It is probable that the “bloody sweat,” which at times covers the hide of the Hippopotamus just after leaving the water, is associated with the period of rut. This mysterious exudation is accompanied by small crystals; but though red in colour, it contains no blood. So far no reasonable explanation for this remarkable phenomenon has ever been given, but probably it will be found to be associated with the sexual activities and is possibly odoriferous. A precisely similar exudation occurs in the neck of the male of the Red Kangaroo. That these secretions play an important and perhaps variable part in the selection of mates seems demonstrated in the case of an incident related to me by my friend Mr. John Cooke, who some time ago was watching a flock of some three hundred sheep while it was being driven by the shepherd and his dogs into a field. As soon as they were securely shut in, and the shepherd had gone, three rams who were included in the flock at once began a three-cornered fight. One, presumably the youngest, was soon vanquished. The other two soon settled their differences, and the clashing of horns was at once followed by a very different performance. The master ram began to run in and out among the ewes, sniffing at each, and driving out those whose odour most pleased him. Having at last satisfied himself with a harem of about one hundred, the second ram was allowed to make a like choice, and behaved in a like manner, leaving the remainder to the ram which was first vanquished. May we take it that the strongest and oldest rams selected the youngest ewes, and the oldest were left to the youngest, and first conquered ram? By some such rough and ready method of selection Nature may contrive that the immature male shall do as little harm to the race as possible by mating with the oldest, and in many cases barren females. Our survey of the “hoofed” animals has so far been confined to the ruminants. Space must now be found for a brief review of what obtains under like circumstances in the case of the great pachyderms—the Elephant, Rhinoceros and Hippopotamus; the Pig and the Camel. [Illustration: Plate 9. _Photo by Lord Delamere, from “The Living Animals of the World”_ ELEPHANTS. The sexes differ but little in general appearance: and chiefly in the superior size of the male and his more massive tusks. [Face page 70.]