THE RELATION OP INSTITUTIONS TO ENVIRONMENT. 703 



is under these favorable conditions that the potency of heredity is most 

 conspicuous, since the organisms are not fain, as elsewhere and other- 

 time, to expend energy in shaping themselves to their surroundings. 



The fertility of organisms in adaptive devices whereby they are fitted 

 to adverse conditions of environment, shown clearly in the desert flora, 

 is illustrated still more strikingly by certain insects. The walking 

 sticks, the flying leaves, and a variety of creeping and leaping and 

 winging insects adjust form and color to the vegetation on which they 

 habitually rest so closely as to deceive enemies; stingless flies mimic 

 the appearance and habits of stinging wasps and odorless insects 

 counterfeit odoriferous bugs that they may escape molestation ; and in 

 many other ways insect species modify themselves for their own benefit 

 under adverse conditions. The unrelated desert plants grow alike 

 toward tkorniness, waxiness, leaflessness, etc., to meet common needs, 

 and thereby hereditary features are masked; but in insect mimicry the 

 impress of heredity is lost and characters produced through direct 

 interaction with environment replace legitimate features expressing 

 biotic relation. Thereby the exceeding plasticity of the organism is 

 displayed — a plasticity so perfect as almost to suggest that the initial 

 force operating through heredity is as nothing, and that environmental 

 interaction is as everything, in shaping the course of the vital stream. 



The forest, the scant flora of the desert, the redundant vitality of 

 species chancing to outstrip competitors, insect mimicry, all illustrate 

 the potency of environment in determining the career of organisms 

 considered as units, and indicate that primary characters are largely 

 or perhaps wholly subordinate to derived organic characters produced 

 by interaction with the external; and even when the organism is viewed 

 as an aggregation of organs the same lesson may be read. The func- 

 tionless splint bones of the horse are vestiges of digits which were useful 

 organs in equine ancestors, as shown by the joint evidence of paleon 

 tology, embryology, and reversion; the function less and troublesome 

 vermiform appendix is shown by Lucas to be a vestige of a supplemental 

 stomach useful to an herbivorous progenitor, but useless through sev- 

 eral later stages of development ; the feeble vestigial muscle by which 

 one man in a thousand, and one infant in a hundred, is able to move 

 his ear is an all but functionless organ, weakened and nearly lost 

 through disuse; and the dozen or more vestigial structures known in 

 man and the scores known in other organisms are but moribund war- 

 riors in the strife for existence, thrown out of rank and trampled over 

 because of unfitness for battle against the great external — they may 

 boast long lineage and noble station in the earlier stages of organic 

 development, yet their past counts for nought in that ceaseless struggle 

 in which activity is life and inactivity is death. So among organs as 

 among organisms, many fall behind and are lost in the race for con- 

 tinued existence, and it is environmental relation rather than original 

 character that makes for perpetuity. 



