292 THE PHYSIOLOGY OF REPRODUCTION 



muscle during that period is a loss of fat, with which the muscles 

 are loaded when the salmon leaves the sea. The protein constituents 

 if the muscle also diminish, hut not to the same extent as the fat. 

 There is, further, a disappearance of the inorganic phosphates of the 

 muscle. From these suhstances the ovaries build up their essential 

 constituents the phosphoprotein ichthulin and the phosphorised 

 fata. The source of the choline which is contained in the .phos- 

 phorised fats is not yet clear. This formation by the ovaries of 

 phosphorised fats out of fats and inorganic phosphates points to the 

 ini]M>rtant function which these organic phosphorus compounds have 

 to fulfil in the developing organism (see above). 



Not all the fat which disappears from the muscles reappears in 

 the ovaries as phosphorised fats. A portion of it serves as a source 

 of energy for the animal. The same applies to part of the protein 

 of the muscle. 



The iron contained in organic combination in the ichthulin of 

 the ova is derived partly from the muscle and partly also from the 

 blood. 



Associated with the accumulation of fat in the muscles there is a 

 stming of a lipochrome or lutein, the characteristic pink pigment of 

 the flesh of the salmon. During its sojourn in the river this pigment 

 disappears in part from the muscles and is transferred with the fat 

 to the ova. This pink pigment is probably formed from another 

 yellow piginent, which is also present in the salmon, and which is 

 widely distributed in the animal kingdom, always closely associated 

 with fat. It is possible that the ingestion and deposition of fat 

 containing this yellow pigment is responsible for the formation of 

 the pink pigment. 



In rcrtebrates 



The chemical composition of the eggs of Invertebrates does not 

 appear to be essentially different from that of the Vertebrate eggs. 

 The covering of the egg, which is often stated to be chitin, has been 

 investigated by TichomirofF 1 in the egg of Bonibyx mori. He found 

 it to be a protein body rich in sulphur, and similar to the keratin 

 sul istances of which the membrane of the hen's egg is composed. 

 The covering of the eggs of a cephalopod the cuttlefish was 

 investigated by von Fiirth. 2 



These eggs are united by their capsules, which are often coloured 

 black by pigment, and form what are popularly known as " sea-grapes." 

 The covering or capsule is secreted by two "nidamental glands," 



1 Tichoui in.tr, "ChemUche Studien iiber die Entwicklung der Insekteneier " 

 JUltMA./ /'//.</./-./. f%m., vol. ix., 1885. 



1 Von Furth, " Uber Glycoproteide niederer Tiere ," HofmeisteSs Beitraae, 

 vol. i., 1901. ^ 



