PmiLLrIPPS.—Food-supply and Deterioration of Trout. 389. 
to regard only the three first named in the table (Chironomus, Corethra, 
and Trichopter larvae and pupae) as of any considerable importance 
to the trout. To my mind the chief value of this table is that it clearly 
been eaten by the trout. The largest number eaten by a single trout was 
351, while three trout had eaten none at all.” Needham carried out an 
interesting experiment by feeding a dragon-fly nymph, Libellula pulchella, 
on Corethra. On p. 210 he states: “ Placed in the nymph's mouth they 
were eaten with avidity; but placed thickly in the water with it, and 
In regard to the suitability of insect food as opposed to fish food for trout, 
Atkins (1910, pp. 841-51) has shown the potency of the larvae of flies in 
promoting growth. Experiments carried out by him showed that the fry 
of salmon fed with insect-larvae exceeded in growth by 27 per cent. those 
on chopped meat. Whether adult trout fed on insect-larvae would thrive 
to a greater extent than those fed on small fishes remains yet to be proved. 
The enormous number of insect-larvae which would be required to equal, 
for commercial purposes. An interesting note in regard to the mortality 
mortality could be checked in the course of two weeks by changing to a 
diet of some fresh meat." 
Kendall (1918, p. 534) states that the general food-supply upon which 
аз ; Б 
urther, he adds that in all waters there is а seasonal supply of insect- 
larvae which varies with the season and locality ; but where food in the form 
of fishes is available the insect food appears to be more or less neglected, 
particularly by the larger fish. 
This statement is interesting when Salmonidae are considered in the 
light of evolution. It is now recognized that the family as it exists to-day 
is derived from an ancestral form which existed about the Cretaceous 
period, and whose natural habitat was the ocean. It will be seen that many 
of the same types of food may have been utilized by the ancestral form, 
with the exception of insects. Accordingly insects and insect-larvae have 
gradually entered into the category of food-supply as Salmonidae have 
taken to rivers and streams. 
