312 THE UNFERTILISED EGG AS A [pt. m 



Fremiet & Dragoiu found the dry material of the egg of the frog to 

 consist of 60 per cent, protein and only 14 per cent. fat. And this has 

 been the experience of all those who have analysed amphibian eggs. 

 Next to the hen's egg, the eggs of fishes have probably received 

 the most attention. The recorded analytical figures for fish eggs are 

 often deceptive, for many analyses have been made of salted fish 

 roes and egg-preparations such as caviar, but the greatest care has 

 been taken not to include in Table 30 results which might have been 

 vitiated in that way. The question is complicated by the fact that 

 analyses of the purified constituent egg-substances prepared from 

 preserved material may well be admitted into consideration, for, 

 except in certain cases, they would probably not undergo much 

 change during the process of preservation. As in the case of reptiles 

 and amphibia, the fish egg is characterised by its predominance of 

 proteins as the food of the growing embryo. It should be remembered 

 that, in all these comparisons, the yolk of the hen's egg is a more 

 proper standard of reference than the whole egg-contents, in which 

 case the differences become even more remarkable. This generalisa- 

 tion appears at all points; thus, the brook-trout, a fresh-water fish, 

 has 30 per cent, of protein and only 9 per cent, of fat, and the herring 

 has 26 per cent, as against 3 per cent. In Table 31 the protein/fat 

 ratios are collected together, and the difference emerges there with 

 great clearness. Though it is obvious that fishes vary considerably 

 among themselves as to the fat-content of their eggs, yet all of 

 them have more protein than fat. The only fishes in Table 31 

 which come near to being exceptions to this rule are the sturgeon 

 and the dogfish, both of which have an unusually high amount of 

 fat in their eggs (a fact which accounts for the superiority of Russian 

 caviar over other varieties, for the former is made chiefly from the 

 eggs of sturgeon) . Besides this general difference between the egg of 

 the bird and that of the fish, there are many others, but they concern 

 the chemistry of the individual components rather than the rough 

 constitution of the egg as a whole, and will, therefore, be dealt with 

 later on. If Table 31 be further studied, it will be seen that, as far as 

 can be known at present from the few analyses of crustacean and 

 cephalopod eggs, the superior proportion of protein over fat holds 

 good there also. Curiously enough, the only analysis we have for 

 a gastropod egg gives a picture more resembling the egg of the hen, 

 comparatively equal amounts of fat and protein being present. 



