Fertilization in Finns Strohus. 
449 
‘segmentation-nucleus.’ The sperm-nucleus is usually de- 
scribed as being more dense than the egg-nucleus at the 
time of their conjugation, and this is sometimes found to 
be the case in Pinus Sirodus ; as a rule, however, the con- 
jugation-nuclei differ in size only, as observed by Arnoldi 
(’00) in Cephalotaxus . 
Just before the sexual nuclei come into contact, the side 
of the egg-nucleus adjacent to the sperm-nucleus becomes 
slightly concave (Fig. 43). This concavity is doubtless 
formed under the influence of the approaching sperm-nucleus, 
and suggests the crater-like depression developed at an 
earlier period in the egg-nucleus of Cycas (Ikeno, ’98). As 
noted by Blackman, the sperm-nucleus does not penetrate 
the membrane of the egg-nucleus ; it lies in a pocket-like 
indentation formed in the side of the oosphere-nucleus, 
both nuclei then occupying the space originally filled by 
the egg-nucleus. The sperm-nucleus, when in contact with 
the nucleus of the egg, ordinarily assumes the form of 
a biconvex lens, but it may vary much in outline, pre- 
senting in some cases the figure of a crescent, and in others 
that of an ellipse. Occasionally it forms a deep, tongue-like 
depression in the nucleus of the oosphere (Figs. 41-50). 
The First Division following Fecundation. 
While the sexual nuclei lie in intimate contact, but still, to 
all appearances, perfectly distinct, certain changes in their 
structure indicate that each is in the early prophase of 
division. The chromatin condenses or collects in irregular 
granules about the periphery of the sperm-nucleus, while 
that of the egg-nucleus is deposited just beneath the sperm- 
nucleus. The remainder of each nucleus is filled with 
a granular, achromatic reticulum of great beauty, remind- 
ing one of delicate frost-work (Fig. 51). This condition 
suggests an early stage of fertilization in the sea-urchin as 
described by Wilson (’95). Wilson thinks that the sudden 
increase in linin may be only apparent, resulting from the 
