go FECUNDATION ; HETEROGAMETES. 
is formed in the wall (Fig. 31, B). Both cavity and slit are probably 
the result of a swelling of the wall on the side toward the lamella. 
The two edges of the slit roll upward and downward respectively, and 
in this way an opening is formed in the cell-wall. The next stage in 
development is marked by the contraction and rounding up of the 
protoplasm to form the egg, but the odgonium is still closed by the 
lamella. The nucleus lies in the upper end of the egg, and below it 
is the vacuole, which has become smaller. The nucleus resembles the 
nuclei of the vegetative cells, being relatively large with a large 
" A ' 1s y a ad 2 
[PA ete aa 
Fig. 31.—Fecundation in Gidogonium boscit.—(After Klebahn.) 
A, spermatozoid. 
B, young oégonium, showing origin of opening in the wall and lamella beneath. 
C, odgonium just after opening. 
D-G, upper portions of fecundated eggs, showing successive stages in fusion of nuclei. 
nucleolus (Fig. 31, C). The so-called receptive spot near the upper 
end of the egg is formed, according to Klebahn, by the withdrawal of 
the chloroplasts and not by the collecting of a special mass of cyto- 
plasm. Finally, the closing lamella disappears (probably by being 
partly dissolved in water), forming an opening for the entrance of the 
spermatozoids (Fig. 31, C, 4). No part of the plasmic contents of the 
egg is expelled on the opening of the odgonium, as has been claimed 
by some observers. That which is expelled, to judge from Klebahn’s 
