he concludes, "suggests that the accepted male is the one which adequately
evokes the pairing impulse.... Courtship may thus be regarded from the
physiological point of view as a means of producing the requisite amount
of pairing hunger; of stimulating the whole system and facilitating
general and special vascular changes; of creating that state of profound
and explosive irritability which has for its psychological concomitant or
antecedent an imperious and irresistible craving.... Courtship is thus
the strong and steady bending of the bow that the arrow may find its mark
in a biological end of the highest importance in the survival of a healthy
and vigorous race."

Having thus viewed the matter broadly, we may consider in detail
a few examples of the process of tumescence among the lower
animals and man, for, as will be seen, the process in both is
identical. As regards animal courtship, the best treasury of
facts is Brehm's _Thierleben_, while Büchner's _Liebe und
Liebes-Leben in der Thierwelt_ is a useful summary; the admirable
discussion of bird-dancing and other forms of courtship in
Häcker's _Gesang der Vögel_, chapter iv, may also be consulted.
As regards man, Wallaschek's _Primitive Music_, chapter vii,
brings together much scattered material, and is all the more
valuable since the author rejects any form of sexual selection;
Hirn's _Origins of Art_, chapter xvii, is well worth reading, and
Finck's _Primitive Love and Love-stories_ contains a large amount
of miscellaneous information. I have preferred not to draw on any
of these easily accessible sources (except that in one or two
cases I have utilized references they supplied), but here simply
furnish illustrations met with in the course of my own reading.

Even in the hermaphroditic slugs (_Limax maximus_) the process of