In the immense class of insects the sexes sometimes differ in their
locomotive-organs, and often in their sense-organs, as in the
pectinated and beautifully plumose antennae of the males of many
species. In Chloeon, one of the Ephemerae, the male has great pillared
eyes, of which the female is entirely destitute. (1. Sir J. Lubbock,
Transact. Linnean Soc. vol. xxv, 1866, p. 484. With respect to the
Mutillidae see Westwood, Modern Class. of Insects, vol. ii. p. 213.)
The ocelli are absent in the females of certain insects, as in the
Mutillidae; and here the females are likewise wingless. But we are
chiefly concerned with structures by which one male is enabled to
conquer another, either in battle or courtship, through his strength,
pugnacity, ornaments, or music. The innumerable contrivances,
therefore, by which the male is able to seize the female, may be
briefly passed over. Besides the complex structures at the apex of the
abdomen, which ought perhaps to be ranked as primary organs (2. These
organs in the male often differ in closely-allied species, and afford
excellent specific characters. But their importance, from a functional
point of view, as Mr. R. MacLachlan has remarked to me, has probably
been overrated. It has been suggested, that slight differences in these
organs would suffice to prevent the intercrossing of well-marked
varieties or incipient species, and would thus aid in their
development. That this can hardly be the case, we may infer from the
many recorded cases (see, for instance, Bronn, Geschichte der Natur,
B. ii. 1843, s. 164; and Westwood, Transact. Ent. Soc. vol. iii.
1842, p. 195) of distinct species having been observed in union. Mr.
MacLachlan informs me (vide Stett. Ent. Zeitung, 1867, s. 155) that
when several species of Phryganidae, which present strongly-pronounced
differences of this kind, were confined together by Dr. Aug. Meyer,
THEY COUPLED, and one pair produced fertile ova.), it is astonishing,
as Mr. B.D. Walsh (3. The Practical Entomologist, Philadelphia, vol.
ii. May 1867, p. 88.) has remarked, how many different organs are
worked in by nature for the seemingly insignificant object of enabling
the male to grasp the female firmly. The mandibles or jaws are
sometimes used for this purpose; thus the male Corydalis cornutus (a
neuropterous insect in some degree allied to the Dragon flies, etc.)
has immense curved jaws, many times longer than those of the female;
and they are smooth instead of being toothed, so that he is thus
enabled to seize her without injury. (4. Mr. Walsh, ibid. p. 107.) One
of the stag-beetles of North America (Lucanus elaphus) uses his jaws,
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