BIOCHEMISTRY OF THE SEXUAL ORGANS 281 



lighten the work of synthesis laid upon the cells of the embryo. In 

 any case it is certain that the mother synthesises organic phosphorus 

 compounds for the offspring. In birds it has been shown l that the 

 blood of laying hens is much richer in phosphorised fats than that 

 of non-laying hens or of male birds. This indicates that these 

 substances are transported in the laying hen from their depots to the 

 egg, and this transport is associated with the disappearance of the 

 yellow colour from the body, especially the beak, legs, and anus, 

 the natural colour for the Leghorns and all American breeds. Thus, 

 birds with pale legs, beaks, and ani, are stated to have a high average 

 egg production and their blood is rich in fatty substances. The 

 converse is said to bold true for hens with distinctly yellow legs, 

 beaks, and parts surrounding the anus. 2 



The yellow pigmentation is due to a lutein which is associated 

 with the fatty substances both of the adult fowl and of the yolk. It 

 was isolated in crystalline form by Willstatter and Escher, 3 had the 

 composition C^HggOg, and found to be closely allied to, if not identical 

 with, the plant pigment xanthophyll. It is slightly different from 

 the lutein of the mammalian ovum. 



During incubation the vitellin disappears and the phosphorised 

 fats diminish, so that at the twentieth day their quantity is reduced 

 by one-half. 4 It is, of course, clear that the formation of nucleo- 

 proteins cannot account for this enormous consumption of phos- 

 phorised fats. Some of these substances reappear in the embryo. A 

 proportion of them contributes to the formation of bones, which 

 contain a considerable amount of inorganic phosphates ; part 

 reappears in the fnotal tissues as phosphorised fats, especially in 

 the nervous tissue, which is very rich in these substances. That 

 portion of the phosphorised fats which is transformed into inorganic 

 phosphates may at the same time fulfil another very important 

 function by the oxidation of the fat group in their molecule. It will 

 be shown below that the development of the embryo is intimately 

 associated with, and perhaps dependent upon, the transformation of 

 chemical energy into heat. This transformation is brought about by 



1 Lawrence and Riddle, " Sexual Differences in the Fat and Phosphorus of 

 the Blood of Fowls," .\<n<'i\ ./<'/: of /'/_//.>>>/., vol. xli., 1916. 



- Warner and Edniond, "Blood Fat in Domestic Fowls in Relation to Egg 

 Production," Jour. Bio/. (?/t<nn., vol. xxxi., 1917. 



3 Willstatter and Escher, " Uber das Lutein des Hiihnereidotters," Zeitsch. f. 

 physiol. ('/"-///. , vol. Ixxvi., 1912. 



4 Merconitzki, " Die quantitative!! Veranderungen des Lecithins im 

 enstehenden Organismus," /iNw/y/ M'/vAW,*, 1907, quoted from Biochemis<-ln* 

 Centmtblatt, vol. vi., 1907. Plimmer and Scott, "The Transformations in 

 the Phosphorus Compounds in the Hen's Egg during Development," Jour, of 

 WiitnioL, vol. xxxviii., 1909. Riddle, "Metabolism of the Yolk during Incuba- 

 tion," Amfi'. Jour, of /Vo/.nW., vol. xli., 1916 ; also Jn,i,\ <>f .\frphology, vol. xxii., 

 1911. 



