492 THE CHANGING WORLD 



consists not so much in protective envelopes of one kind and another, 

 that must inevitably be crushed, as in the development of easily per- 

 meable tissues through which the pressure is equalized. 



Light is essential to photosynthetic plants. These exhibit many 

 adaptations by way of the arrangement and form of their leaves to 

 secure adequate exposure to light. There are many kinds of animals 

 on the other hand, Uke cave-dwellers and deep-sea forms, as well as 

 fungi among plants, that can dispense with light entirely. In such 

 animals, the eyes and other adaptations to a world of light and shadow 

 are either entirely wanting or have become degenerate. To com- 

 pensate animals that live in darkness for their loss of light, tactile 

 devices of various sorts develop, enabling them to find their food 

 and to accomplish the business of living, while in the case of plants 

 the saprophytic method of living a chlorophyll-less life is adopted. 



The reflex mechanism in the iris of the eye by which the size of 

 the pupil is made to vary and the amount of light admitted to the ret- 

 ina is regulated is a beautiful adaptation of the organism to amount 

 of light. In fact, the whole vertebrate eye is an exquisite example of 

 cumulative organic adaptation to the environmental factor of light. 



Biological Adaptations 



The association of organisms with each other gives rise to a great 

 variety of biological adaptations, such as symbiosis, commensalism, 

 saprophytism, parasitism, gregariousness, and social life. 



Flowering plants evolve ways of attracting the visits of insects 

 and of inveigling them to transfer pollen in the production of seeds. 

 Insects in turn are so modified as to take advantage of what the 

 flowering plants offer them by way of nectar and other desirable 

 forms of food. It is significant that flowering plants did not develop 

 in geological time until after insects appeared. 



Carnivorous hunters are fitted to pursue their prey, and the hunted, 

 by developing speed in flight or by wits with which to outguess the 

 pursuer, are adapted to escape. Mother Nature impartially gives 

 both the hunter and the hunted a sporting chance. 



Through protective coloration and camouflage, by bluffing with 

 warning colors, or by intimidating behavior, some animals escape 

 their enemies, while others are blackmailed into surrendering to their 

 captors a part of themselves and escaping with a viable residue, 

 having in reserve the adaptive resource of regeneration of lost parts. 



There is a curious European toad, Bombinator igneus by name. 



