FUNCTION AND ENVIRONMENT 193 



our science, paralyzed its thinkers, some- 

 times even skeletonized or mummified them. 

 There is an endless diversity in environments, 

 and some of them are most extraordinary 

 the iceberg, the hot spring, the mountain top, 

 the abysses of the ocean, the cave, the in- 

 terior of another creature but_Jor_ p.ach 

 kJTH of ore*" 11 '* *h> iff a,n indispensable 

 minimum of fflippHpjg.fl.TiH influences, apart 

 from which it cannot develop, or grow, or 

 continue to live. This is 



of livipg tTn'nggj that, nf pnnst.fl.nt. 



(2) But surroundings 

 t.np 



many cases, where the external changes are 



regularly recurrent, like seasons and tides, 



the organism falls into step with them; so \ 



that there are internal rhythms, punctuated 



by external periodicities. The latter may 



come to be needed only as the liberating 



stimuli, or trigger-pullers, of the former. 



/Experiments show that some young tropical 



/ acacias are hereditarily wound up, as it 



were, to a twelve hours' day and night 



times of leaf-expansion and leaf-closure. 



The cold of winter is probably the stimulus 



rather than the efficient cause of the brown 



x stoat becoming the white ermine. 



(3) To some of the irregular changes in its 



