What is true for birds is even more obvious for spiders where the special ornaments are not confined to parts of the body with high muscular development, etc. The writers make the very pertinent criticism that while Wallace objects to assuming the emotional states in females, he is less careful in regard to the males’ emotions when he speaks of the display “under the influence of jealousy or sexual excitement.... The males, in their rivalry with each other, would see what plumes were most effective; and each would endeavor to excel his enemy as far as voluntary exertion would enable him.”[13]
“If the males have so complex an emotion as jealousy, and further, if they are conscious of the value of the plumes, may it not be asked why the female is unable to ‘see what plumes are most effective?’ The mental state in the male is without meaning unless we suppose the female to be affected and pleased.” (Peckham, loc. cit., p. 144.)
In regard to another interpretation of the courtship, the Peckhams point out:
“Mr. Pocock has suggested that the attitude of observant interest on the part of the female spider might be taken to indicate that she was preparing to spring upon her mate and devour him; or that it might simply mean that she was warily guarding herself from his approach. Neither of these suppositions is admissible. In some species the male is not attacked by the female, and when she does wish, as frequently happens, either to avoid or to destroy him, her attitude is totally different. In the former case she turns about and runs rapidly away, or suspends herself by a thread of web. In the second, there is a contraction of all the muscles, the legs are drawn together, and in this crouching position she creeps slowly toward him, as she might if he were a fly, only with something more malignant in her aspect. When she takes this stand the male incontinently flees. When, on the contrary, the female is interested in the male display, she seems perfectly absorbed in watching him, the muscles are all relaxed, unconscious of herself she directs her glance now here, now there, as he moves about; as he continues his mad antics, her appearance gives every indication of pleasurable excitement, and as he comes closer and closer, she yields herself to the impulses which he has awakened in her, and, as in pulex, joins in his dance and whirls around and around as though intoxicated. We claim, then, to have completely answered Mr. Wallace’s first objection.” (Peckham, loc. cit., pp. 145, 146.)
Finally, in regard to the specific character of the display of the males, the Peckhams make the following significant statement:
“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.
Montgomery, who made observations on the courting habits of several species of spiders, states that his “general theoretical conclusions were quite different from those of the Peckhams.” It turns out, however, that his objection to their view is based entirely on their assumption that the male is conscious of his display and that the female is guided by an esthetic sense in selecting the more beautiful male. It should be pointed out that even after the removal of these gratuitous assumptions as to the cause of the evolution of the male and female, enough still remains in Montgomery’s own observations to include his results on courtship under Darwin’s theory of sexual selection. For example, Montgomery says:
“The adult male is excited simultaneously by fear of and desire for the female, and his courtship motions are for the most part exaggerations of ordinary motions of fear and timidity. By such motions he advertises himself to the female as a male, but there is no proof that he consciously seeks to arouse her eagerness by esthetic display—there seems to be no good reason to hold that the female is actuated in her choice by sensations of beauty.... Thus my opinion was opposed to Darwin’s theory.”