associated with sex are as a rule among the most complex features of the body. Some animals, to be sure, simply discharge their sex cells into the water, leaving their union to chance, but in the majority of cases, especially in higher forms, there exist elaborate mechanisms to insure the meeting of these cells. Correlated with these structures we find mating instincts which frequently manifest themselves in complex modes of behavior. More acute senses have been evolved in many cases very largely for effecting the meeting of the sexes. The large antennæ of male moths, the large eyes of the common drone bee, and the auditory apparatus of the male mosquito are a few of the countless illustrations of this fact. The various apparatus in insects for making sounds which are found in crickets, locusts, cicadas, etc., are devices for securing the meeting of the sexes, and the complementary development of the auditory apparatus in the same insects has doubtless been furthered through the evolution of these structures.
Much of the elaborate organizations of the imago stage of insects has reference, directly or indirectly, to activities concerned in mating and depositing the eggs in the proper environment for the development of the young. There is a relatively long larval or nymphal period chiefly devoted to the vegetative functions of assimilating nutriment and growth; in many cases the imago takes no food, or need take none, before the eggs are fertilized and laid; and in several species the mouth parts have become so completely atrophied that food taking is impossible. Mating not infrequently occurs soon after the insects emerge from the pupal covering. In the may-flies, which live but a short time in the winged state, in order to mate and deposit their eggs it is probable that the imago stage would long ago have disappeared were it not retained as a means of effecting the union of the sexes. The same is doubtless true of many other insects. The activities of the imago state, broadly speaking, are primarily altruistic; they are concerned mainly with the welfare of other members of the species. They are also expensive. In the winged state numerous new enemies are encountered and many lives are lost. In the pupa stage which prepares for it there is commonly an extensive tearing down of old structures and the building up of new ones, during which the insect is helpless against many enemies.
Mating activities are almost everywhere among the most complex performances of an animal's life. The opposite sex must be distinguished from all other creatures and responded to accordingly. Often pursuit and capture or winning over are the necessary preliminaries to sexual union. All this puts a premium, so to speak, on the sharpening of the senses, the development of strength and activity, and the evolution of the higher psychical qualities. Consider the mating activities of crustaceans, the courtship of spiders, the breeding habits of fishes, and still more the elaborate wooing of male birds, and it will become manifest how
