ii88 FAT METABOLISM [pt. m 



from the table, for terrestrial eggs store the greatest amount of fat, 

 so that 20 per cent, of the fat in the hen's egg is a good deal more 

 proportionately to the embryonic weight than 20 per cent, of the fat 

 in the sea-urchin's egg. But any direct comparison between the 

 terrestrial or aquatic environment and the amount of fat stored in 

 the egg is not possible, for, as Table 31 (in which the fat/protein 

 ratios of many eggs are given) shows, there is no strict correlation. 

 The terrestrial sauropsid egg contains much more fat than any of 

 the others, relatively to the protein, but the insect egg, which is also 

 terrestrial, contains very httle (e.g. silkworm and lackey moth). In 

 other words, the correlation between environment and material used 

 as energy source does not appear until one knows the exact amount of 

 material combusted during development, and expresses that in terms 

 either of the amount of it originally present, or of the total material 

 combusted. 



Now we have seen that, in six separate instances, an absolute 

 increase in fatty acids has been observed during development, one 

 of the animals in question being a urodele amphibian, two being 

 teleostean fishes, and one a pulmonate gastropod (all aquatic em- 

 bryos). It is likely, in view of the discussion on p. 350 about the oil 

 drops in fish eggs, etc., that this list would be much prolonged if 

 more investigations were made of their chemical embryology. 



What is the nature of this fat synthesis? Tangl & Farkas, who 

 were the first in recent times to establish it experimentally, thought 

 that the trout egg contained "glycoproteins" which were broken 

 down to carbon dioxide and water, but which also went to form 

 glycogen and fat. They believed, in fact, in a predominance of pro- 

 tein metabolism and in a formation of fat from protein, the waste 

 nitrogen being retained in the egg in the form of urea, and liberated 

 at hatching to the exterior. Tangl & Farkas, however, made no 

 attempt to demonstrate the presence of urea. Then Gortner, in his 

 studies on the protein metabolism of the trout and salamander egg, 

 concluded that this could not be the case, as no urea or uric acid 

 was to be found in the eggs at the time of hatching. Unfortunately, 

 he neither identified the urea and uric acid specifically nor brought 

 forward evidence in disproof of their presence by the use of appro- 

 priate tests. In view of the importance of the subject, it would be 

 highly desirable for a new investigation to be made of the protein 

 metabolism of the trout egg. The fact of the matter is that neither 



