62 CLEAVAGE II 



finding the value of the correlation coefficient (p). This 

 is, between the plane of symmetry and the sagittal plane 

 0451+ 0-035, between the first furrow and the sagittal plane 

 0-364 + 0-033, and between the plane of symmetry and the 

 first furrow 0-186 +0-043. This confirms the first result. We 

 shall return later on to the relation between the plane of 

 symmetry and the sagittal plane, but for the present it is 

 sufficient to say that a statistical inquiry does not bear out 

 Roux's assertion. 



In the second place Roux claimed to have produced from 

 one of the first two blastomeres a half -embryo. It must be 

 conceded that this sometimes occurs, but not always. Oscar 

 Hertwig, repeating the experiment, found that frequently the 

 living blastomere developed into much more than a half- 

 embryo, being apparently only impeded in its differentiation 

 by the presence of the inert mass of the other. Morgan 

 suggested that the capacity of the survivor to develop into 

 a whole depended on the position it occupied with regard to 

 the dead cell ; when the egg turned over so that the dead 

 blastomere lay underneath the living, the latter became a 

 whole, and it was indeed found by the same observer that if 

 the egg were turned upside down, the living blastomere gave 

 rise to a whole embryo. Precisely the same result is seen in 

 the experiment, due to Schulze, in which each of the two 

 blastomeres is made to develop totally and the egg to give 

 rise to a double monster, by merely turning the egg upside 

 down in the two-celled stage. The further analysis of this 

 experiment, by Wetzel, shows that under the influence of 

 gravity the contents of the blastomeres are redistributed, the 

 heavy yolk-granules sinking, the lighter cytoplasm rising, 

 until each blastomere has acquired a new polarity of its own ; 

 and in such a way that now the two polarities are opposed, 

 the two blastomeres like two eggs united by their vegetative 

 poles, and the two components of the double monster united 

 by the persistent yolk-plugs of their dorsal sides. There can 

 be little doubt that if it were possible to separate the two 

 blastomeres completely, each would give rise to an independent 

 larva, as happens in the Newt, where the separation can be 



