184 HABIT AND INTELLIGENCE. [chap. 



Change o. from such a cliange of climate as we know from geological 

 c ima e. evidence to have taken place in past ages/ or from the 

 animal being transported by man and becoming wild in 

 its new abode, or from spontaneous migration; and it is 

 sometimes impossible to say what determines the migra- 

 tions of animals. In such a case, as already remarked, the 

 animal, if it becomes adapted to the new climate at all, and 

 is not destroyed by it, may become adapted by acquiring 

 either the passive habit of disregarding the cold, or the 

 active habit of producing warm fur on its skin. Of passive 

 habits I need say no more ; but the subject of the forma- 

 tion of active habits, inckiding formative ones, to meet 

 new circumstances of life, is practically an infinite one. 

 Suppose another instance of the same kind. In conse- 

 Chauge of quence of the migrations of the animals that serve as its 

 food, a beast or bird of prey is compelled to change its 

 mode of hunting.^ It may need keener sight, in order to 

 obtain its new prey : in this case, its sight will be more 

 exercised, and will become stronger ; and in the course of 

 some generations, probably, its eyes wiU be enlarged. Or 

 it may need a keener sense of smell : in this case the same 

 changes will be effected in its olfactory organs. Or it may 

 need greater fleetness : in that case the muscles of its legs 

 will become stronger and larger; and, what is most im- 

 portant to observe, such a change as this will directly or 

 indirectly affect the form of every part of the body — partly 



1 I do not mean that there is any proof of a glacial period being one 

 of extreme cold. A cold shimmer would be enough to produce it. 



2 Migrations sometimes occur in very unexpected ways. I extract the 

 following from the Quarterly Journal of Science, October 1864 : — 



" The sudden occurrence of Pallas's sand-grouse {Syr7-Jiapte^ 2^<^'>^<^^oxus) 

 over the greater part of Europe has attracted the attention of ornitholo- 

 gists, and Mr. Alfred Newton has collected infomiation which shows that 

 this remarkable bird, hitherto almost unknown to the European fauna, 

 has been met with during the year 1863 in no less than 148 localities in 

 Europe and Great Britain, tracing the invading host through 33° of longi- 

 tude, from Galicia to Donegal. He regards the proximate cause of this 

 wonderfid movement as the natural overflow of the population of Syrrhajites, 

 resulting from its ordinary increase, being a bird which has comparatively 

 few enemies, while its time of incubation is short in comparison with what 

 it is in most ground-feeding birds." 



The Byrrliaptcs is a native of the strppcs of Central Asia. 



