Our knowledge of Spiders under the afflatus of sexual desire has been immensely increased by the long and patient observations of Mr. and Mrs. Peckham. The fact that their investigations were carried on with captive specimens, and therefore under artificial conditions both as to environment and the number of individuals placed together at one time, must not be lost sight of; nor must we forget that they worked under the firm conviction that the Sexual Selection theory of choice by the females was an indisputable fact. Wherever colour was present they looked for, and saw, evidence that the female appreciated such hues, though from their observations it would seem that dull-coloured species behaved as though they were suffused with resplendent hues. In the course of their studies the courtship of several species was investigated, but a summary of their results is all that can be given here. _Saitis pulex_ formed the subject of one of their experiments. A male was placed in a box containing a mature female. “He saw her as she stood perfectly still, twelve inches away; the glance seemed to excite him and he moved towards her; when some four inches from her he stood still, and then began the most remarkable performance that an amorous male could offer to an admiring female. She eyed him eagerly, changing her position from time to time so that he might be always in view. He, raising his whole body on one side by straightening out the legs, and lowering it on the other by folding the first two pairs of legs up and under, leans so far over as to be in danger of losing his balance, which he only maintains by sidling rapidly towards the lowered side. The palpus, too, on this side was turned back to correspond to the direction of the legs nearest to it. He moved in a semicircle for about two inches, and then instantly reversed the position of the legs and circled in the opposite direction, gradually approaching nearer and nearer to the female. Now she dashes towards him, while he, raising his first pair of legs, extends them upwards and forwards as if to hold her off, but withal slowly retreats. Again and again he circles from side to side, she gazing towards him in a softer mood, evidently admiring the grace of his antics. This is repeated until we have counted one hundred and eleven circles made by the ardent little male. Now he approaches nearer and nearer, and when almost within reach whirls madly around and around her, she joining and whirling with him in a giddy maze. Again he falls back and resumes his semicircular motions with his body tilted over; she, all excitement, lowers her head and raises her body so that it is almost vertical; both draw nearer; she moves slowly under him, he crawling over her head, and the mating is accomplished. After they have paired once the preliminary courtship is not so long. On one occasion a female was the more eager of the two, but this is evidently very exceptional. The female always watches the antics of the