II. I 



CELL-DIVISION 



35 



towards the vegetative pole below, or may even remain parallel to 

 the first furrow throughout. The fourth furrows, Born says, are 

 parallel to the second. I have myself observed that this division 

 may be either parallel to the second, or latitudinal, even in different 



B ^-T 



FIG. 19. Segmentation of the Frog's egg under pressure. 



The compression is in the direction of the axis. 



A, view of the egg between horizontal plates; the animal part is 

 shaded. B, C, D, first (1), second (2), third (3), and fourth (4) divisions 

 as seen from the animal pole. (After Born, from Korschelt and Heider ) 



III 



FIG. 20. The first four divisions (/, //, ///, IV) in a Frog's egg com- 

 pressed between horizontal plates in the direction of the axis. The 

 third furrow is more or less meridional and vertical in three quadrants, 

 horizontal in the fourth, and this a smaller quadrant. The fourth furrow 

 is meridional in this quadrant, horizontal in the remaining three. 



quadrants of the same egg (Fig. 20). It will be observed that 

 the quadrant in which the third furrow is latitudinal is smaller 

 than the others. It is of great interest to observe the striking 

 similarity between the direction of the third and fourth furrows 

 in these eggs and the corresponding divisions in the Teleostean 

 egg where the blastodisc is compressed by the chorion. 



In the second series of experiments made by Hertwig the glass 



D 2, 



