350 EYCLESHYMER. [Vol. X. 



and Dumas ('24). Again, the furrows may not arise in the same 

 locality, in which case the two are united by the short piece 

 of the first furrow intervening, to which the designation "cross- 

 furrow" has been applied. 



These furrows do not always begin at the same time ; one 

 may precede the other by a considerable interval. At the 

 vegetative pole many variations are likewise found ; often the 

 two join to form a continuous line running at right angles to 

 the first, again forming acute and obtuse angles. 



In the axial line where the four quadrants of the Q%g join, 

 along a region just above the center of the Qgg, sections show 

 an open space, which is the first indication of the segmentation 

 cavity. 



Third cleavage. — In i hr. 45 min. after the appearance of 

 the second set of furrows, and even before they have reached 

 their destination, there are indications of the first horizontal 

 division at or near the limits of the dark hemisphere (Fig. 7). 

 In the particular ^g^ from which the diagrams are made, quad- 

 rant b (Fig. 14) was the first to divide, the furrow started from 

 the second vertical (indicated in the figure by a dotted line) 

 and progressed from left to right. In 4 min. it reached the 

 first vertical. 



The next division occurred in the adjacent cell d a few 

 moments later, extended in the same direction, and reached its 

 destination in about the same time ; 3 min. later a third furrow, 

 starting from the first vertical, appeared in cell a, and pro- 

 gressed in the same direction as the two preceding. Its rate 

 was more rapid, however, reaching the point at which the first 

 terminated in less than 2 min. Before this furrow was com- 

 plete, cell c divided from right to left. The entire time occu- 

 pied in the formation of this set of furrows is extremely brief 

 as compared with the preceding cleavage. 



In point of origin and direction of progress many variations 

 occur. They may depart from a common point at either the 

 first or second vertical. In many cases they appear succes- 

 sively in the different quadrants, following the direction of 

 the hands of a clock, again passing in precisely the opposite 

 direction. 



