“The spider has four pairs of legs, and all are equally available for display or locomotion, and since all the movements are slow and on the ground they are entirely open to observation and study, and we are thus in a position to decide by facts whether their activity is simply an outlet for superfluous energy, and therefore meaningless, or whether there is a purpose in it. If the purpose of the antics is only to let off energy, then we should expect one pair to be flourished around quite as often as another, and that the pair flourished should as frequently be one that was not ornamented as one that was; and, moreover, their movements ought not to be of such a nature as to display the color or ornament, more frequently than the law of chance would explain. If the spider almost always moves the ornamented legs, and in such a way, too, as to bring out their beauty, it would seem to us, to say the least, highly improbable that the dance of the spider was merely a meaningless overflow of surplus energy. Such an explanation leaves much that needs explanation. The facts are, that the best foot is put forward; and this is just what Darwin’s theory requires and explains. Under Mr. Wallace’s view the facts are inexplicable. The better to show that these movements are not simply meaningless outlets of high vigor, we illustrate the several positions by figures taken from nature (figs. 7-12). The figures would seem to prove that the legs that are ornamented or contrasted in color are also the legs that are usually flourished; that where none of the legs have special ornament, then all are used; or, as sometimes happens, when an unornamented leg is used the movements are of such a character as to display some ornament that would otherwise have been more or less hidden from the female.” (Peckham, _loc. cit._, p. 147.) In the tarantula, Petrunkewitsch finds that sight plays no rôle in mating--that it is due entirely to accidental contact between the male and female. Here the sexes are closely alike, except for a pair of hooks on the front legs of the male, by means of which he grasps the mandibles of the female, holding them during the elaborate process of transference to her genital opening the sperm that he has already collected in the genital spoon on his palpi. The hooks serve to guard the male against injury or death, while at the same time they aid him in the act of coitus. In a common spider, _Mœvia villata_, two kinds of males exist. Both have been seen to mate with the same female. No preference is given to either type. The difference between them, according to Painter, is connected with or caused by an additional pair of chromosomes in the gray male. The two types may therefore have no connection with sexual selection, but be directly due to a difference in the chromosome group.