24 
New Researches on the 
[January, 
After Hensen, in his treatise on Generation, has expounded 
the views of Hertwig on the nature of fecundation, he 
adds : — “ These are the views which are opening out ; their 
full theoretical elaboration has not yet taken place, partly 
because the behaviour of the nuclear threads or the original 
nuclear substance has not yet been examined, partly because 
the fa<5t that the head of the spermatozoid becomes a nucleus 
is still contested.” On the other hand, Flemming, after 
showing that the chromatine of the sperm-nucleus mixes 
with the female pronocleus, and contributes to increase the 
quantity of the chromatine of this latter element, admits 
that he does not know what becomes of the light halo sur- 
rounding the chromatine of the sperm-nucleus : — “ What 
becomes of the light halo which still surrounds the central 
corpuscles of the sperm-nucleus, when the the two nuclei 
meet together, I have not been able to ascertain.” 
I believe I have taken an additional step in the compre- 
hension of the phenomena of fecundation by showing : — 
1. That not merely the chromatic nucleus of the 
spermatozoon, but also the surrounding achromatic 
layer (perinuclear stratum, participates in the forma- 
tion of the male pronucleus. 
2. That the germinal vesicle furnishes the female pro- 
nucleus not only with chromatic elements, but also 
with an achromatic body. 
3. That the two pronuclei, without becoming intermixed, 
may attain by progressive maturation the constitution 
of ordinary nuclei. 
4. That in Ascaris megalocephala a single nucleus is not 
formed out of the two pronuclei, and that a seg- 
mentation-nucleus — in the sense which O. Hertwig 
gives to the word — does not exist. The essential 
point of fecundation does not lie in the union of the 
two nuclear elements, but in the formation of these 
elements in the female gonocyt. One of these nuclei 
is derived from the ovum, and the other from the 
spermatozoon. The nuclear elements expelled in the 
form of the polar elements are replaced by the male 
pronucleus, and as soon as two half nuclei (a male 
and a female) have been formed the process of fecund- 
ation is completed. 
In consequence of a series of transformations which the 
nuclear structure of each pronucleus undergoes, — trans- 
formations identical with those which take place in every 
nucleus undergoing division, — each pronucleus produces two 
