NGO. 2 VEEG OF AMIA AND IS *CLEAVAGE,. aees 
form acute or obtuse angles, as at the upper pole, or they may 
even terminate at points widely separated, as in Fig. 17. In 
some cases the grooves may not even reach the lower pole, but, 
diverging from a meridional plane, unite with the first groove 
at almost any point between the margin of the calotte and the 
lower pole. 
Third Cleavage. — By the time the second grooves have 
passed just beyond the margin of the calotte the third set of 
grooves appear. Ina majority of cases these are vertical, and 
occupy the positions shown in Figs. 5, 13, 15, 23, 24, and 25. 
They generally all depart from one or the other of the first two 
meridionals, thus giving rise to a distinctly bilateral appearance. 
In the egg followed (Fig. 5) the first of this set originated in 
the first meridional at 9.50. The second was formed in the 
adjacent quadrant, on the opposite side of the first meridional, 
at 9.51. The third appeared one minute later in the adjacent 
quadrant on the same side of the first meridional. The divi- 
sion of the remaining quadrant began at 9.54. The two furrows 
shown in Figs. 5, 6, and 7 later reached the lower pole, but the 
one first formed turned aside, running into the first meridional 
at some distance from the lower pole, while the remaining one 
united with the second meridional at about the level of the 
equator. 
It often occurs that one or more of the set depart from the 
first meridional, while the rest depart from the second, or w2ce 
versa (Figs. 13 and 24). Frequently one observes the condi- 
tion shown in Fig. 15, where all the grooves of this set pass in 
planes nearly parallel to the first or second meridional, giving 
rise to a bilateral form comparable with the 8-cell stage of the 
teleostean egg.* All these grooves may occasionally depart from 
a common point at the upper pole, and cut each quadrant of the 
calotte into two approximately equal portions, in which case 
the cleavage assumes a radial form such as has been described by 
Agassiz and Whitman ® in the pelagic fish egg. Rarely, if ever, 
do these grooves divide the quadrants equally at the lower pole. 
* Dean (No. 3, p. 425) speaks of this condition as if it were the general rule. 
6 Agassiz, A., and Whitman, C. O.: On the Development of Some Pelagic Fish 
Eggs. Proc. Amer. Acad. Arts and Sci., XX, pp- 23-75. 1884. 
