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About colour, in the Siamang (H. Syndactylus) both sexes (so far as known) are always black. In H. hoolock, the male is always black (according to my considerable experience), the female never so, unless very partially, being of all shades of brown from fulvous-white to fuscous. All have the white frontal band, but more or less broad. (This is another instance of black males & brown females, & I may remark that the Bos or Bubalus brachyceros has a slaty-blue male and a bright chestnut female. Again, the N. American rattle-snake (Crotalus durissus) has the males much darker than in the other sex—vide specimens in Z. G. This is an interesting case, and how about the black examples of Vipera berus?) In Hylobates leuciscus, agilis, and lar, both sexes vary alike in colour, from black to that of a whitish blanket, and I have been told that there are communities of these pale examples of H. lar in the Malayan peninsula, upon which variety is based the H. entilloidis of Is. Geoffroy. Thus we have the Siamang always black, the hoolock black in the male sex only, and other gibbons in which both sexes are alike variable in colouring. When upon a tree the gibbons use the arms only in progressing, swinging with amazing force and speed from tree to tree, and however great that speed, they can stop themselves most abruptly, then resting crouched on the feet and callosities only.— Have you remarked the tendency of hybrids to be larger than the parent species? This is notably the case with hybrid pheasants of the P. colchicus type, which are fertile inter se, as the hybrid between P colchicus & P. versicolor. The linnet and canary mule is always much larger than its parents—