448 DR. p. CHALMERS MITCHELL ON LONGEVITY AND 



observations. Throughout the period in question, these animals 

 were kept in a badly ventilated house, usually kept hot. 



MURID^ No. of Av. duv. Max. dur. 



Indiv. in months. in months. 



HT/di^omyschrpsogaster (Golden-hellled 6 11 17 



Beaver-rat). 



Gerhillus^ whole genus 179 19 54 



G. cegyptius (Lesser Egyptian 39 9 42 



Gerbille). 



G.campestris (Field Gerbille) 2 32-5 36 



G. inclicihs (Indian ,, 15 17 32 



G. longifrons (Long-fronted Gerbille) 79 18-8 54 



(x. jo?/^ar(7^6S (White-rumped ,, ) 2 17 28 



6^. joyramirfztm (Large Egyptian ,, ) 14 14 24 



G. rohustits (Robust ,, ) 2 12 16 



G. shawi (Shaw's „ ) 26 18-8 35 



Psammoinys obesus (Fat Sand-Rat) .1 17 17 



Georychus capensis (Cape Mole-Rat) .1 11 11 



Cricetus finmientarius (Common 12 17 27 



Hamster). 



Cricetomys gambianus (Gambian 8 20 33 

 Pouched Rat). 



Mt(,s, whole genus 64 16 50 



If. arboricola (Sydney Bush- Rat) ... 3 45 50 



M. bcmdicota (Bsmdicoot Jisit) 2 19*5 21 



M.barbarus (Barbary Mouse) 20 19-5 33 



M. blanfordi (BlemioixYs Hat) 3 5 8 



M. cervicolor (Fawn-coloured Mouse) 2 13*5 18 



M. exulans (Pacific Mouse) 9 3"6 7 



M. mimUus (Harvest Mouse) 10 15*5 33 



M.ratttos (Black Rat) 13 17 41 



M. sylvaticus (Long -tailed Field- 2 4*5 7 



Mouse). 



Isomys variegatas (Varied Field-Rat) 7 52 81 



Acomys huiiteri (Hunter's Spiny 11 38'4 53 



Mouse). 



Ar vicola, •w\io\e genns 14 8 25 



A. agrestis (Short-tailed Yole) 7 8^3 25 



A . amj^hibius (Water Vole) 5 9 16 



A. pratensis (Bank Vole) 2 7*5 14 



Myodesleini^iusi^oYwegiainJjernxmxig) 5 5 19 



Fiber zibethicits (Musquash) 7 14 75 



The only published statement regarding the age of mice with 

 which I am acquainted, is MetchnikofF's assignment of "five or 

 six " years as their limit. It may be supposed that the larger 

 forms have a higher potential longevity. The maximum duration 

 in the record is nearly 7 years in the case of an Egyptian Field 

 Rat. Comparatively few of the maxima approach this figure, and 

 the relation between the maximum and average durations is fairly 



