THE EPIC OF EVOLUTION 



489 



The activation upon occasion of the mammary glands, as well as 

 the formation of antitoxins, and the acquisition of immunity to cer- 

 tain disea"ses, are further examples of physiological adaptation to 

 bodily needs. 



Psychological Adaptations 



Patterns of instinctive behavior which adapt an untaught cater- 

 pillar to spin a cocoon of a definite sort, or direct an insect to lay 

 its eggs upon a particular food-plant specific for its offspring which it 

 will never see, as well as the inner urge that causes birds, and certain 

 other animals, to migrate periodically, may possibly be cited as ex- 

 amples of psychological adaptation. At any rate, the exercise of the 

 nervous system that enables actors to repeat their lines unconsciously 

 in dozens of plays, and by which musicians are able upon repetition 

 to perform complicated and extensive scores without conscious effort, 

 comes close to being an adaptation of a psychological nature. 



Genetical Adaptations 



Adaptations frequently work for the benefit of the species rather 

 than for the welfare of the individual. 



The clever dandelion grows close to the ground in a flat rosette. 

 This habit enables it to escape from browsing animals to a consider- 

 able degree and to with- 

 stand trampling. Its yel- 

 low blossom lies low and 

 bides its time until all is 

 ready and then, just at 

 the critical time, the hol- 

 low stem shoots up like a 

 fire ladder into the air 

 almost overnight, bearing 

 a cluster of white-tufted 

 aviating seeds that are 

 all prepared for distribu- 

 tion. They are so deli- 

 cately poised, pincushion- 

 fashion, in their elevated position that the slightest breeze is 

 sufficient to waft them on their way. 



All the many reproductive modifications, both structural and func- 

 tional, which are involved in the fertilization of animal eggs as well 





^ — "€_. 



The adaptable dandelion, providing for itself 

 and for its progeny. 



