996 ENERGETICS AND ENERGY-SOURCES [pt. iii 



Table 126. Energy sources 



Animal 



ck (Callus domesticus) 

 g {Rana temporaria) 



ok trout {Savelinus fontinalis) 



nt Salamander {Cryptobranchus allegiieniensis) 



■ke {Tropidonotus natrix) ... ... ... Losses not known but combusted material considered to be 



(of at 

 non ... ... ... ■ ... — 26-8 lo-i — 13-0 4-2 



.worm {Bombyx mori) ... ... ... 1-98 ii'Si 8-08 0-74 9-2 4-37 



[ct [Pleuronectes platessa) ... ... ... — 0-213 0-0057 — 0-174 0-0204 



0-033 calculated 



playing an active part — would combust such and such substances at 

 such and such periods of its development because it would not have 

 at those times the capacity for combusting others. The molecular 

 orientations on its intracellular surfaces would differ at different 

 stages of its development, and its enzyme systems would vary pro- 

 foundly in activity. 



At present there is not enough evidence to allow us to make a final 

 choice between these views. The ovogenic hypothesis would commit 

 us to the belief that, if sufficient carbohydrate were present during 

 the protein and fat combustion periods, the utilisation of these latter 

 by the embryo would greatly diminish or disappear. On the embryo- 

 genie hypothesis we should have to believe that, howev^er much 

 carbohydrate were present during the protein period, the embryo 

 would continue to combust protein, for a close relationship would exist 

 between its source of energy and its stage of development. In favour 

 of the ovogenic hypothesis might be cited the case of the viviparous 

 embryo, which may possibly combust carbohydrate throughout its 

 development. But dangers beset any direct comparison between 

 embryos in ovo and in utero. Mammalian embryos have a continuous 

 perfusion system, non-mammalian embryos have not ; so that in one 

 case the proportion of embryo to nutriment does not alter, and in 

 the other case it does. Mammalian embryos can have all their com- 

 bustible material supplied to them in solution ; if the avian embryo 



I 



