76 BRITISH FRESH-WATER FISHES 
in colour than the female, and in both sexes the iris is 
red. The fish possesses no air-bladder, and the stomach 
is a capacious round sac, lined internally with a black 
pigment. 
The species is very widely distributed, very few water- 
sheds being without it between Britain and Siberia, France and 
Northern Asia, where its place is taken by other 
species in that region and North America. But the 
miller’s thumb is so scarce in Irish waters that its very 
existence has been denied, and it has not been recorded from 
Spain or Greece. Personally, I have never seen this species 
in Scotland. 
In habit, the miller’s thumb is the reverse of obtrusive ; 
its custom is to lie under a stone, with the gaping mouth ready 
to seize any passing insect. Izaak Walton says that 
“in very hot days he will lie a long time very still, 
and sun himself, and will be easy to be seen upon any flat stone 
or gravel,” which reads like a piece of genuine observation. 
Other writers have repeated this statement, but whether 
founded upon what they have seen or only upon what they 
have read, the present deponent sayeth not. Inasmuch as I 
have not happened to witness this habit in the miller’s thumb, 
albeit I have wasted more time by the waterside than it is 
creditable to record, I am not qualified either to confirm or 
deny this behaviour of the fish in question. Usually its 
leading motive seems to be keeping out of sight, as if conscious 
of its own ugliness. 
The spawning takes place early in spring, when the female 
deposits bunches of rosy-tinted ova in what is called by 
courtesy a nest, but which is nothing more than a natural 
depression in the sand or gravel, or one worked out by herself. 
Having performed this part of the domestic economy, it is 
said that the prolific mother retires from the nest, and leaves it 
to the protection of her mate, who watches it carefully for four 
or five weeks, and does his best to repel the attacks of 
Distribution, 
Habits. 
