EMBRYOLOGY OF CLEPSINE. 239 



That this central area, which arises by a fusion of the two 

 pronuclei, does not disappear, nor even diminish in size, is cer- 

 tain, at least for the egg of Clepsine (figs. 66 — 72). The three 

 questionable corpuscles increase a little in size, but are at every 

 step small iu comparison with the central area of very fine 

 granular substance in which they are imbedded. Their fusion 

 does not take place till after the central area assumes the spindle 

 form. 



In their first and last stage (figs. 66, and 71) they are more 

 deeply stained with carmine than the nuclear substance of the 

 central area; and although well defined, possess no veritable 

 membrane. They are altogether similar to the nucleoli 

 of the germinal vesicle. In some of the intermediate stages, 

 particularly in that of fig. 67,/', they are exceptionally paler 

 than the nucleoplasm, and larger than in the following stages. 

 Their peri|)heral part is here quite highly coloured, and shades 

 off gradually into the pale central part. It is this stage, or 

 condition, more than any other, that bears a slight resemblance 

 to Butschli's figures. I believe the exceptional size and pale- 

 ness are here due to a variation in the action of the re-agents. 



The size, structure, chemical behaviour, and destiny of these 

 bodies favour the interpretation I have given them. On the 

 supposition that they are nuclei, what name should we give to 

 the substance which holds them in suspension, and which takes 

 the lead in the formation of the first cleavage-amphiaster ? 

 That this substance is nuclear is evident from reasons already 

 given; and since it maintains its individuality from beginning to 

 end, and always sustains the same relations to the small bodies 

 in its centre that are generally sustained between nucleus and 

 nucleoli, there seems to be no reason why it should not be 

 regarded as a nucleus. This view seems to me not only most in 

 harmony with the above facts, but also most consistent from a 

 theoretical standpoint. The uninuclear condition is the prime 

 characteristic of the cell. The pronucleus stage presents no 

 difficulty. The egg in this condition is not to be regarded as a 

 single cell with two nuclei, but as a pair of copnlating cells in 

 which like parts are in process of union. Two individualities 

 are blended in one, and the result is a single cell with a single 

 nucleus and one or more nucleoli. This view of the process of 

 fecundation has recently been emphasised by Strasburger 

 ( ^^-Ji—\. 



V4S3J09/' 



The formation of free nuclei, as in the eggs of some insects, 

 creates no real exception to the uninuclear character of the cell. 

 As soon as the germinal vesicle has divided into two parts, the 

 egg is no longer a single cell, but two cells, although their 



