484 BULLETIN OF THE 



Perez endeavors to explain Fol's observatiohs by supposing that the 

 head of the spermatozoon, being a httle higher or lower than the pro- 

 tuberance which occupied the focal plane, was " projected " upon the 

 latter, and was thus made invisible, while the cue remained distinct. (!) 

 This protuberance of the yolk, says the author, has nothing to do 

 with fecundation. It is simply an accident depending solely on an in- 

 terruption in the continuity of the mucous envelope, which thus forms 

 a point of least resistance at the surface of the egg, and therefore a cor- 

 responding deformation of the yolk. Such a penetration is, moreover, 

 an anatomical impossibility, on account of the existence of a vitelline 

 membrane from a very early stage of egg development. 



FoL ('77^) communicates interesting results concerning abnormal 

 fecundation in the starfish, and deduces from them important conclu- 

 sions. If the spermatozoa are brought into contact with eggs before the 

 formation of the first polar globule, the vitelline membrane is formed 

 and detached only very slowly around the point where the first sperma- 

 tozoon penetrates, and extends over only a fraction of the surface, so 

 that other spermatozoa continue to effect an entrance, until finally the 

 joint result is a continuous envelope. The extent and rapidity with 

 which this membrane is formed are proportional to the nearness with 

 which the normal conditions are approached. The deportment of the 

 individual spermatozoa is the same as in normal cases. The nearest 

 male pronucleus unites with the female pronucleus, which becomes at 

 once the centre of a system of radial filaments. The resulting " noyau 

 combine " unites with a second, or even a third, male pronucleus. At 

 other times the female pronucleus, at the moment of its formation, sepa- 

 rates into two or three fragments, which unite with as many male pro- 

 nuclei. The male asters never unite with each other ; they appear to 

 repel each other, and to be attracted by the female pronucleus up to the 

 time when the latter has been neutralized by union with two or three 

 male pronuclei. When there are numerous male centres, the vitellus in 

 its segmentation forms at once a like number of rounded elevations, — 

 each with a male aster in its centre, — which become little spheres and 

 continue to divide dichotomously. Thus the cleavage process is irregu- 

 lar, and there results an irregular blastosphere and a monstrous larva. 



When the male pronuclei are limited in number and the female pro- 

 nucleus is divided into two or three, the latter remain distinct. At the 

 moment of cleavage each is converted into an amphiaster and the vitel- 

 lus is divided at once into four or six spherules. Cleavage was never 

 observed when the single nucleus resulted from the union of several 



