EEACTIONS OF LAND ISOPODS TO LIGHT 231 



According to the experiments, the behavior of PorcelHo ap- 

 pears to be somewhat modified by external conditions. These 

 animals were less negative after living in a dry atmosphere, 

 after exposure to strong light, and when exposed successively to 

 different intensities. The most striking result was a reversal 

 to positiveness which occurred in certain individuals after ex- 

 posure to strong light (fig. 10, table 9). 



As was shown in the preceding section, the normal phototaxis 

 of Porcellio shows a great amount of variation, and hence it is 

 difficult to say to what extent these modifications are actually 

 due to the external conditions of the experiments. 



VI. DISCUSSION 

 A. ECOLOGICAL ANALYSIS 



Ecology is the study of the relation between organisms and 

 their environment. Ecological studies deal both with the dis- 

 tribution of animals and plants and with adaptation, which 

 may be defined as the sum of the structural and functional 

 methods by which the organism is fitted to its environment. 

 The word adaptation is used without implying any theory as 

 to the cause of adaptation. Inasmuch as the present emphasis 

 of studies in animal and plant ecology is particularly on adapta- 

 tions of a physiological nature, the study of animal behavior 

 has become of increasing ecological importance. 



One of the essential distinctions between structure and be- 

 havior is that structure, in the main, is dependent on genetic 

 relationships, while behavior is closely related to the nature of 

 the environment. Without attempting to settle the problem 

 whether environment is the cause of behavior, the facts remain 

 that animals of various structures tend to have the same behavior, 

 if they occupy the same environment (Shelf ord, '14, '16) and 

 that individuals of a single species from different environments 

 often have a difference in behavior corresponding to the environ- 

 ment (Allee, '12, '14; Adams, '15). A particular plan of struc- 

 ture may be suited to a wide variation in environment, pro- 

 vided that the behavior of the animal varies accordmg to the 



