i 3 6 BIOLOGY AND ZOOLOGY 



donts; and the Litopterna from the S. American representatives of the Menisco- 

 theriidae. 



The relations of the Cetacea, including the Zeuglodonts, seem to be with the Insecti- 

 vore-Creodont group, but no good evidence of a specially great antiquity of the order, 

 or of relationship with the Marsupials or Pre-Placentals, has been advanced. 



-..-.- : :.. -.-.' >: M'jjir 



Longevity in Mammals and Birds. 



P. Chalmers Mitchell has published an elaborate memoir on longevity in Mammals 

 and Birds (see E. B. xvi, 974 et seq.), with special reference to the viability of these 

 animals in captivity. It is obviously impossible, except in the rarest cases, to obtain 

 information as to the duration of life in wild animals, and therefore enquiry into the 

 duration of life of animals in captivity is the best available means of reaching knowledge 

 as to the relative longevity in different groups, and as to their viability in captivity, or 

 power of resistance to new environment. He examined the records of duration of life 

 in captivity of over 20,000 individual mammals and birds, and has collated and classified 

 these systematically, giving in the case of each species the average duration and the 

 maximum duration, comparing the figures with maxima otherwise known or suspected. 

 He points out, however, that the materials were defective in two important respects, 

 inasmuch as the age and condition of the individuals at the time of their reception were 

 unknown or unnoted. 



Following Sir Ray Lankester, he distinguishes between potential longevity, the limit 

 of age which an individual could reach if placed in the most favourable circumstances, 

 and average or specific longevity, the average age to which the members of a species 

 attain under the natural conditions to which a species has become adapted. The differ- 

 ence between the two is a measure of the severity of the conditions to which the species 

 is subjected. When creatures of closely similar structure are compared, it appears that 

 greater size is generally associated with longer life and higher viability. But the 

 correlation completely fails when animals of different structure are compared; carnivores 

 for instance, in proportion to their size, are much longer lived than herbivores; and, 

 except for ostriches, which resemble herbivorous mammals in many respects, all 

 birds, in proportion to their size, can attain much greater ages than mammals. 



In dealing with animals in captivity, Mitchell replaces the terms " potential longev- 

 ity " and " average longevity " by " maximum duration " and " average duration." 

 He comes to the practical conclusions that the climate to which a captive animal is 

 native has the smallest possible relation with its viability in captivity, and that the idea 

 which has so long governed those who are responsible for captive animals, that it is 

 necessary above all things to protect them from cold, leads to complete failure. Mam- 

 mals and birds not only can endure considerable cold, but are favourably affected by 

 frequent and rapid changes of temperature. In the long list of species that have been 

 kept in captivity, there is no case of even reasonably good viability where the animals 

 have been kept indoors and provided with artificial heat. All the cases of mammals 

 and birds where there has been relative success are those where the creatures either had 

 no artificial heat at all, or had constant access to the open air from their warm shelters. 

 These conclusions are in harmony with the methods which are beginning to find their 

 way into zoological gardens and stock-breeding establishments, but many stubborn 

 prejudices have yet to be conquered. Incidentally Mitchell points out that the presence 

 of parasites has an important bearing on viability. The conditions of small well-heated 

 quarters are most favourable to the preservation of parasites and to the chances of 

 healthy creatures being infected by their neighbours, so that the temperature relations 

 in many cases may act on the viability of animals through the intermediacy of parasites. 



A New Fossil Primate. 



Although no reasonable biologist doubts the descent of man from ape-like ancestors, 

 geological evidence of the actual line of descent is vague and dubious to an extent that 

 almost justifies the existence of the popular phrase " missing link." In 1910 our state 



