252 Flow 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. . . . Inthe 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 aberrations 
are considered to be the result of inter-breeding, due to an 
extreme degree of isolation” ( Yorkshire Vertebrata, p. 127). It 
is quite likely that deficient gill-covers are in many cases due to 
inter-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 cases the deformity would prove here- 
ditary we have at present no means of knowing, as such fish are 
never kept to breed from. J have had opportunites 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 livia). 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 
