These facts are the more interesting when contrasted with what obtains among other fighting species which must woo the females. Take the case of the common freshwater Stickle-back. In this species the body is invested with an armature of bony plates and spines in place of scales, while the males are arrayed in vivid hues of red and blue. Any survey, however, of the reproductive activities of this little fish must take into account certain quite remarkable prenuptial actions and instincts. Briefly, before the male commences his search for a mate he constructs a nest of fine fragments of aquatic weeds, which are held together, not by interweaving as with birds’ nests, but by a sticky and copious secretion from the kidneys. According to some authorities, this secretion is to be regarded as a pathological product caused by the undue pressure of the ripening testes. It is difficult to accept this interpretation, for it might with as much reason be argued that the copious secretions of the salivary glands of the edible Swift—which builds a nest constructed entirely of hardened saliva—are also pathological in character. But be this as it may, the nest completed, the male seeks a mate, or mates, for polygamy is the rule of his tribe. In his search for these he has constantly to do battle with other males, whom he endeavours to disembowl by swift rushes contrived to t rip open his rival as he passes, by means of one or other of the erectile spines which project from his back and belly. With the females whom he desires he uses the arts of peaceful persuasion, swimming backwards and forwards before her in his endeavour to excite her amorous instincts. At last he persuades her to enter his bower and deposit a few eggs, fertilizing them immediately they are laid. The first to enter leaves by forcing a passage through the opposite wall of the nest, a happy contrivance, for thereby a current of water can be constantly driven through, leaving fresh oxygen to the developing eggs. One female after another is inveigled into the bower, until the complement of eggs is complete. These, singularly enough, are now taken charge of by the male. He it is who creates life-sustaining currents which bathe the eggs, by the rapid vibrations of his breast-fins, and he it is who protects them from their most persistent enemies—the females who laid them. As soon as the fry appear the duties of the male are still further increased. He must guard them from their mothers, and other foes, and he must prevent their too extensive wanderings. Such as stray too far afield are sucked into the mouth and brought back again to the nursery, where they are set at liberty by a reversal of the sucking action. That the male of a polygamous species, and with all the attributes of a polygamous species—pugnacity and vivid coloration—should take upon himself the duties which under like circumstances among the higher vertebrates are undertaken by the female is a very remarkable and puzzling feature.