540 DU. p. CHALMERS MITCHELL OX LONGEVITY AND 



a warmed house, and considerable numbers of individuals in an 

 aviary or enclosure giving room for exercise, and access to the open 

 air. Now although many birds can be kept together, and are kept 

 together, many casualties occur. A good deal of fighting and 

 bullying tnkes place, and in practice, it is extraordinaiily ditficult 

 to secure that every bird in the collection gets its due share of 

 food, and is not vs^orried by its messmates. Moreover, there is 

 special danger of individuals which are aifected by a communi- 

 cable disease, or by parasites, infecting their healthy neighbours. 

 Birds in separate cages avoid these evils; they are safe from 

 bullying, they are properly fed, and if they are out of condition 

 temporarily, have a chance of recovery. If we discovint the very 

 considerable advantage of protection tliat the Parrots obtained 

 from their housing in separate cnges, it will be seen from com- 

 parison of their average durations with their known high specific 

 longevity, how poorly the device of keeping them in a heated 

 house has answered. In a majority of cases, birds that have had 

 free access to open air have lived in communities, a,nd before 

 judging of the advantage of fresh aii', we have to discount the 

 perils arising from their communal life. With these limitations 

 and corrections, I think it is as clear an inference in the case of 

 birds as in that of mammals, that making protection from 

 tempei-ature more impoilant than the access to fresh air has 

 failed in j^ractice. 



General Summary. 



(1) This memoir brings together the records of the duration of 

 life in captivity of over 20,000 individual mammals and birds, and 

 contains inforriiation which, so far as I can ascertain, has never 

 before been set out systematically. The individual facts are 

 imperfect, inasmuch as the sources did not record the age, or 

 condition, of the individuals at the time of their reception in the 

 Collection. The probable eflfect of these imperfections is to lower 

 the figures both of average and of maximum duration. I hope to 

 have shewn that from the point of view of exact knowledge and 

 for pi'actical reasons, it is important that those in charge of living 

 animaJs should take steps to record such information as exactly 

 as possible. Every individual should be observed for some time 

 after its arrival, and the date when it is passed into the geneiul 

 collection as apparently in good condition should be recorded, 

 whilst, if the exa,ct age be luiknown, it should be classified as 

 infantile, adult, or aged,. The houses, enclosures, or general con- 

 ditions under which it is kept, with the date and nature of any 

 changes of these, should be recorded. Finally the date, cause of 

 death, and any further notes as to age should be enteied. "With 

 such a system, in course of time, very exact conclusions could 

 be obtained as to the viability a.nd longevity of difierent kinds 

 of animals, and as to the effect of the modes of keeping them in 

 captivity. 



(2) Following Ray Lankester, I distinguish between potential 



