MUSEUM OF COMPAKATIVE ZOOLOGY. 585 



with those which the protoplasm can easily and instantaneously traverse with- 

 out being first obliged to dissolve them. Limiting layers, which have only a 

 single clear contour, while the other surface passes by insensible transitions 

 into the neighboring substance, may be given the name of ^^pellicule." 



Fol has also been impressed by the fact, that in the formation of the polar 

 globules the centre of the external aster reaches the surface of the vitellus, and 

 subsequently continues to occupy the most external portion of the globule until 

 the latter is almost detached. Without having observed the curvature of the 

 rays, he remarks that' the aster is of necessity incomplete, and thinks these 

 peculiarities should correspond to a difference (from ordinary cell division) in 

 the mechanism and forces of division. The amphiaster is in some way expelled, 

 pushed by a vis a tergo, instead of operating as two " centres d'appel." Since 

 they subserve no function for vitellus or embryo, and soon suffer disintegration, 

 he prefers the term globules or spherules to that of cells. Granting that there 

 are objections to the use of '-globules excretes," he claims the justice of the 

 name " corpuscules de rebut." They are small masses of a substance that has 

 become superfluous, or rather injurious, to the egg, and are for that reason 

 expelled. It is of little significance that this substance has, as germinative 

 vesicle and dot, played an important part in the growth of the ovule, or 

 that its mode of expulsion resembles the division of cells ; they are none the 

 less worn-out materials, and their constancy in the animal kingdom simply 

 tends to show that these substances have become injurious, — an obstacle to 

 "la fecondation intime" and to embryonic development. From all observa- 

 tions it appears that the expulsion of a part of the nucleus of the ovule may be 

 a condition indispensable to the fusion of the pronuclei. If that is the case, 

 one is naturally led to inquire if there are not in the germinative vesicle sub- 

 stances of different aJB&nities or polarities. The combination of these would 

 give a totality which would have no affinity, no attraction, for the male ele- 

 ment. In fact, the zoosperms do not advance toward the interior of the 

 vesicle so long as the latter remains intact. The eliminated substances should, 

 by this hypothesis, have a polarity of the same name as that of the zoosperm, 

 or the same chemical affinities. One could then .understand how it is that the 

 presence of a zoosperm in the vitellus hastens the elimination of the polar 

 globules. On the other hand, the penetration of a zoosperm into a polar 

 globule — a fact which has been once or twice observed — would remain inex- 

 plicable. The cause of the obstacle which it seems to offer to fecundation 

 would be seen in its size and inactivity. The expelled portion would be the 

 more passive, the female pronucleus the more active principle. 



Even if in fecundation it is evident that a zoosperm exercises an influence 

 upon the vitellus from which it is still separated by a relatively large space, the 

 mechanism of that action is not clear. The author sees only three hypotheses 

 which can accord with the facts. The zoosperm may be separated only in ap- 

 pearance ; there may be a continuity of sarcodic substance as soon as the 

 action is exerted. But as he has found no filament of sarcode extending from 

 the zoosperm toward the vitellus, and no change in the form of the body of 



