The Powan of Loch Lomond 253 
ce) 
long by 5 miles wide at its greatest breadth, and contains twenty-four 
islands, some of which are very large. It is thus a perfect breeding- 
place for crustacea, and there being so little run on the loch, they are 
not carried away. In this respect it resembles a town’s reservoir with 
screens at the outlet so fine that daphniz cannot pass through, 
with the result that inside the reservoir is a mass of insect life, and 
trout brought among them have only to open and close their mouths 
to get enough food to sustain them and make them grow to a large 
size. See photograph of daphnic taken from the stomach of a powan 
(ioe 23 ). 

Fic, 231.—Daphnie, life size. 
