Fig. 1 . Cypraea carneola Linnaeus, a, Egg mass; h, capsule enlarged; c—n, cleavage stages; o , blas- 
tula stage; p, trochophore stage; q, gastrula stage. 
course of about Vi hour, nearly all the em- 
bryos in the two-cell stage had completely 
divided into four blastomeres of equal size, 
symmetrically arranged, and joined together 
by their inner surfaces. Like the first cleavage, 
this was vertical and at a right angle to the 
first. The nuclei of the blastomeres were 
grouped together about the animal pole. Fol- 
lowing each of the preceding cleavages, a 
contraction and rounding off of the blasto- 
meres occurred which resulted in their being 
joined at the cleavage planes by a compar- 
atively small area (Fig. 1 g, h) . 
By 11:00 P.M., another division had taken 
place in the horizontal plane and at right 
angle to the two preceding cleavages form- 
ing four micromeres and four macromeres 
(Fig. 1 h). 
At about the same time some embryos had 
undergone an additional division of the ma- 
cromeres, thus producing four more micro- 
meres, arranged outside of the others and 
located in the line of division between the 
macromeres. The cells of this division were 
