SECT. 7] OF EMBRYONIC DEVELOPMENT 955 



egg was provided to the extent of 63-4 per cent, by fat combustion 

 and 36-6 per cent, by the combustion of some other substance 

 or substances, of which protein was probably the most important, 

 though, from Tichomirov's earher work, some carbohydrate was 

 probably also utilised. Table 119 illustrates these facts. By run- 

 ning one series of larvae right through after hatching during a 

 hunger period of some days, Farkas was able to get some idea of 

 the energy relationships during this post-hatching period, during 

 which the remains of the yolk are used. As Table 120 shows. 



Dry weight 



Fat 



Energy 



the values for the post-embryonic period are all lower than those 

 for the time before hatching. Comparison of these results with the 

 analytical figures indicated that substances of lower energy-content 

 than either fat or protein were combusted for energy during this 

 period. 



Tangl & Farkas next published a joint paper on the development 

 of the trout embryo They found that r egg (presumably of Salmo 

 fario) weighed 88-2 mgm., and contained 193 cal. energy. The 

 specific energy-content (i.e. per i gm. dry weight) was 6453 cal. 

 For 5 1 8 eggs the energy-content before development was 99 • 85 Cal. , and 

 after it 96-39 Cal., showing a loss of 3-46 Cal. during the process, or for 

 one egg 6-68 cal. Neither nitrogen nor fat diminished — ^in fact, the latter 

 rose by 37 per cent. — a circumstance which led Tangl & Farkas, after 

 various experiments, to the suggestion that urea and uric acid were 

 acting as sources of energy. This remarkable assumption has since 

 turned out to be unnecessary, and will be discussed later (see p. 1 1 18). 

 Tangl & Farkas could not calculate the R.Ea. and the S.Ea. for 

 they were unable to ascertain the weights of the embryos at the 

 various stages. 



