Distrihution of Marine Animals. 123 



the Pacific. Two families (Lycodidse and Gadida^) inhabit 

 the Arctic and Antarctic seas only, though one species of the 

 latter (Gadida^) exists in the Indian Ocean. One extensive 

 genus {Diagrninma, family Pristipomatidfe) is confined to 

 the Pacific, with the exception of a single species in the 

 Mediterranean. One family (Notacanthi) has representatives 

 in Greenland, the Mediterranean, and West Australia. 

 Lastly, the single representative of the family Lophotidse is 

 found only in Japan and the Mediterranean. Similar results 

 follow in considering the classification of Prof. Palacky, of 

 Prao- *. Further and more minute investigation of the 

 several areas may reduce the number of these anomalies ; but 

 it is difficult to unravel the tangled web of the distribution of 

 fishes. 



In glancing at the families most widely distributed it is 

 found that a considerable proportion of them have pelagic 

 eggs, but others, such as the blennies, gobies, and pipe-fishes, 

 have demersal eggs, and the fishes themselves are not noted 

 for switt progression or nomad habits. From the fact that 

 some cosmopolitan forms, such as the Clupeoids, have both 

 pelagic and demersal eggs within the limits of the family, 

 this condition would not seem to be the chief factor asso- 

 ciated with their distribution. Some families have represen- 

 tatives on the shores of Britain, Chili, and Kamschatka, 

 whilst others frequent the open sea in all parts of the world. 

 Fishes, like the wrasses, which occur on the European and 

 American shores and extend to Japan and New Zealand, 

 increase the complexity of the problem. The facts of distri- 

 bution, indeed, may be associated with the origin of the fishes 

 from pre-existing forms, for the families could scarcely have 

 arisen as the result of variation since the land and water 

 had their present conformation. Again, the occurrence of 

 isolated species or genera at points widely distant from other 

 members of the family indicates, amongst other things, that 

 the production of species by variation is in some cases very 

 slow. 



The comparatively recent origin of the Teleosteans has 

 made no noteworthy limitation in the distribution of the 

 families, in contrast with the much older group — Mollusca — 

 some of which are found in tiie Lower Silurian, though the 

 latter comprises forms less actively pelagic. Mr. Wallace 

 thinks fishes less cosmopolitan than mollusks, a feature he 

 attributes to the antiquity of the shell-fishes ; but it may be 

 due to other causes, such as food and temperature, which keep 



* ' Die Verbrcitung der Fischc ' (Prag-, 189-3). 



