THE TROUT 69 



considered to be the result of interbreeding, due to 

 an extreme degree of isolation. The isolation of 

 Malham Tarn is complete ; it has no feeders of 

 sufficient size for the introduction of new blood, 

 while the overflow is absorbed by fissures in the 

 limestone, after being swallowed up by which the 

 water reappears as the River Aire after a subter- 

 ranean course of two miles. The beck at Penyghent 

 is exceedingly small, and after a short half-mile 

 course disappears in a similar manner." 



In Loch-na-Maorachan in Islay occur the so- 

 called " tailless " Trout, in which the caudal fin-rays 

 are abnormally short and have their ends curved 

 together, the anal fin and sometimes also the paired 

 fins possessing this peculiarity to a less extent. 

 Dr. Traquair has reported on these and on similar 

 Trout from other Scottish localities, but has only 

 reached the conclusion that none of the causes 

 assigned, such as wearing ofT of the fins against the 

 rough bottom, nibbling by other fish, deficiency of 

 lime in the water, etc., are adequate to produce this 

 effect. 



Hump-backed or Hog-backed Trout, with the 

 body abnormally short and deep, occur in several 

 localities in our islands and elsewhere they have 

 a malformed vertebral column, sometimes curved, 

 usually with a number of vertebrae shortened and 

 coalesced to a considerable extent. In 1747 

 Mr. Barrington pointed out that the " Hog-backed 

 Trout of Plinlimmon " occurred only in districts 

 where there were falls, and he advanced the theory 

 that the eggs or fry were washed over, thus sustain- 

 ing spinal injuries which led to a shortening of the 

 vertebral column. In 1886 Day proved experi- 



