more highly colored than 

 the rest of the yolk, is sometimes seen. This, from its position and di- 

 rection, Whitman interprets as the path taken by the female pronucleus 

 toward the male pronucleus. It occurs to me that it may be the same 

 structure which Fol has seen in the Pteropod egg. 



The nucleus elongates and then passes from a spindle- to the biscuit- 

 form. The " nucleoli," having dissolved, are no longer visible, but there 

 stretch through the centre of the biscuit-shaped figure "fine granular 

 lines, which together form a sort of spindle, the poles of which appear to 

 be near the centres of the polar areas." These interstellate lines are 

 more strongly expressed than the radial lines of the two polar areas, f 



At this time, says the author, the substance of the "polar rings" — 

 for an account of which the reader must be referred to the interesting 

 description given in the original paper — begins to plunge into the yolk, 

 and possibly contributes some elements to the nucleus which may stim- 

 ulate the molecular changes which result in the formation of the cleavage 

 amphiaster. 



Subsequently, there arises in each pole of the amphiaster " a central 

 area J which colors less with carmine than the surrounding nucleoplasm, 

 and in the edge of which the converging rays end." These central areas 

 undergo a modification from the round to the biconvex, and finally to 



* Compare also Whitman '78. 



t The eggs of Clepsine appear to be very unfavorable for the study of the nuclear 

 plate, for Whitman was unable to find any trace of it during the first segmentation. 



t This central area in a more advanced stage the author identifies with the cell 

 nucleus. His "nucleoli," therefore, correspond with what many observers consider 

 the still unfused elements of a nucleus, and his " nucleus " with what I have called 

 " area." A discussion of his views on this point will be found under Fecundation 

 (pp. 50i et seq.). 



