igoi] Prince— Adaptation in Fishes. 213 



implied in this chang^e of environment is most remarkable, and 

 appears, in many instances at least, to be acquired during the life 

 of the individual. Thus, a newly-hatched salmon soon dies if 

 placed in sea-water, and the eggs of that species are also fatally 

 " affected by the same treatment ; yet later in life the salmon lives 

 indifferently in salt water and in river water. Further, many 

 species, which normally migrate, have lost the habit and, like the 

 land-locked salmon, smelt, flounder, or herring, may pass their 

 days without ever tasting salt water. Some curious instances of 

 extreme changes of habitat in certain moUusks are on record, as, 

 for instance, the bed of cockles {Cardium edule) which was des- 

 cribed before the Wernerian Society in Edinburgh in 1825 as 

 existing in a Yorkshire peat moss 40 miles trom the sea. These 

 shell-fish lived in a sandy channel, communicating with the river 

 Tees, and were precisely like those distributed over the vast beds, 

 eight or ten square miles in extent, at the estuary of that river. 

 To the taste, however, they were distinctly less salt in flavour. 

 A Mr. Brand, more than a hundred years earlier, had described, 

 in an account of the Orkney Isles, a bed of cockles in the fields a 

 mile from the sea. They were in a deep furrow to which salt 

 water might have had access during an exceptional storm. 

 Specimens of the sea-whelk [Buccinum iindatum) have been found 

 in a fresh-water lake on the island of Yell, a mile and a half from 

 the sea, and as the apex or tip was fractured it was thought that 

 sea-birds or crows had carried them to their new location. Yet, 

 the shell being somewhat thinner in texture, and more distinctly 

 banded, it seems more probable that they had lived tor a long 

 period in their fresh-water environment, and thus differed from the 

 marine forms. 



Oysters, as is well known, flourish in brackish water, and 

 can endure transference to water almost destitute of salinity ; but 

 the}' do not appear to breed or maintain a healthy state, they 

 merely fatten and increase in size. 



Many fishes in the same way are unfavourably affected if pre- 

 vented from performing their usual migrations from or to salt 

 water. Dr. Barfurth discovered that the ovaries become diseased, 

 and the eggs degenerate in fishes which are prevented from 

 normally migrating. The same observer has recorded the fact 



