214 BULLETIN OF THE 



the female pronucleus presents a different appearance, one which in some 

 respects doubtless reproduces the natural condition more truly than the 

 acetic acid process, tiiough in other points it may be doubted if it does 

 not offer quite as much violence to nature as the latter. The pro- 

 nucleus, far from being wrinkled, presents a most delicate and even 

 outline, which seldom deviates from a continuous and often exquisite 

 curve. It often approaches a spherical form ; at other times it is ovoid, 

 or may even be pear-shaped (Figs. 68, 77, etc.). 



From a large number of comparisons, the conclusion seems reasonable 

 that, treated in this manner, the pronucleus, though very likely ap- 

 proaching quite nearly the form and proportions which it had in the 

 fresh condition, nevertheless has suffered an absolute reduction of size 

 much greater than in the other method of treatment, and somewhat 

 greater proportionate diminution than the vitellus. The same, too, is 

 doubtless true of the pronucleoli. 



No trace of a double contour can be found by the osmic acid method, 

 either for pronucleus or pronucleoli. The substance of the nucleoli, as 

 well as that of the pronucleus in which they are imbedded, appears per- 

 fectly homogeneous with the highest power used. (Hartn., obj. 9, oc. 4.) 



The nucleoli, as before, appear to vary somewhat in size, but are uni- 

 formly much more prominent than when treated with acetic acid. 

 They present a rounded form, but do not approach so closely that of 

 the sphere as in acetic acid specimens, and they show the same want of 

 regularity in arrangement that has already been noticed. 



In proportion to its service in making prominent the nuclear struc- 

 tures, osmic acid fails to be of value in making distinct the radiations 

 of the vitellus which characterize different stages in the development. 

 Some traces of the stellate figures may usually be made out, but they 

 are never present in that unequivocal boldness which belongs to acetic 

 acid preparations. 



The female pronucleus often lies in such close proximity to the sur- 

 face of the vitellus that the latter becomes involved in its extensive 

 foldings, and consequently shows corresponding wrinkles and depressions 

 (Fig. 73). In a more marked degree something of a similar nature has 

 taken place in a few of the specimens treated with osmic acid (Figs. 69, 

 75). In these cases, however, there is not a general wrinkling of the 

 pronucleus. The nearest portion of the vitelline surface appears as 

 though forced inward like a hollow plug, thus causing a corresponding 

 depression in the outer half of the pronucleus. 



Sometimes there is a similar plug-like projection froni the opposite or 



