MUSEUM OF COMPARATIVE ZOOLOGY. 213 



Owing to its increase in size, one of its margins may even come into 

 closer proximity to the surface at an advanced stage than at an earlier 

 one. Its relation to the centre of the vitelline star now in course of 

 disappearance is hardly less interesting and important. It has already 

 been stated that the female pronucleus is not formed at the centre of 

 this .stellate figure. It might be added, there is strong ground for be- 

 lieving that it never comes to occupy such a relation to the radiating 

 fibres left in the vitellus after the detachment of the second polar globule. 

 Certainly, in advanced stages of its formation (Figs. 57, 59, 68), this 

 centre of radiation is distinctly outside the boundary of the pronucleus, 

 — to say nothing of the coincidence of their centres, — and often at a 

 considerable distance from it. It may be here remarked concerning the 

 last trace of the second archiamphiaster, that the rays of its internal 

 star fade away so gradually throughout their whole length that it is 

 often quite as difficult to distinguish them near their point of con- 

 vergence as at any other part of their course. Compare Fig. 59. 



The diameter of the female pronucleus may eventually attain one 

 fourth the diameter of the whole vitellus (Figs. 73, 74, 77), or even in 

 some cases a third of its diameter (Fig. 85). 



When treated with acetic acid its shape is extensively modified by 

 deep and numerous wrinkles and folds which have a very characteristic 

 appearance. The outlines are usually more or less concave outwardly, 

 as though caused by the thrusting outward of some angular contained 

 body ; yet the protruding points are not sharp, but close to the 

 apex become rounded, so that really there are no "cusps" formed by 

 adjacent curves, as one is inclined to think at first sight (Figs. 59, 80, 

 85, etc.). The outline becomes more irregular and wrinkled in advanced 

 stages of the nucleus. In this method of treatment, too, the outline 

 constantly appears double, and increases in distinctness in proportion 

 to the size of the nucleus. Within the latter, one distinguishes in 

 advanced nuclei a large number — up to fifty or sixty — of nearly 

 spherical bodies, the pronucleoli, which often exhibit double contour 

 lines. I have never seen one of these nucleolar bodies sufficiently dif- 

 ferent from the others in size, or behavior with reagents, to warrant the 

 distinction of a main and accessory nucleoli ; and only once (Fig, 52, 

 chromic acid preparation) have I seen anything like a nuclear reticulum.* 



When treated with osmic acid and subsequently stained in carmine, 



* P. S. In eggs of an undetermined species of Limax I have observed in both fe- 

 male and male pronuclei a single nucleolus of much greater size and more deeply 

 stained than the ojier nucleoli. Compare Figs. 80*, 80c, and explanations. 



