DEVELOPMENT OF SPELERPES BILINEATUS 



183 



Half a minute earlier, a depression had appeared on the vertical CD 

 which in two and one-half minutes had extended some distance each 

 way. At 7 :07 the furrow in D had been completed by the union of the 

 furro^vs from I AD io 2 CD. Returning to quadrant A, we find that the 

 furrow in this blastomere had been moving more slowly. At 7:10, it 

 reached only four-fifths of the way towards 2 AB. Its further progress 

 was slow, the furrow being still incomplete at 7:25. On the vertical 

 1 BC, a depression appeared at 6 :52 that is, two minutes after that on 

 1 AD. This furrow extended into both adjoining quadrants at nearly 



1 1 a 



II d 



Figs. 10-12 



equal rates, if expressed in degrees, but actually more rapidly in B 

 since the arc is larger than in C. After 7 :02 progress of the furrow was 

 very rapid in B, extending at least 25° in the next minute-and-a-half. 

 In another minute, that is, at 7:04| it completed itself at the depres- 

 sion on AB which had remained inactive. Meanwhile, in C a depression 

 had appeared at 7:0H on 2 CD as above described. Two-and-a-half 

 minutes later it extended over about 9°. On the other side of the quad- 

 rant the furrow was progressing steadily. It was completed near 2 CD 

 at 7 : 10 by joining the furrow already present there. 



Egg 31 A, fig. 11. In C, a furrow started on 1 CD and progressed en- 

 tirely clockwise to 2 CB. In 5 a furrow started on 1 -45 and progressed 

 in the opposite direction to CB, where previously a depression had ap- 

 peared. In quadrants A and D there are curious shiftings and even 



