The Courtship of Animals

by W. P. Pycraft

Mention of numerous cases has already been made where the female is larger than the male, and is the more pugnacious, and in such cases the females are generally more numerous than the males. Some of the deep-sea Prawns exhibit the same peculiarity. And in these the sword-like forward prolongation of the head-shield is far larger than in the male. Now this rostrum is the most formidable weapon which the Prawn possesses, so that we may, with tolerable certainty, conclude that the females fight their rivals for the possession of the males, which are, in these species, far less numerous than the females.

Among the lower Crustacea, such as the “Fairy-shrimps,” “Brine-shrimps,” the “Water-fleas,” and the “Copepoda,” which play so important a part in furnishing food for many of the fishes which in turn feed us, secondary sexual characters of an extremely interesting kind are met with. These, however, are never such as appeal to the eye, for the vision in these creatures is but feebly developed. Scent, as is usual where sight is defective, plays an important part in enabling the sexes to discover one another. Selection here secures success only to such as have the proper odour and the most sensitive organs of smell. In these creatures, as with the butterflies and moths, the odour emanating from the female is most powerful, while the sense of smell is most developed in the male. One of the most striking illustrations of these facts is furnished by that very beautiful species Leptodora hyalina—a veritable giant among these small Crustacea—wherein the antennæ of the male are produced into enormously elongated comb-like structures, the teeth of the comb being formed by delicate olfactory filaments. In the female these antennæ are extremely short and their olfactory filaments are limited to a small terminal tuft to the antennæ, answering to the larger tuft at the base of the comb of the male.

To the majority of species, however, delicate odours seem to make little or no appeal, since excessive development of the olfactory apparatus, such as is seen in the aberrant Water-flea (Leptodora), is rare. This is perhaps explained by the fact that Leptodora is a species which does not herd together in vast numbers, hence, probably, the need of some exceptional means whereby the males may discover the whereabouts of the females, while in the case of the swarming hosts formed by Water-fleas and Brine-shrimps, for example, no such highly specialized aid is necessary. Instead, the males have developed powerful arms for the capture and retention of the females. In the case of the Brine-shrimp these arms are of quite formidable proportions. The males of the Copepoda, remarks Weismann, “possess on their anterior antennæ an arrangement which enables them to throw a long, whip-like structure like a lasso round the head of the female as she rapidly swims away. The antennæ of the male Daphnids, too, are in one genus (Moina) developed into a grasping apparatus; ... the first antennæ ... are not only much longer and stronger than those of the female, but they are also armed with claws at the end, so that the males can catch their mates as with a fork, and hold them fast. And even that was not enough, for, in addition, the males of most Daphnids possess a sickle-shaped but blunt claw on the first pair of legs, which enables them to cling to the smooth shell of the female, and to clamber up on to it to get into the proper position for copulation.

Plate 40.

SOME REMARKABLE DEVICES.

1. A Water-flea (Moina rectirostris): male showing the claspers-the front pair of “legs,” for grasping the female.

2. The female of the same, in which the “claspers” appear as mere stumps.

3. The aberrant Water-flea (Leptodora kindlii): the male showing the long comb-like antenna for the discovery of the female (the left only is drawn), and the female, just beneath, lacking this olfactory organ.

4. An extraordinary species of Bug in which the upper surface of the thorax has been produced backwards to form an overhanging pent-house, of unknown function, and illustrating the theory of “Hypertely.”