RELATIVE VIABILITY IX MAMMALS AND BIRDS. 435 



With the exception of the Loris and the Potto, the Lemurs 

 show a longer average duration and a higher maximum duration 

 than in the case of Monkeys. Tliere still remains, however, a 

 very marked discrepancy between the aver;ige duration and the 

 maximum duration, although the latter must be regarded as much 

 below the probable potential longevity. On the whole, lemurs 

 have been kept under conditions not very different from those of 

 the monkeys. It is probably in their favour that as they are 

 more nocturnal than monkeys, they have escaped to a greater 

 extent erroneous feeding by the public, whilst as they are on the 

 whole more strictly arboreal than monkeys, the relative absence 

 of light and the more equable temperature in the interior of 

 warmed houses have not been so damaging to them. On the 

 other hand, they are, on the average, sina,ller than monkeys, and 

 as within the same group smaller animals have usually shorter 

 lives than larger animals, a longer average duration and a 

 higher maximum duration as compared with monkeys, was not to 

 be expected. 



Sii,mmary of Quadrumana. 



It is well known that the higher races of men have a hioher 

 viability than the lower races ; that is to say, they display a 

 greater power of resistance to adverse conditions, to changed 

 conditions, and to diseases (although not necessarily to any 

 particular disease). It is of interest to find that a still lower 

 viability is exhibited by apes and monkeys which as a group 

 have an amazingly poor power of resistance to the adverse con- 

 ditions of captivity. It is even more interesting to note that 

 there is a marked gap between monkeys and lemurs in this respect. 

 The fact that the latter on an average live four or fi\e times 

 as long in captivity as monkeys, shows a marked difference in their 

 constitutions. I may recall a curious by-product of an investi- 

 gation into the feeding of snakes made by my friend and colleague 

 Mr. R. 1. Pocock and myself (P. Z. S. 1907, p. 785), when we found 

 that lemui-s difiered fiom monkeys in having no fear of snakes. 

 Fundamental differences between groups are revealed not only by 

 anatomical characters, and in view of the present tendency to lay 

 increasing stress on the anatomical links between lemurs and other 

 primates, I think their physiological differences are worth some 

 attention. There is, however, another interpretation of the 

 higher viability of lemurs in captivity. The close affinity of man 

 and monkeys may render the latter more subject to human diseases 

 and therefore more liable to suffer from the vicinity of man. Such 

 a question can be answered only by long records of the causes of 

 mortality based on adequate diagnosis. The laboi'ious woi-k of 

 ray friend and colleague Mr. H. G. Plimmer, unfortunately does 

 not extend back to the period with which my present inquiry deals. 



Even if it be accepted that apes, monkeys, and lemurs are 

 creatures of inherently low powers of resistance, the striking 

 difference between the average durations and the maximum 



