1906.] OF MONKEYS IN THE MENAGERIE. 559 



Needless to add, this is hardly the classification to be expected 

 on a priori grounds from the usually accepted views of the affinities 

 of the species concerned. It seems to me to be probable that the 

 swelling will be found to be characteristic of all the species of 

 Mangabeys and Baboons ; but in the case of the Macaques no 

 generalisations can be drawn until further observations have been 

 made. In 1904 I recollect seeing in the Berlin Gardens a female 

 Macaque of a species whose name I have now forgotten, with the 

 swelling like that of M. nemestrinus. Thus at least two species 

 of this genus fall under section a of the above-given table. On 

 the other hand, it is by no means certain that all the forms 

 related to rhesus and fascatus can be ranged with these species 

 under section a . For example, P. L. Sclater (P.Z.S. 1864, p. 710) 

 says that a female of the Formosan Macaque (if. cyclopis) upon 

 reaching matiirity " acquired a most extraordinary development 

 of the parts surrounding the oi-gans of generation." The figure 

 that accompanies this description, however, shows a long lobate 

 swelling extending on each side down the back of the thigh and 

 along the proximal third of the tail — a development quite unlike 

 anything known to me in other species. It is significant, too, 

 that Sclater speaks of this swelling as if it were permanent and 

 not periodic. If permanent the development must probably be of 

 a difierent kind from that now under discussion. If periodic and 

 connected with menstruation it must indicate an important 

 physiological dififei-ence between M. cyclopis and M. rhesus, two 

 species structurally somewhat nearly related. 



The swelling may be nothing but a useless correlative or 

 accompaniment of the physiological processes incidental to men- 

 struation. But, in my opinion, the development of a highly 

 vascular, sensitive, and thin-skinned outgrowth of this nature — 

 an obvious inconvenience to the monkey, since it involves special 

 precautions to prevent injury, impairs activity, and is liable to 

 laceration when quarrels arise — probably, rather than otherwise, 

 carries with it some compensating advantage to the species. 

 What may this be ? Possibly the following considerations may 

 throw some light on the subject. The similarity in form and 

 colour between male and female Monkeys leaves no clue to the 

 sex of a particular individual when seen at a distance. The 

 males, moreover, are not apprised by the sense of smell of the 

 condition of the females when "on heat" as are the males of 

 Carnivora, Ungulata, Rodentia, and of other orders of Mammals. 

 Hence it may be that the function of the swelling in question is 

 to serve as a source of information to the males on the two points 

 mentioned above. I think it may be claimed that such information 

 is of use for the maintenance of the species. But whether the 

 usefulness in these particulars of the swelling be or be not the 

 factor that has guided its evolution, it is difficult to see how such 

 a coloured excrescence can fail to convey the said information in 

 the case of animals so intelligent and keen-sighted as Monkevs. 

 For, as is fully attested by flowers like scarlet geraniums and by 

 Proc. ZooL. See— 1906, No.XXXVIIT. 38 



