ssed ancestral tentacular experience,
which, originally a stimulation producing intense agitation and alarm, has
now become merely a play activity and a source of keen pleasure.[9]

We need not, however, go so far back in the zooelogical series to explain
the origin and significance of tickling in the human species. Sir J.Y.
Simpson suggested, in an elaborate study of the position of the child in
the womb, that the extreme excitomotory sensibility of the skin in various
regions, such as the sole of the foot, the knee, the sides, which already
exists before birth, has for its object the excitation and preservation of
the muscular movements necessary to keep the foetus in the most favorable
position in the womb.[10] It is, in fact, certainly the case that the
stimulation of all the ticklish regions in the body tends to produce
exactly that curled up position of extreme muscular flexion and general
ovoid shape which is the normal position of the foetus in the womb. We may
well believe that in this early developed reflex activity we have the
basis of that somewhat more complex ticklishness which appears somewhat
later.

The mental element in tickling is indicated by the fact that even a child,
in whom ticklishness is highly developed, cannot tickle himself; so that
tickling is not a simple reflex. This fact was long ago pointed out by
Erasmus Darwin, and he accounted for it by supposing that voluntary
exertion diminishes the energy of sensation.[11] This explanation is,
however, inadmissible, for, although we cannot easily tickle ourselves by
the contact of the skin with our own fingers, we can do so with the aid of
a foreign body, like a feather. We may perhaps suppose that, as
ticklishness has probably developed under the influence of natural
selection as a method of protection against attack and a warning of the
approach of foreign bodies, its end would be defeated if it involved a
simple reaction to the contact of the organism with itself. This need of
protection it is which involves the necessity of a minimal excitation
producing a maximal effect, though the mechanism whereby this takes place
has caused considerable discussion. We may, it is probable, best account
for it by invoking the summation-irradiation theory of pain-pleasure, the
summation of the stimuli in their course through the nerves, aided by
capillary congestion, leading to irradiation due to anastomoses between
the tactile corpuscles, not to speak of the