350 Blackman . — On the Fertilization , Alternation of 
differentiated vegetative cell and not from a specialized male cell or organ ; 
this will be discussed in the next section. 
A study of the cytological features of fertilization in various animals 
and plants shows clearly that actual fusion of nuclei is not a necessary part of 
fertilization as ordinarily understood. Although in Angiosperms the sexual 
nuclei fuse together before the egg develops further, yet in the Abietineae 
(Blackman, 6 ; Ferguson, 16), and in most animal eggs, development of the 
egg begins without the fusion of the nuclei, for the two begin to divide in- 
dependently and only meet together on the first division-spindle. Again, 
in the egg of Cyclops , we have cases in which the two nuclei can be 
distinguished for several cell-generations 1 . Not only was Rtickert (46) able 
to observe that in the first segmentation of the egg of Cyclops the two 
nuclei divide side by side in an association very little closer than that to be 
observed in the conjugate nuclei in the Uredineae ; but Hacker (17, 18) even 
observed double nuclei in the cells of the embryo up to the sixteen-celled 
stage (at what stage actual fusion took place was not determined). 
Again, in many cases of fertilization the fusion between the two nuclei 
is more apparent than real, for the chromatin and chromosomes derived 
from the male and female nuclei respectively have in a number of instances 
been traced as separate structures through several generations (eggs of 
Ascaris, Cyclops , &c., and the chromosomes in Pinus). Hacker (17) also 
believes that in the egg of Cyclops he has been able to trace the maternal 
and paternal chromatin as separate structures from the time of fertilization 
up to the formation of the next germ-cells. In fact all the cytological 
work of recent years tends to show that the chromosomes have a distinct 
‘ individuality/ and that the nuclei of the cells of the higher animals and 
the nuclei of the sporophytic cells of the higher plants are really dual in 
nature, there being no real mixing of the chromatin from the two sources 
until the time of chromosome-reduction 2 . 
A study of the varieties of fertilization in the higher animals and 
plants shows clearly that three morphological stages are to be observed in 
connexion with the complete sexual cycle — nuclear association within the 
1 Conklin (11) also in the egg of Crepidula was able to observe the double character of the 
nuclei at the telophase in every cleavage up to the twenty-four-cell stage, and in several cleavages up 
to the sixty-cell stage. 
2 See for example the work of Van Beneden, Boveri, Herla and Zoja, and of later years that of 
Sutton (52), and the observations on chromosome reduction of Montgomery (37, 38), Sutton (51), 
and Farmer and Moore (15). Sutton describes a very interesting case in which the chromosomes 
(twenty-three in number) in the spermatogonium of an insect ( Brachystola ) are not only of eleven 
different sizes, those of the same size being arranged in pairs, but the majority of them in the resting 
state are each contained in a separate diverticulum of the sacculated nucleus, the ‘ accessory chromo- 
some ’ lying in a separate closed vesicle and thus forming, virtually, a separate nucleus. 
The results obtained in certain hybrids in which the sexual cells are apparently ‘ pure ’ in 
relation to certain maternal characters also suggest that the nuclear material from the two sources 
remains distinct from the time of fertilization up to the formation of the germ-cells. 
