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THE AMEBIC AN NATURALIST [Vol. XLYIII 



to surroundings in color or form — all are of advantage to 

 animals which possess them. Certain of the interstitial 

 or blowsand animals resemble in color the sand on which 

 they rest (Cicindela lepida, Stachyocnemis, Psinidia, 

 Spharagemon; cf. E). 



2. Physiological Characters. — Malodorous and ill- 

 tasting animals are to a considerable degree exempt from 

 attack. This is essentially a physiological modification, 

 though a structural basis in the form of glands may be 

 present. In the sand prairie Chrysopa (lace-winged fly), 

 a number of Hemiptera, ladybird beetles, soldier bugs 

 (Cliaidiognatlnis), blister-beetles (Epicauta), and others, 

 are ill-tasting (perhaps not to some animals). The 

 skunk's lack of caution is well known. 



3. Psychological Characters. — Self-preservation in 

 animals depends more upon their activities and behavior 

 than upon special structures. The ordinary methods of 

 resisting or evading attacks of enemies are generally 

 known and need not be discussed. Many specialized in- 

 stincts have arisen, such as feigning death, or dropping 

 to the ground when disturbed, as seen in many herbi- 

 colous beetles. 



4. Biographical Characters. — It is to the advantage of 

 animal species preyed upon by others if their period of 

 greatest abundance is timed with the period of greatest 

 activity of the animals which feed upon them. 



5. Numerical Characters. — Animals, as well as plants, 

 must produce a normal excess in numbers which will pro- 

 vide food for other animals and still leave a sufficient 

 number of individuals to continue the species. 



It will be noted that the various kinds of characters 

 usually accompany . one another, all being parts of a 

 single modification. This modification may have rela- 

 tion to one or to several of the environmental influences 

 (physical, plant or animal) or to more than one kind of 

 antagonistic relation between the animal and others. 

 The modification is not necessarily advantageous to the 

 animal with respect to all or to any features of the 



