30 RADIOGENESIS IN EVOLUTION. 



the inherited sviccession of phiinage may he intenujjted at 

 the will of the experimenter.* In the summary of the 

 Horn Expedition. Baldwin Spencer notes the varying sizes 

 of mature specimens of the smaller marsupials, especially 

 Phascologale cridicauda, found in the central district of 

 Australia. In good seasons large specimens were found, 

 but during the series of bad seasons and dearth of food, 

 the animals secured were much smaller. f Do we not see 

 here a diminutive form in process of evolution I If certain 

 forms are dwarfed through partial starvation, the result 

 is very obvious in the life of the individual, and this may l)e 

 intensified in offspring subjected to the same conditions, 

 whether the principle of natural selection operate or not. 

 Perhaps such diminutive forms as the Shetland cattle and 

 ponies may here be given as an island parallel to arid 

 conditions in continental areas. To take a wider outlook, 

 there is indubitable evidence that the known history of 

 the Marsupialia in Australia is mainly a record of the 

 survival of relatively small forms, whilst the larger mono- 

 tremes, \: jmbats, kangaroos and ])oly])rotodonts. to say 

 nothing of the giant Diprotodon and Nolotherium, have 

 died out. This has been a concomitant of the gradual 

 change froai more exuberant conditions of the Pleistocene 

 period. 



In contradistinction to Loeb. the most distinguished 

 representative of the vitalist school — Bergson. claims that 

 variations cannot be explained as mere mechanical response 

 to stimuli, but spring from an internal creative impulse. 

 Here may be added Ray Lankester's timely reminder that 

 ■' variation is a common attribute of many natural sub- 

 stances of which living matter is only one. "J Even 

 Astronomy furnishes an example, for has not Saturn a 

 satellite which goes round " the wrong way " ! 



Of exceptional interest is the work done by Karl 

 Pearson, who in his " Grammar of Science " has accumu- 

 lated a multitude of observations on heredity and variation 

 largely with reference to the ])roblems of humanity itself. 



*" Zoologica," Feb., 1914. 



tHorn Expedition, PI. I., p. 143. 



J" .Science from an Easy Chair," Ser. I., p. 3o. 



