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 (_a_) _under compulsion_, as when it is her last resort in self-defence; (_b_) _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; (_c_) or finally, _under 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 intelligence, if any, _Clepsine_ may have. Nor, indeed, is it an easy matter to determine. The differential reaction according as the animal has eggs or not suggests intelligence; but it may be instinct varying according to the conditions of stimulation external and internal. The different behaviour which may be seen in different cases when a stone is turned to the light again suggests intelligence, but again may be determined directly by the conditions of stimulation. Prompted by Dr. Whitman’s observations, I endeavoured to determine whether a leech would grow accustomed to frequent gentle stimulation with a camel’s-hair brush, and cease to react under circumstances which were followed by no ill effects. But though I incline to think that this is the case, the observations were not such as to be satisfying and convincing. If intelligence be present we seem to find it in an early and rudimentary state.