VOL. VIII.] RELATIONS OF BIRD-DISTRIBUTION. 35 



the more primitive environment, from A\hich other 

 environmental adjustments are more recent adaptations 

 (and possible lines of racial extension), and adaptation 

 will tend to proceed through food-adjustment to breeding- 

 habitat adjustment. 



It may be assumed that the phenomenon of racial 

 structural history illustrated during the development of 

 the individual, is paralleled, within limits, by fimctional 

 characters, and so far as this parallelism holds good, it 

 may be expected that a recapitulation of the racial 

 environmental history will in some degree reach fimctional 

 expression in the individual. If the individual resumes 

 M'ithin its life-time the racial environmental history, then 

 the nesting-environment is the more primitive. The 

 present environmental '' requisites " of the young repre- 

 sent the ancestral environmental " requisites " of the race. 

 Is it permissible to go a step further and to compare 

 the functional character which takes the form of a 

 breeding habitat bias, Avith those structural vestiges which 

 are the reflection of past history rather than adjustments 

 to present conditions ? 



Outside birds, the environmental restriction ascribable 

 to the conservatism of the breeding-habits is illustrated 

 in terrestrial animals Mith aquatic larvse ; in the salmon 

 which procures its food from the sea, but must repair 

 to fresh w ater to breed ; in the eel which passes its life 

 in fresh \\ater, but must go to the sea to lay its eggs. 

 Is it unreasonable to assume that the Curlew which feeds 

 on the shore outside the breeding-season, but must go 

 to the hills to nest ; the Goldcrest which is at home in 

 deciduous woods in winter, but is practically confined to 

 coniferous woods in summer ; the Golden Plover able to 

 derive sustenance from cultivated land, but nesting only 

 on moors — may represent analogous, if less extreme, 

 instances ? The habitat wherein breeding is accomplished 

 is the most primitive environment. " The key to the 

 present lies in the past." The bird's present distribution 

 is based on, and limited by, a breeding-habitat, the type 

 of \\'hich is fixed by ancestral experience, modified only 

 in subordinate degree by present conditions. As racial 

 history determines present structure, so in like manner 

 racial environmental relations appear in present habitat 

 preference. In a sense the bird inherits its environment. 

 Present poAver of adaptation and modification is inverse 

 to the duration and narroAAness of racial experience. 

 Environmental stabilization leads to faunal stabilization ; 



