All the distinguishing characters of the male which we have hitherto considered have had reference to gaining the favour of the female, but there are many other secondary sexual characters which are employed in quite a different manner to secure possession of the female. I have already mentioned that in many butterflies the males possess a much larger organ of smell. The antennæ of the males of numerous beetles, such as the cockchafer and its relatives, are also much larger, and furnished with much broader accessory branches, than those of the female, and the same is the case in many of the lower crustaceans, like the large transparent Daphnid of our lakes, _Leptodora hyalina_. Here the anterior antenna bears (Fig. 56, _A_ and _B_, _at´_) olfactory filaments; in the female this appendage is small and stump-like, while in the male (_A_) it grows to a long, somewhat curved rod, which is extended obliquely into the water, and in addition to the nine olfactory filaments of the female (_ri_) bears from sixty to ninety more (_ri´_). [Illustration: FIG. 56. _Leptodora hyalina._ _A_, head of the male. _B_, head of the female. _Au_, eye. _g. opt_, optic ganglion. _gh_, brain. _at´_, first antenna with olfactory filaments _ri_ and _ri´_. _sr_, œsophageal nerve-ring. _n_, nerve. _m_, muscles.] In this and many other such cases it is not the struggle of the species for existence which has so markedly augmented this distinctive characteristic of the male; it is undoubtedly the struggle of the males among themselves, their competition for the possession of the females. In regard to decorative distinctions, the reality of a rivalry in wooing and the ultimate victory of the most decorative may perhaps be still doubted; but it is quite certain that, on an average, the male which can smell and track best will also gain possession of the females more easily than one less well equipped. Exactly the same is also true of those cases in which the male distinguishing character does not refer merely to finding the female, but to holding her fast, or, as we may say, to capturing her.