EMBRYOLOGY OF BDELLODRILUS pot 
3b As 
Fig. 1 Two-cell stage from apical pole view. 
Fig. 2. Early three-cell stage from apical pole 
Fig. 3 Four-cell stage from apical pole view. 
Fig. 4 Four-cell stage from vegetal pole. 
a-b, median longitudinal plane of future adult; /-1, first cleavage plane; 2-2 
second cleavage plane; a, anterior; b, posterior; 7, right side; /, left side. 
the larger cell CD is posterior. The cleavage at first is very 
deep and the cells are rounded, but soon they begin to press 
against each other and flatten at their point of contact. Before 
the second cleavage begins the egg assumes its original ellipti- 
cal shape and the point of contact externally, between the two 
cells is represented by a mere line or shallow groove. No actual 
fusion of the two cells ever takes place; sections always show a 
distinct line of separation between them. 
The deutoplasm is equally distributed in both cells. The 
cytoplasm surrounding the nucleus contains very little yolk 
