No. 2.] OOKINESIS. 235 



the male pronucleus reaches the centre of the egg before the 

 female pronucleus is formed, as shown in the following state- 

 ment: " Le spermatozoide, modifie comme je I'ai expose plus 

 haut, occupe pendant toute la periode qui se termine par I'cx- 

 pulsion du second globule polaire et la liberation de la seconde 

 couche perivitelline le centre geometriqiie de I'oeuf " (p. 489). 

 Morever, Van Benedcn states that, in order to meet the male 

 pronucleus, the female pronucleus traverses the greater distance, 

 and hence, by inference, moves the more rapidly: " Pour se 

 rejoindre a son congenere le pronucleus femeJle, qui prend tou- 

 jours naissance au voisinage du p6le superieur de I'oeuf, parcourt 

 un chemin beaucoup plus long que le pronucleus male; celui-ci 

 se deplace relativement peu" (p. 524). 



In saying that the female pronucleus makes a longer journey 

 than the male pronucleus, the author evidently wholly ignores 

 the distance previously traversed by the latter in reaching its 

 central position.^ 



We find, then, three facts, which can be said to furnish indis- 

 putable evidence of attraction between the pronuclei. These 

 are : — 



1. The curved ^2i\h of the male pronucleus in the amphibian 



2. The meeting of the pronuclei before reaching the centre of 

 equilibrium. 



3. The centrifugal movement of the earlier pronucleus to 

 meet the later formed pronucleus. 



That this attraction acts only at comparatively short dis- 

 tances, and not at all distances which may separate the places 

 of origin of the pronuclei, is demonstrated by the following very 

 interesting observation of Fol's (6, p. 106) : "A mesure que 

 Taster male s'avance dans le vitellus, ses rayons deviennent 

 toujours plus longs et plus accentues ; sa liaison avec son point 

 d'origine a la surface du vitellus se perd. Sa direction, d'abord 



* It will probably occur to any one tolerably familiar with Van Beneden's paper, 

 that he holds that the pronuclei are contemporaneous in origin, while the validity of 

 my explanation rests upon a contrary assumption. The contradiction is, however 

 only apparent, not real ; for it is one of words rather than facts. The difference 

 is accounted for by the fact that Van Beneden maintains that the spermatozoon 

 undergoes a sort of maturation after penetrating the ovum, and that the changes 

 through which it becomes a proper pronucleus take place only after it has 

 reached the centre, simultaneously with the formation of the female pronucleus. 



