158 INTELLIGENT BEHAVIOUR 
that re-presentative states are evoked through the mediation of 
presentative sense-impressions. But how difficult, if not im- 
possible, it is to form anything like a satisfactory conception 
of the rudimentary mental processes of a limpet ! 
The most highly developed molluscs are the cephalopods. 
They have long sensitive mobile arms with which they feel for 
and capture their prey. ‘‘ Now Schneider observed,” writes 
Dr. Stout,* “a very young octopus seize a hermit-crab. The 
hermit-crab covers the shell in which it takes up its abode 
with stinging zoophytes. Stung by these, the octopus imme- 
diately recoiled and let its prey escape. Subsequently it was 
observed to avoid hermit-crabs. Older animals of the same 
species managed cleverly to pull the crab out of its house 
without being stung.” Such cases afford evidence of profiting 
by experience through the exercise of intelligence. 
Darwin’s careful observations on the manner in which 
earthworms drag leaves into their burrows seem to show that 
these annelids act intelligently, and deal with leaves of different 
shapes in different ways. The leaves of Pine trees, consisting 
of two needles arising from a common base, were almost 
invariably drawn down by seizing this basal point of junction ; 
while the leaves of the Lime were, in 79 per cent. of the 
cases examined, drawn down by the apex; in only 4 per 
cent. by the base; and in the remaining 17 per cent. by 
seizing some intermediate portion. On the other hand, the 
leaves of the Rhododendron, in which the basal part of 
the blade is often narrower than the apical part, were in 
66 per cent. of the observations drawn down by the narrower 
base. ‘Triangles of paper were in the majority of cases 
seized by the apex. Commenting upon his observations, 
carried out with great care under experimental conditions, 
Darwin says,f ‘‘ As worms are not guided by special instincts 
in each particular case, though possessing a general instinct to 
plug up their burrows, and as chance is excluded, the next 
most probable conclusion seems to be that they try in different 
* “ Manual of Psychology,” p. 257. 
t “ Vegetable Mould and Earthworms,” p. 95. 
