136 THE ZOOLOGIST. 
invaluable museum. He even did more than this—he investi- 
gated the reason why these muscular stomachs existed. Haviug 
obtained a young sea-gull he gradually brought it to live entirely 
upon corn. Here the muscular walls of the stomach became 
thickened, in order to permit the bird, under the changed con- 
ditions as to food from what normally occurs, to accommodate its 
stomach to its newrequirements. ‘This organ had to grind up its 
hard corn, to do which its muscular walls became preternaturally 
developed. Dr.John Davy remarked that the river Trout, when 
feeding chiefly on incased larvee, acquires a stomach of unusual 
thickness, like the Gillaroo Trout of many of the Irish lakes 
where they feed chiefly on shellfish. Sir Humphrey Davy, in 
1827, writing about the Charr of the Leopoldstein Lake, and 
those of the Lake of Borguet, observed :—‘I am induced to 
make some observations on the physical causes which by changing 
the habits in many generations may change the forms of fish. 
The Trout, when it feeds principally on fish, must be extremely 
active and strong, consequently from its predatory mobile habits 
acquires large teeth, large fleshy fins, thick skin, and great 
pectoral fins for turning. When it feeds on shellfish it gets 
the stomach of the Charr and its colours, as in the Gillaroo 
Trout.” But if the Gillaroo Trout is a distinct species, it 
appears by similar reasoning that when other forms of this genus 
have their stomach thickened, they also should have specific rank 
accorded. Thompson remarked :—“ The coats of the stomachs 
of other species of Salmones than S. fario (of which only the 
Gillaroo is set down as a variety) become muscular from the same 
cause. I have seen S. ferox from different localities with a 
muscular stomach, and these examples were called Gillaroo 
Trout by persons who distinguish them from the ordinary state of 
the fish, believing them to be a distinct species.” If the Gillaroo 
is merely a variety, what will be the effect of introducing it into 
our English streams, as is now proposed ? It will simply be that 
it will revert back to the Common Trout when unable to obtain a 
supply of shellfish. That crossing or intermingling forms from 
different places improves the breed of Salmon and Trout was 
long since pointed out, but whether the Gillaroo is one well 
adapted for importing may be open to question. A recent author 
gives as one distinguishing feature its inferior flavour; but this 
of course may be due to the food it indulges in. In the County 
