STUDIES OF FERTILIZATION 427 
granules introduced by the spermatozo6n represent a cytoplasmic 
element (whether concerned in inheritance or not), but of this we 
cannot be certain until their derivation is better known. 
The only characteristic thing about the cytoplasmic elements 
introduced by the spermatozoon is their great variability as to 
quantity and character in different animals. In Ascaris a very 
large quantity of cytoplasm containing characteristic plastosomes 
is introduced, as Meves has shown. In many, probably most, 
forms with flagellated spermatozoa, the entire spermatozo6n 
enters; in some echinids the tail is left without, and in Nereis 
both tail and middle piece fail to enter; and turning to plants, 
in phanerogams apparently nothing but the nucleus is eventually 
concerned. ‘There is nothing on the cytoplasmic side to corre- 
spond with the regularity of the nuclear phenomena in both ani- 
mals and plants. In such precise phenomena as those of inherit- 
ance a mechanism of equal precision is to be expected, and it 
must be admitted that on the cytoplasmic side no such mechan- 
ism has been discovered. Moreover, as the laws of inheritance 
are the same for animals and plants, a similar mechanism must 
exist for both, and such has been discovered only in the nuclei of 
the gametes. There is bad logic in the assumption that what- 
ever parts of the spermatozo6n enter the egg are necessarily 
concerned in the mechanism of transmission in inheritance, and 
the view that the cytoplasmic elements of the male gamete are 
concerned primarily in accessory functions of fertilization, such 
as locomotion and penetration, is still logically well founded. 
IV. THE FERTILIZING POWER OF PORTIONS OF THE SPERMATOZOON 
1. Introduction and methods 
In the second of these studies (F. R. Lillie, ’11) it was shown 
that the stimulus of the spermatozo6n in fertilization involves 
two phases: (1) an external phase, prior to entrance of the sper- 
matozo6n but after its attachment to the egg, in which certain 
cortical changes are induced, jelly is secreted by the egg and the 
mechanism of maturation of the ovum is released; and (2) an 
internal phase beginning after the entrance of the spermatozo6n, 
