BIOCHEMISTRY OF THE SEXUAL ORGANS 293 



which open into the oviduct, and it is interesting to note that the 

 substance secreted by these sexual glands is a mucoid substance very 

 similar to the pseudomucin found in cysts of the human ovary (see 

 Mammals, p. 276). 



The protein substances in the eggs of Invertebrates have not been 

 closely investigated. Vitellin is said to occur. 



The eggs of insects are comparatively rich in phosphorised fats. 

 By extraction with alcohol and ether, Dubois 1 isolated from locusts' 

 eggs a yellowish oil containing 1/92 per cent, phosphorus. 



Glycogen, purine bases, and cholesterin have been found in the 

 eggs of Bombyx. The changes which take place in the chemical 

 composition of these eggs, during incubation, have been investigated 

 by Tichomiroff. 2 



The following table shows that a considerable amount of purine 

 bases are formed during incubation. At the same time the fat and 

 glycogen diminish in amount, while the cholesterin remains practi- 

 cally unchanged and the phosphorised fats increase slightly in 

 amount. 



On the whole the changes are similar to those observed in hens' 

 eggs, except that glycogen is present in considerable quantities in 

 the egg and disappears during development as well as the fat, while 

 the phosphorised fats are apparently not utilised as a source of 

 chemical energy. The " energy of development " is very considerable, 

 and, calculated as a percentage of the chemical energy contained' in 

 the whole egg, is as great as in the case of the developing hen's egg. 3 



Other experiments on different insects 4 have confirmed the fact 

 that in these animals, as in birds, the main source of the energy 

 which is used up during development is fat. No nitrogen is lost, 



1 Dubois, "Sur 1'huile d'CEufs de la Sauterelle d'AIgerie (Acridium 

 pelerimim)" Compt. llend., vol. cxvi., 1893. 



2 Tichomiroff, loc. cit. 



' 3 Farkas, " Uber den Energieumsatz des Seidenspinners wahrend der 

 Entwicklung im Ei u. wahrend der Metamorphose," Pfliiqer's Arch., vol. xcviii., 

 1903. 



4 Weinland, Zeitsch. f. Biol., vol. xlvii., 1905 ; vol. xlviii., 1907 ; vol. li., 1908 ; 

 vol. Hi., 1909. Tangl, Pftiiger's Arch., vol. cxxx., 1909. 



