2 18 
of the agent of selection, Natural Selection would not come 
into play at all. Or, on the other hand, a species of in 
sect-eater, which lived on one particular species of victim, 
might prefer to eat the slightly nauseous victim instead 
of attempting the radical change of seeking a new source 
of food altogether. It is natural to suppose that it would 
attempt the former course, seeing that it must have studied 
the habits of its victims and could catch them more easily 
than others. It has been ascertained that certain species 
do restrict themselves to one particular victim. Thus 
Mr. Bates tells us :— 
“We have proof, in the case of sand-wasps, which provision their 
nests with insects, that a single species is very generally selected out 
of numbers, even of the same genus, existing in the same locality. I 
was quite convinced in the case of Cerceris binodis of South America, 
which destroys numbers of a Megalostomis (family Clythridce), that 
the great rarity of the beetle was owing to its serving as prey to the 
Cerceris.”—(Transactions of the Linnean Society, vol. xxiii., pari j, 
P• 5H-) 
In this case all would be alike eaten, and there would be 
no Natural Selection. 
Let us now take the alternative explanation ; that an 
edible form first began to develop a slightly nauseous taste 
in some individuals which still remained unchanged in 
outward form. In that case, they could not be dis 
tinguished from their unmodified companions. Two very 
opposite results have been conjectured as ensuing from 
this fact. Mr. Wallace asserts that the modified insects 
would be attacked just as much as ever. 
“ If any particular butterfly of an eatable group acquired the 
disagreeable taste of the Heliconias, while it retained the charac 
teristic form and colouring of its own group, this would really be of 
no use to it whatever ; for the birds would go on catching it among 
its eatable allies (compared with which it would rarely occur), it 
would be wounded and disabled even if rejected, and its increase 
would thus be as effectually checked as if it were devoured.”— 
{Contributions, p. 81.)