160 INTELLIGENT BEHAVIOUR 
This behaviour shows a surprising keenness of tactile sensi- 
bility, the least touch of the water with a needle-point being 
felt at once. . . . If its back were rubbed with a brush or the 
handle of a dissecting needle, in order to test its sensitiveness 
to touch, the appearance would probably be that of insensi- 
bility and indifference to the treatment. Closer examination, 
however, would show that the flesh of the animal was more 
rigid than usual, and that the surface was covered with 
numerous stiff, conical elevations, the dermal papillee or warts, 
which are so low and blunt in the normal state of rest as to be 
scarcely visible. It would be seen that the animal, although 
motionless, was in a state of active resistance to attack... . 
Clepsine has another and entirely different method of keeping 
quiet. The animal rolls itself up (head first and ventral side 
innermost) into a hard ball, outwardly passive, free to roll or 
fall whithersoever gravity or currents of water may direct 
it... . If by chance the animal has eggs, it will not desert 
them to escape in this way. . . . This species, then, has two 
quite distinct and peculiar ways of keeping quiet, and thus 
avoiding its enemies. If the animal has no eggs, or if it has 
young, it may adopt either mode of escape, while if it has eggs 
it has no choice but to remain quiet over them. . . . The act 
of rolling up into a passive ball may be performed (@) under 
compulsion, as when it is her last resort in self-defence ; 
(0) under a milder provocation, aS one of three courses of 
behaviour, as when the resting-place is turned up to light, and 
the choice is offered between remaining quiet in place, creeping 
away at leisure, or rolling into a ball and dropping to the 
bottom ; (¢) or finally, wnder no special external stimulus, but 
rather from internal motive, the normal demand for rest and 
shady seclusion, presumably very strong in Clepsine after 
gorging itself with the blood of its turtle host.” 
Professor Whitman rightly regards the act of rolling into 
a ball as instinctive, and due to natural selection. But he does 
not undertake to discuss the question as to how much intelli- 
gence, if any, Clepsine may have. Nor, indeed, is it an easy 
matter to determine. The differential reaction according as 
