156 PROCEEDINGS OF THE ACADEMY OF [1897. 



All the eggs in the chain are never found to be in the same stage 

 of segmentation. The following will show the typical arrangement : 

 in a chain of 22 eggs, numbers 13,18 aud 20 were unsegmented; 2, 

 5, 6, 7, 9, 12 and 16 were 2-celled ; 14, 3 and 4 were 3-celled ; 1, 8, 

 15 and 22 were 4-celled ; 10 was 5-celled. The observation was 

 made at 2 P. M. ; by 3 P. M. the successive changes had taken 

 place in all these eggs with the exception of 13, 18, 20, 10 and 14, 

 all of which were probably dead. 



The segmentation in S. borealis is unequal. The first cleavage 

 plane is equatorial, and takes place as the following will serve to il- 

 lustrate : 



11.00 A. M., egg unsegmented. 

 11.05 A. M., slight notch visible. 



11.30 A. M., segmentation plane visible for one-half the circum- 

 ference of the egg ; polar globules jiresent. 

 12 M., faint, but complete segmentation plane, 2-celled stage. 

 1 P. M., marked segmentation plane, resting period. 



The egg having passed through the above described changes is 

 now divided into two unequal portions, the smaller of which is ellip- 

 soidal, giving the whole egg a somewhat dumb-bell shaped appear- 

 ance. The capsule is distinct, but more closely approximated to the 

 surface of the egg than in the preceding stage. There is no marked 

 change in color, the lower larger cell is somewhat darker than the 

 upper. 



In the 3-celled stage the division plane passes upward through 

 the smaller of the two cells already formed ; this stage then consists 

 of one large and two smaller unequal cells. 



By continuation of the division plane of the last stage the lower 

 and larger cell becomes divided into two unequal cells. This sec- 

 ond segmentation plane is at right angles to the first or segmentation 

 plane of the 2-celled stage. But by their peculiar intersection with 

 each other, neither plane is any longer a continuous circle; the 

 points of intersection are marked by z-shaped lines. The lower left 

 cell is darker than the others, containing the most yolk. In seg- 

 mentation of these eggs the first furrow or segmentation plane al- 

 ways bends to the right, the second bends to the left. 



The next division takes place in a plane at right angles to the 

 last. The first cell to be divided is the smallest of the four already 

 existing cells ; the polar globules take their position at the right 

 hand side of this small cell. The general shape of the egg becomes 

 modified somewhat at this stage. It is now irregularly spheroidal. 



