KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 239 
tion, into four loops—m, n, p, g—and this takes place, not in 
such a way that the four previous loops, a, b, c,d will be 
re-established, viz. that m = @ and n = 3, &c., but so that 
Mm. = 4.00, = 400; p = 4. cd, 9) = 15) cd. 
It is impossible by observation to distinguish whether the 
group ad contains the two male loops and cd the two female 
loops, or whether in each group one male is united with one 
female loop, so that a@ and ¢ are male and 6 and d are female. 
E. van Beneden thinks that the former is the more 
probable (ad = male, cd = female), since this is the case in 
the fertilized egg, with separate male and female pronuclei, 
and one cannot well believe that the daughter-cell will behave 
differently in this point from the mother-cell. As we see, 
according to this version, there is no question at all about a 
process of fusion, certainly not of the chromatin substance. 
This will only be distributed (vertheilt) equally to the two 
daughter-nuclei formed by the first segmentation. It is there- 
fore difficult to fix exactly the moment of true fertilization 
according to this view. H.van Beneden fixes it at the moment 
(see below) when the two pronuclei are complete. In 
his definition of fertilization, however, he goes somewhat 
further. Since the sperm-cell, after nipping off a part of its 
element, is somewhat different from before, E. van Beneden 
calls it no longer a cell, but a ‘‘male gonocyte;” similarly 
he terms the egg-cell, after the extrusion of the directive 
corpuscles and the perivitelline layers, a ‘ female gonocyte.” 
We quote these names in order that we may define impreg- 
nation in van Beneden’s own words :—“ Remplacement par 
certains éléments dérivés du gonocyte male des parties élim- 
inées par l’ceuf lors de la formation des globules polaires et des 
couches périvitellines” (1. ¢., xxiii, pp. 812 and 402). (“ The 
replacement of certain parts lost by the female gonocyte by 
parts derived from the male gonocyte.”) EE. van Beneden, 
therefore, finds in Ascaris megalocephala, although in 
another way, the same important process as Nussbaum saw in 
Leptodera nigrovenosa, i.e. the equal distribution of male 
and female nuclear elements to the first two daughter-nuclei, 
