18 THE PHYSIOLOGY OF REPRODUCTION 



season. 1 In the other two Dipnoans, Lepidosiren of South America 

 and Protopterus of Africa, spawning occurs shortly after the 

 emergence of the fish from their summer sleep. Kerr, writing 

 of the former, says that the exact time for breeding varies 

 greatly from year to year in correlation with the extreme varia- 

 bility of the climate, the swamps, which the mud-fish inhabit, 

 sometimes remaining dry for prolonged periods. 2 



Many fishes migrate, before the commencement of the 

 breeding season, to localities suitable for the deposition of their 

 eggs. Thus, certain marine fishes like the salmon, the shad, 

 and the sturgeon ascend rivers for long distances before spawn- 

 ing ; others merely migrate to shallower water nearer shore. 

 The eel, on the other hand, is a fresh-water fish which migrates 

 to the sea for breeding, and deposits its eggs in deep water. 



Jacobi 3 showed that the migration of the eel is not deter- 

 mined 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 Pa ton 4 has pointed out that 

 salmon, with their genitalia in all stages of development, are 

 ascending the rivers throughout the whole year. 



Miescher, 5 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, &c.), by the genitalia, 6 as the fish pass 

 up the rivers, is met by a loss in solid material in the muscles. 

 This transference is not brought about 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 



1 Semon, In l/ie Australian Bush, London, 1899. 



* Kerr, " The External Features in the Development of Lepidosiren 

 paradoxa," Phil. Trans. B., vol. cxcii., 1900. 



3 Jacobi, Die Aalfrage, Berlin, 1880. 



4 Paton, Fishery Board Report of Jnrcxtiyations on the Life History of the 

 .W w ,m, Glasgow, 1898. 



Miescher, Hislochem^'sche und Physiologische Arbeiten, vol. ii., Leipzig, 

 1897. 



8 The gain in the genitalia is due largely to the formation of compara- 

 tively simple proteins (protaraines, histones, &c.). See Chapter VIII. 



