202 APPLICABILITY OF AGE AND AREA [pt. ii 



It was thus becoming gradually clear to me that -with perhaps 

 rather greater deviations than in plants, Age and Area was also 

 a rule for animals, and in the latter half of 1920 I began to write 

 a paper, which I hoped might be published by one of the zoo- 

 logical journals, upon the application of Age and Area to such 

 questions. But as about this time the work upon the "hollow 

 curve," described above, began to show promise of very striking 

 results, I decided that it would be better to leave the matter 

 alone for the meanwhile. 



Since finding that the hollow curve is practically universal in 

 the distribution, and also in the actual evolution, of plants, and 

 that it can be traced by merely adding up, and sorting into sizes, 

 the genera that make up any group, the application of the theory 

 to animals has been rendered a much more simple matter. 

 Professor Stanley Gardiner once more came to my assistance, 

 and gave me a start with the names of reliable catalogues of 

 genera and species, such as those of Boulenger (Lizards, Snakes, 

 Amphibia, Perciform Fish); and ]\Iiss Taylor, Librarian of the 

 Balfour Library, Cambridge, showed me a number of others. 

 Finally, Professor Stanley Gardiner recommended me to apply 

 to Dr Hugh Scott, the Curator in Entomology, and an authority 

 upon the Beetles. With his assistance, which was freely and 

 liberally given, I have been able to enumerate a number of 

 families of this group. 



The result of all these enumerations is to show that the 

 "hollow curve" is as well mnrked in zoology as in botany, for 

 I have found it to sJiow clearly even in such small groups as 

 the lizards and the snakes (fig. on p. 201), and it is as evident 

 in the Ungulate Mammals (Lj'dekker, 1916), the Chiroptera 

 (Anderson, 1912), the Amphipodous Crustacea (Bate, 1862), 

 the Marsupials (Oldfield Thomas, 1888), the Mycetozoa (Lister, 

 1894), and even in such small groups as the Cyclostomatous 

 Polyzoa (Buck, 1875). 



Some of these curves are shown in the fig. on p. 201. As it 

 might be thought that parasitic animals would show a different 

 curve, I counted the Ichneumonidae (de Dalla Torre, Cat. Hijm., 

 1901) upon Dr Scott's suggestion, and the illustration shows 

 that this group also exhibits the hollow curve, though there is 

 one irregularity shown at an earlier stage than usual. There are 

 60 with four species and only 50 with three, whereas the numbers 

 usually do not show much irregularity till one comes down to 

 about 20. 



