THE BREEDING SEASON 17 



hand, is a fresh-water fish which migrates to the sea for breeding, 

 and deposits its eggs in deep water (in spring and early summer ).'^ 



Jacobi^ showed that the migration of the eel is not determined 

 by the growth of the genital organs, for these do not begin to develop 

 until the fish have reached ^the sea. He concluded, therefore, that 

 eels need salt water before the genital organs can develop. Similarly, 

 Noel Paton ^ has pointed out that salmon, with their genitalia in all 

 stages of development, are ascending the rivers throughout the whole 

 year. 



Miescher,* too, has shown that salmon go practically without food 

 so long as they are in fresh water, being nourished by the large store 

 of material which they accumulated while they were in the sea. 

 This observation has been confirmed by Noel Paton. Miescher and 

 Paton have shown, further, that the gain in solid material (proteins, 

 etc.) by the genitalia,^ as the fish pass up the rivers, is met by a loss 

 in solid material in the muscles. This transference is not brought 

 aboilt by anything of the nature of a degeneration taking place in 

 the muscles ; but the latter appear simply to excrete or give out 

 the material which has been accumulated in them. It should be 

 noted, however, " that the gain of solids by the genitalia is small as 

 compared with the loss of solids by the muscle, that in fact the 

 greater part of the solids lost from the muscles are used up for 

 some other purpose than the building up of the genitalia." ^ Paton 

 concludes that the state of nutrition is the main factor determining 

 migration towards the river, and that, when the salmon has accumu- 

 lated a sufficiently large store of material, it returns to the rivers 

 which were its original habitat. It doe^s not seem possible, however, 

 to maintain that nutrition is a determining influence in the growth 

 of the genital, glands, since these are undeveloped when the fisft 

 begin to migrate and enter upon their period of starvation. 



Wiltshire ^ states that in some fishes, at the period of ovi-position, 

 the lips of the genital orifice swell and become congested. This 



1 Schmidt (J.), " The Breeding Habits of the Eel," Phil. Trans., B., vol. coxi., 

 1922. 



2 Jacobi, Die Aalfrage, Berlin, 1880. 



^ Paton, Fishery Board Report of Investigation on the Life History of the 

 Salmon, Glasgow, 1898. 



* Miescher, Histochemische und Physiologisclie Arbeiten, vol. ii., Leipzig, 

 1897. 



^ The gain in the genitalia is due largely to the formation of comparatively 

 simple proteins (protamines, histones, etc.). See Chapter VIII. 



" Paton, loc. cit. Milroy(" Chemical Changes in the Muscles of the Herring 

 during Reproductive Activity," Seventh International Congress of Physiolo- 

 gists, Heidelberg, 1907 ; abstract in Zent. f. Phys.,vol. xxi., 1907 ; and Biochem. 

 JoMr., vol. iii., 1908) has recently shown that similar changes take place in 

 the herring, in which, however, the starvation period is briefer. 



' Wiltshire, " The Comparative Physiology of Menstruation," Brit. Med. 

 Jour., 1883. 



