56 MR. J. C. MOTTKAM ON THE 



do constantly reour among insects, both in the larva and adult states. It 

 follows that in this case unpalat ability might be associated in the prej'er's 

 mind, not with a particular form, colour, pattern, or other character, but with 

 conspicuousness. If a bird be given a conspicuous insect which it has never 

 before seen it will be shy in attack ; whereas when the insect is inconspicuous 

 the bird's attack will be bolder. Variations in edibility may be associated 

 in the preyer's mind with degrees of conspicuousness rather than with 

 distinctive markings : many distinctive marks appear to be related to con- 

 cealment rather than the reverse ; nevertheless, as a working hypothesis, 

 Swynnerton's conception may prove to be of considerable value. 



(3) Birds have been observed sometimes to exercise no choice with respect 

 to butterflies on which they are feeding. As has been already seen, the 

 conclusion that they do not recognise a difference in palatability cannot be 

 drawn. 



(4) Birds have been sometimes observed feeding upon presumably pro- 

 tected butterflies, Euploeines and Danaines. Conclusions cannot be drawn 

 that they are not relatively unpalatable ; trout will sometimes feed upon 

 tadpoles. 



(5) Birds have on a few occasions (4) been observed to feed upon some 

 butterflies, whilst neglecting others. This might be the result of a temporary 

 special appetite of the bird, the difference in the ease of capture of the 

 insects, or by a difference in the relative prevalence of the insects. Only 

 after exclusion of these and other factors can it be concluded to be due to a 

 difference in palatability. 



PART 2. 



Observations ivltich slioio that Salmo fario mistakes other things for Floating 

 Insects, and fails to distinguish Artificial Flies from Natural Ones. 



As already mentioned, examination of the alimentary contents often reveals 

 the presence of small pieces of wood, stick, grass-stem, and seeds, more 

 especially grass-seeds. If a trout, which is feeding on floating insects, be 

 observed over a long period, it will be seen often closely to examine many 

 such small floating things ; the majority of these the fish will neglect, a few 

 will be taken into the mouth to be at once rejected, a small proportion is 

 swallowed. There can be no doubt that the fish mistakes these things for 

 the insect on which the fish is feeding at the time, and it may be concluded 

 that its vision is not very acute. If the fish is feeding on one particular 

 insect, as is most often the case in chalk-streams, mistakes are much more 

 seldom made than when the fish is feeding on any floating insect which the 

 stream may bring down. 



