Ch. X] 



MODIFICATION OF CLEAVAGE 



97 



vertical, i.e. at right angles to the glass plates. The second 

 furrows may cross the first furrow in the middle of its upper 

 and lower surfaces, so that four cells of equal size result ; or the 

 second furrows may sometimes pass to one side of the middle 

 point, so that two cells may be larger than the other two (Fig. 

 31, A). The last result may be due to a slight obliquity in the 

 position of the axis of the compressed egg. The third furroivs 

 (which normally are horizontal and at right angles to the pre- 



B 



Fig. 31.— A, B. Egg compressed axially (Diagram A, Fig. 30). A. Above ; B. below. 

 C, D. Egg compressed laterally (Diagram B, Fig. 30). C. One side ; D. other side. 



ceding furrows) are also vertical and at right angles to the 

 plates, and are generally parallel to the first furrow (Fig. 31, 

 A, B). The egg is now divided into eight cells, all lying in 

 one horizontal plane. In the black hemisphere the third fur- 

 rows abut against the second furrows (Fig. 31, A), but be- 

 low they as often run into the first furrows, as shown in the 



