280 THE PHYSIOLOGY OF REPRODUCTION 



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 ichthuhn 

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

 from the blood. 



Together with the accumulation of fat in the muscles there 

 is a storing of a hpochrome, 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 yeUow pigment, 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 are re- 

 sponsible for the formation of the pink pigment. 



Invertd)rates 



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 TichomirofE ^ in the egg of 

 Bomhyx mori. He found it to be a protein body rich in sulphur, 

 and similar to the keratin substances 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.^ 



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," 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. 264). 



The protein substances in the eggs of Invertebrates have not 

 been closely investigated. ViteUin is said to occur. 



1 Tichomiroff, " Chemisohe Studien iiber die Entwicklang der Insekten- 

 eier," Zeitschr. f. phye. Chemie, vol. ix., 1 885. 



^ Von Furth, " Uber Glycoproteide niederer Tiere," Hofmeister'a Beitrdge, 

 vol. i., 1901, 



