THE NATURE OF INTELLIGENT BEHAVIOUR 121 
in the precision ; and fourthly, in dealing with the circum- 
stances in such a way as to extract from them the maximum 
of benefit. 
Tf, however, we are to regard these severally as criteria of 
intelligence, each should serve to differentiate intelligent from 
instinctive behaviour. But this is not the case. The precision 
of the adjustment can- 
aot be regarded as a cri- 
terion of intelligence, for 
many instinctive acts are 
remarkably precise. No 
grocer’s assistant rolls a 
paper funnel with more 
precision than is dis- 
played by the birch-wee- 
vil (Rhynchites betule) in 
constructing the leaf- 
case in which her eggs 
are laid. Curved inci- 
sions of constant form 
are made on either side 
of the midrib, and are 
“of just the right shape 
to make the overlaps in 
the rolling, and to re- 
tain them rolled up 
with the least tendency 
to spring back,” * while the tip of the leaf is rolled into 
a second smaller funnel, which is tucked in to close the 
opening of the first, after the eggs have been deposited. “The 
eggs hatch in their dark place, each giving rise to an eyeless 
maggot, which ultimately leaves the funnel for the earth. . . . 
Hence the beetle cannot be considered to have ever seen a 
funnel, and certainly has never witnessed the construction of 
1 
Fig. 18.—Leaf-case of Birch-weevil. 
* See D. Sharp, “Cambridge Natural History,” “ Insects,” part ii., 
p. 293, and the original authorities cited on p. 294. 
