XXXIX, x1] (255 }) 
general sacrifice to the inexperience of insectivorous enemies 
would be divided between them. 
This theory was published in 1879. Nine years previously 
Miiller had made a tentative suggestion that the resemblance 
between protected genera had been brought about by sexual 
selection. It is this theory which Darwin described as 
“rather too speculative to be introduced into my book,” and it 
is also the theory which Professor Packard regarded as the 
accepted Mullerian hypothesis. The error has been very fully 
pointed out by Professor Meldola in a letter to “ Nature” 
published in November 1905, and materially affects the value 
of Professor Packard’s criticisms. 
Mr. Abbot H. Thayer’s view that the colours of animals are 
such as to cause the creature to cease to appear at all, appears 
to be merely a universal application of the theory of cryptic 
coloration. Instances of eryptic coloration are too common to 
admit of any doubt whatever, but to maintain that every 
animal is coloured for concealment appears to me to be too 
much of a generalization. Probably few would deny that 
warning colours are exhibited by many stinging insects, dis- 
tasteful caterpillars and other offensive creatures, to take only 
the insects alone. Mammals and reptiles, however, are also 
known to exhibit warning colours, as for instance the skunk with 
its white tail, the coral snake, and certain brightly coloured 
frogs described in Mr. Belt’s “Naturalist in Nicaragua.” 
The warning colours exhibited by certain caterpillars have 
formed the subject of much experiment by well-known inves- 
tigators, and all are agreed that insect-eating animals refuse 
those larvee which possess conspicuous coloration. 
Professor Packard next proceeds to emphasize the paucity 
of evidence on which rests the theory that insectivorous birds 
are the principal agents of natural selection in Lepidoptera. 
Here I feel myself bound to agree that the recorded instances 
of butterflies forming the staple food of birds are few and far 
between. It would at first sight appear that if birds are really 
the principal cause of modification in the markings of butter- 
flies’ wings there ought to be no necessity for the supporters 
of the Bates-Miiller theories to be obliged to seek out instances 
of birds eating butterflies. It should be generally recognized 
