3*6 Problems of Organic Adaptation 



develops toward the end, or shall we say "for the purpose," 

 of vision, and yet there is no vision until after all these parts 

 are formed and connections have been made with the central 

 nervous system, which does not occur until late in develop- 

 ment, sometimes, as in the case of the rat, some time after 

 birth. Organs are sometimes developed which are used 

 only once in the life of the individual, as, for example, the 

 egg-tooth on the beak of a bird, which is used only for 

 breaking its way out of the shell at hatching. 



In all of its general features development is teleological, 

 and contemplating this we may well appreciate the words 

 of the psalmist, "I am fearfully and wonderfully made." 

 "In thy book all my members were written which in con- 

 tinuance were fashioned when as yet there was none of 

 them." 



5. Adaptive Behavior 



Some of the most striking of all adaptations are found in 

 the field of behavior and instincts. Even the simplest plants 

 and animals avoid injurious regions and substances and find 

 beneficial ones. For example, some bacteria will aggregate 

 in certain regions of the spectrum and avoid other regions; 

 they move away from salt solutions, or from distilled water, 

 and collect in nutritive substances. Paramecium and many 

 other protozoa behave toward injurious or beneficial sub- 

 stances in a similar manner, and especially notable is the way 

 in which Paramecium avoids extremes of heat and cold and 

 remains in regions of moderate temperature. The tropisms 

 of germ-cells, of seeds, seedlings, and embryos, are generally 

 adaptive. In plants as well as in animals the sperm finds the 

 egg and is received by it. The root of the seedling grows 

 down into the soil and the shoot up into the light and air. 

 Sensitive plants close their leaves when stroked or exposed 

 to dry air, thus preventing injury or dessication. Insectivo- 



