SECT. 7] OF EMBRYONIC DEVELOPMENT 989 



6. Perhaps it is no coincidence that the respiratory quotient which 

 is found in the early cleavage stages of small marine eggs such as 

 those of the sea-urchin is in the near neighbourhood of unity. 

 Warburg's respiratory quotient of 0-9 for the first 24 hours of the 

 development of Arbacia pustulosa eggs and Shearer's respiratory 

 quotient of 0-95 for Echinus microtuberculatus are relevant here. \ higher 

 figure still was found by Faure-Fremiet, whose results with the eggs 

 of Sabellaria alveolata worked out at a respiratoiy quotient of i-o. As 

 indices of the nature of the combustions going on these figures have 

 to be accepted with caution, but it is natural to suppose that a stage 

 which lasts 5 days in the chick may last only a few hours in lower 

 animals which develop faster, so that the time to look for utilisation 

 of carbohydrate might be from fertilisation to the gastrula stage. 



7. Then Simon and Susanna Gage fed laying hens on Sudan III 

 and found that, although red yolks were laid, the embryos showed 

 no trace even of a pink colour until the i oth day of incubation. After 

 that time they became rapidly more coloured, until at hatching they 

 were quite red. One would suppose that, in order to be combusted, 

 fat would have to be absorbed into the embryo, and would take the 

 dye with it, as indeed did happen after the loth day. Murray's 

 estimations of fat storage in the embryonic body confirm this 

 (see Fig. 362), and point to an awakening of fat metabolism after the 

 mid-point of incubation. Then Tallarico and Remotti have brought 

 forward evidence showing that the lipase of the yolk increases markedly 

 in activity towards the end of incubation, while the latter worker 

 finds a precise correspondence between proteolytic activity of yolk 

 and intensity of protein combustion at the 8th day of development. 



8. The work of Riddle on the yolk and the yolk-sac is interesting 

 in this connection. From the 15th to the 20th day the yolk is practi- 

 cally the only supply of the chick, and his chemical study of it during 

 this period showed that there is a preferential absorption of fat. This 

 agrees exactly with the absorption curve. The neutral fat decreases 

 markedly in the yolk and the protein substances increase. 



9. The earliest statement that protein in the hen's e^gg must be a 

 source of energy is due to Sznerovna. She found a constant relation- 

 ship between the nitrogen in the embryo and the nitrogen in the 

 allantoic fluid, as 1 7 to i . 



10. Bialascewicz & Mincovna, working on the frog's egg, found 

 that up to hatching there had been practically no loss of fat, but 



