SECT. 3] AND ORGANISATION 543 



Driesch, and many other workers have observed these polynuclear 

 undifferentiated masses in other embryos with abnormal temperatures. 

 Even in bacteria growth in size can take place without cleavage, 

 according to Henrici, and the work on the endocrine control of 

 amphibian metamorphosis affords other instances of continuous 

 growth without differentiation. 



The most remarkable case of this, perhaps, is contained in the 

 work of Hoadley, who transplanted embryonic organs of the chick 

 on to the chorio-allantoic membrane and allowed them to develop 

 there until they had reached a degree of differentiation equivalent 

 to that of the controls. Then by making and weighing wax models 

 he ascertained the relative weights, and always found that the con- 

 trols were much heavier. But there was a direct relation with age, 

 for the younger the transplant at the time of transplantation the 

 smaller the eventual (fully-differentiated) organ, thus: 



„ 40 0-00075 



Another instance of the independence of growth-rate and differentia- 

 tion-rate is afforded by the genetic races of rabbits which differ 

 considerably in size. At birth the large-sized race is twice as heavy 

 as the small-sized race, and at the adult stage, three times as heavy. 

 In 1928 Painter observed that equally differentiated 12-day embryos 

 showed the characteristic weight-differences and thought that the 

 effect might be of endocrine origin, but Castle & Gregory were later 

 able to trace it back as far as the morula stage. The large-sized race 

 showed consistently more rapid cell-multiplication and size increase 

 in the embryonic period with unaltered differentiation-rate. There 

 is no difference in egg-size: but the large-sized race grows more 



^ ^ ' ' Embryo age Average no. of Diameter of 



in hours blastomeres blastodermic vesicle 



Large-sized race ... ... 48 21*75 — 



Small-sized race ... ... 48 14-00 — 



Large-sized race ... ... 100 — 31*4 



Small-sized race ... ... 100 — 16-3 



Another good instance of this dissociation of the fundamental 



