SECT. 7] OF EMBRYONIC DEVELOPMENT 999 



difference is associated with the difference between terrestrial and 

 aquatic forms. Generally speaking, aquatic embryos use a great 

 deal of protein during their ontogeny, but terrestrial ones are sparing 

 of it. 



This generalisation may, at any rate, be regarded as a legitimate 

 working hypothesis, and fits in with Gray's distinction between 

 aquatic and terrestrial embryos, in that the former can obtain water 

 for their tissues from their environment, while the latter cannot, so 

 that an apparatus has to be provided for storing the necessary water 

 in the egg, and supplying it at a steady rate to the embryo. The egg 

 of the trout, for instance, contains, like that of the chick, enough 

 solid to make one embryo, but, unlike that of the chick, not nearly 

 enough water. In the same way, the embryo of the trout, on the 

 view here propounded, need exercise no economy in the combustion 

 of protein, since it has an unlimited space into which to excrete the 

 resulting waste products, but the embryo of the chick, on the other 

 hand, has only a very limited means of disposing of such compounds, 

 and accordingly obtains its Ea. from substances that burn away com- 

 pletely to carbon dioxide and water. This subject will be more fully 

 discussed in Section 9-15. 



SUMMARY OF DEFINITIONS 



Ea (Tangl) = U (Rubner) = the " Entwicklungsarbeit," i.e. the chemical energy in that fraction of the raw 



materials of the egg, which is combusted by the embryo during its development. 

 REa (Tangl) = the Relative Ea, i.e. the Ea calculated for i gm. wet weight of embryo. 

 SEa (Tangl)=U( (Rubner) = the Specific Ea, i.e. the Ea calculated for i gm. dry weight of embryo (Tangl) 



or I kilo dry weight (Rubner). 

 OE = " Organisation-Energy," i.e. the energy stored in the embryo which, though appearing as calorific 



value of combusted wet tissues, would not result from the combustion of an unorganised mixture of 



its constituent chemical substances. 

 Wa (Tangl) = '* Wachstumsarbeit," i.e. that fraction of the Ea which is due to the function of Growth. 

 Na (Tangl)=" Neubildungsarbeit," i.e. that fraction of the Ea which is due to the function of Differen- 

 tiation. 

 Ua (Tangl)=" Umbildungsarbeit, i.e. that fraction of the Ea of insect metamorphosis which is due to the 



functions of Transformation and Rearrangement. 

 Ha=" Histolysearbeit," i.e. that fraction of the Ea of insect metamorphosis which is due to the function 



of Histolysis. 

 U (Terroine) = the amount of chemical energy stored in the raw materials of the egg. 

 Ui! (Terroine') = the amount of chemical energy in the unused raw materials at the end of development. 

 U' (Terroine) = the amount of chemical energy stored in the finished embryo. 

 W (Rubner) = C/' calculated for i kilo wet weight of embryo. 

 Wi (Rubner) = U' calculated for i kilo dry weight of embryo. 

 Uk (Terroine) = that fraction of the Ea u hich is due to basal metabolism. 

 AEE= Apparent Energetic Efficiency, i.e. the relation between the chemical energy in the material stored, 



and that in the material combusted during development, (U'/Ea). 

 REE = Real Energetic Efficiency, i.e. the relation between the chemical energy in the material stored and 



that in the material combusted during development for non-basal metabolism only (U'/Ea- Ui). 

 SEE= Synthetic Energetic Efficiency, i.e. the relation between the chemical energy furnished to the 



embryo by coupled reactions with one endothermic component, and that in the material combusted 



during development for non-basal metabolism only. 

 PEC = Plastic Efficiency Coefficient, i.e. the relation between the material {not the energy) stored in 



the embryo, and the material combusted by the embryo. 



64 



