MUSEUM OF COMPAKATIVE ZOOLOGY. 215 



deeper face of this pronucleus, which in turn impinges on a second 

 similar body. The origin and destiny of the latter will form the subject 

 of subsequent considerations. Thus, in optical section, one or both of 

 these pronuclei appear to have the shape of a crescent, with blunt 

 rounded horns. In these cases, caused, probably, by too prolonged or 

 vigoipus action of the acid, the contents of the pronucleus are altogether 

 homogeneous, and without any trace of nucleoli, notwithstanding the 

 size of the pronuclei. I am at a loss to explain this disappearance of the 

 pronucleoli. There is only one, not altogether satisfactory explanation 

 that has occun-ed to me. I have already stated my conviction that the 

 nucleus becomes more contracted by treatment with osniic acid than 

 when hardened in acetic acid. This diminution of size may best be 

 accounted for on the supposition that it suffers a loss of fluid compo- 

 nents, — becomes more concentrated, and compact. If such an as- 

 sumption is legitimate, it is at least possible that the above-described 

 condition may have been brought about by so prompt and considerable a 

 loss of nuclear fluid as to make the substance of the nucleus very compact 

 and refringent, — so refringent, in fact, as to leave no perceptible differ- 

 ence between the nucleoli and other parts of the substance of the nucleus. 

 Another possible assumption is, that the nucleoli were already dissolved 

 in preparation for the coming metamorphosis into a nuclear spindle. 



Ed. Van Beneden ('75, p. 698) has observed something which I am 

 inclined to think is very like what I have described, if not indeed 

 identical with it. I am not able to speak with the greatest certainty, 

 since the description referred to is not accompanied by figures, but I am 

 the more inclined to think the phenomena are identical, because Van 

 Beneden in this case also employed osmic acid. I shall recur to this 

 point again. 



II. Fecundation. 



In eggs examined soon after extrusion there are to be observed in the 

 vicinity of the vitellus a number of small ovoid bodies, which are at once 

 noticeable from their possessing considerably greater refractive power 

 than the surrounding albumen. (Fig. 49.) These bodies are of even 

 outhne, about 10 ^ long and 7 to 8/x wide. The greater number usually 

 lie near the vitellus, some apparently in contact with it, while numbers 

 are scattered irregularly in diff^erent |l|Pts of the albumen. Among 

 these may usually be found some which have a filamentous structure 

 protruding from one side. On further inspection it will appear that the 

 remaining portion is of the same nature, but from the closeness of the 



