IV. i INITIAL STRUCTURE OF THE GERM 169 



consequently the 'qualitatively unlike' nuclei compelled to 

 assume an abnormal arrangement. Between horizontal plates 

 the first two furrows are, as normally, meridional and vertical 

 (Fig. 82) ; the third, however, is parallel to the first (instead of 

 latitudinal), and the fourth latitudinal (instead of meridional). 



Between vertical plates the first is meridional and at right 

 angles to the plates, the second latitudinal (horizontal) and near 

 the animal pole, instead of meridional, the third furrows are 

 parallel to the first, and the fourth meridional and at right 

 angles to the first in the four upper blastomeres. 



Now if nuclear division is a qualitative process, if, further, 

 the nuclei of the compressed egg are divided in the same way 

 in successive mitoses as are the nuclei of the normal egg (that is 

 to say if the first two nuclei are right and left, each of these 

 then divided into dorsal and ventral, and each of these again 

 into an ^anterior and a posterior), then as a result of com- 

 pression their distribution and arrangement must be altered (as 

 the figures show), parts which should be anterior will be lateral 

 or ventral, and vice versa, and a monster will be formed. Such 

 eggs give rise to normal embryos. Nuclear division is there- 

 fore not qualitative. From this conclusion there is only one 

 escape ; it may be argued that the orientation of the nuclei 

 remains unaltered when the direction of the spindles is changed 

 by the pressure, and that therefore the order of sequence of the 

 cell-divisions may be varied ad libitum, may be as ' anachronistic ' 

 as is pleased, without affecting in the least the mode of distribu- 

 tion of the, qualitatively unlike, parts, a contention, surely, which 

 would only be urged for the sake of supporting a thesis. 



O. Hertwig has also repeated Roux's experiment, killing, or 

 at least injuring, one of the first two blastomeres by a needle or 

 by means of electricity. The uninjured half segments to form 

 a mass of cells lying on the top of the dead blastomere, as 

 a blastoderm lies on the yolk of a meroblastic egg, and separated 

 from it by a segmentation cavity, although the latter may be 

 wholly within the living cells. This is Roux's Hemiblastula, 

 but in Hertwig' s case the dead cell lies below, a point, as we 

 shall see, of considerable importance. Later on a blastopore is 

 formed, but always, according to Hertwig, within the bounds of 



