36 



CELL-DIVISION AND GROWTH 



II. i 



plates were vertical, the eggs, therefore, compressed not, as before, 

 in, but at right angles to, the axis. 



The first furrow was meridional, and therefore vertical, and at 

 right angles to the plates. The second was latitudinal and hori- 

 zontal, and also at right angles to the plates. The furrows of 

 the third phase were parallel to the first, those of the fourth, in 

 the four upper animal cells, parallel to the plates. Born again 



FIG. 21. Segmentation of the Frog's egg under pressure. 

 The pressure is at right angles to the axis. 



A, view of the compressed egg. The pigmented animal portion is shaded. 



B, C, D, views of the egg from the animal pole after the first (1), the 

 second (2), and the third (3) divisions. 



E, F, G, views of the egg from the compressed side after the first (1), 

 the second (2), the third (3), and the fourth (4) divisions. The first 

 furrow may pass as (!') in E. 



(From Korschelt and Heider, after Born.) 



confirms this account (Fig. 21). The direction of the furrows of 

 the third phase is, however, variable ; it may be not parallel to the 

 first, but perpendicular to it. In this case it may be parallel to the 

 second, or so oblique to it as to become nearly parallel to the glass 

 plates. The direction of the fourth division depends on that of the 

 third, to which it is at right angles. It may, therefore, be either 

 oblique and nearly parallel to the plates, as described by Hertwig, 

 or parallel to the second furrow and perpendicular to the plates. 

 In a third series of experiments Hertwig placed the plates 



