No. 571] TERRESTRIAL ASSOCIATIONS 



419 



animals are correlated with all three of these conditions. 

 The characters are both "adaptive" (fixed by heredity), 

 and regulatory (not fixed). 



Following is a synopsis of correlations between the 

 various types of characters and the three conditions of 

 existence, in the relation of the animal to its antagonistic 

 animal environment. 



(I) Characters Which Enable the Animal to Obtain Food 



1. Structural Characters. — Animals of selective food- 

 habits often have specialized structures, as in the case of 

 the long tongue of woodpeckers. Animals of non-selec- 

 tive food-habits have mouthparts that are not so highly 

 specialized ; thus grasshoppers and cutworms have heavy 

 nmndiMes for cutting vegetation; tiger-beetles and 

 Chrysopa larvae have sharp piercing mandibles. The 

 whole structure of the predaceous animal, its "action 

 system," is sometimes suggestive of the manner of pur- 

 suit or holding of its prey. 



2. Physiological Characters. — The physiology of ani- 

 mals of different food-habits differs materially. Physio- 

 logical characters are not apparent, generally speaking, 

 and are secondary to psychological characters. The 

 range of food assimilable by the animal is usually much 

 wider than that selected by it, as is seen when animals of 

 selective habits take new kinds of food when the usual 

 food is exhausted, often thriving seemingly as well as 

 before. 



3. Psychological Characters— Selection of food is 

 determined chiefly by behavior characters of the animal. 

 These may be so widely variable that the animal will be 

 virtually omnivorous, as in the case of crickets, or so 

 narrowly restricted that it eats only a single species of 

 plant or animal, as the leaf -beetle Blepharida, a sand- 

 prairie insect eating leaves of the three-lobed sumac, and 

 the pentatomid bug, Pcrillus, which feeds on Blcpliarirla 

 (cf. E: 49, 30). Selection is only one of the many psycho- 

 logical characters relating to food. The behavior char- 

 acters manifested in obtaining food are of great variety. 



