454 



PRINCIPLES OF EMBRYOLOGY 



Lovtrup 1953) show that, in Amphibia at least, the succession is really 

 carbohydrate-fat-protein. Gregg and Ornstein (1953) found that certain 

 of the morphogenetic processes studied by Holtfreter in explants (cf. p. 

 444) were more sensitive to one group of enzyme inhibitors, others to 

 different ones, which suggests that they do not all derive their energy in 

 the same way. 



0-30 



0-20- 



10 - 



2 4 

 RKodnius 



FiGXJRE 20.22 



Changes in the rate of ox)''gen consumption during the development of 

 single eggs of the bug Rhodnius, at three different temperatures {D.C., time 

 of dorsal closure; scale at left and below). And the same for the anuran 

 Xenopus(B.G., beginning of gastrulation, iV.F., neural fold stage; scale above 

 and to right). (After Tuft 195 3.) 



A more direct approach to the problem of the energetics of morpho- 

 genesis would be to measure the actual forces which are exerted. In one 

 attempt to do this for amphibian gastrulation, a small steel ball was in- 

 serted among the cells of the invaginating mesoderm, and a bar magnet 

 placed nearby in such a position that the magnetic force on the ball 

 tended to prevent its movement. From a series of such measurements, 

 one can arrive at a rough figure for the maximum force which the 

 gastrulation movements can exert. This was found to be about 0*34 dynes 

 per mm.^ of the hemispherical surface of the ball (Waddington 1939/)). 



