252 How to obtain it. 



Malham Tarn, and in a beck on the western side of Penyghent. 

 This is manifested in the former by the deficiency in the gill-cover 

 in about one in every fifteen fish caught. ... In the case of 

 the ground trout of Penyghent as they are called, Mr. John 

 Foster informs us that the malformation consists of a singular pro- 

 jection of the under jaw beyond the upper. These abberations 

 are considered to be the result of inter-breeding, due to an 

 extreme degree of isolation " (Yorkshire Vertebiata, p. 127). It 

 is quite likely that deficient gill-covers are in many cases due to 

 in-breeding; certain it is that they can be caused by an attack 

 of fungus when the fish is young, or by an epidemic of gill fever. 

 How far in the two latter oases the deformity would prove here- 

 ditary we have at present no means of knowing, as such fish are 

 never kept to breed from. I have had opportunities of watching 

 to some extent cases of head and jaw deformity, and have known 

 them developed in fish that have passed scrutiny as yearlings, but 

 have been deformed at the two-year-old stage. 



That some deformities are not apparent until fish are well 

 advanced in life is certain. I have tried the experiment of breed- 

 ing from deformed parents, but the progeny showed no trace of 

 the deformity. On the other hand some fish culturists have suc- 

 ceeded in cultivating races of deformed gold fish which are now 

 well known in our markets. Here the deformity is hereditary, 

 and we find the same to be the case with some birds, the different 

 varieties of fancy pigeons being produced from the wild rock dove 

 (Columba livid}. Amongst domestic fowls and animals the same 

 tendency develops, and we know what great importance attaches 

 to it. An exhibitor at one of our poultry shows failed to obtain a 

 prize for a very fine bird, which to him and some of his friends 

 seemed perfect in every point. He appealed, and some discussion 

 followed, when the reason was given for withholding the prize. 

 The bird had a crooked breast-bone, and was entirely useless for 

 breeding purposes. It was otherwise perfect, and this point had 

 either been overlooked by the exhibitor or he had hoped it would 

 not be noticed. Amongst cattle and horses, too, we know what 

 importance is attached to the different "points," and what an 

 amount of skill and judgment is required in the breeding of 

 pedigree stock. So amongst trout, too much care cannot be 



