ANIMALS AS PASSIVE MEMBERS (COACTEES) 131 



variety of modifications. Though much rarer, flower clusters and even 

 individual flowers exhibit some of the more striking transformations. 



In exceptional cases where the number of shoots, leaves, or flowers 

 is increased, a certain degree of mutualism appears to enter, but this 

 is more apparent than real, since such parts are rarely quite normal 

 in functioning. Nearly always, the relation is one of pure parasitism, 

 the gall providing both food and shelter for the young of the coactor, 

 regularly with some slight or even considerable disadvantage to the 

 host plant. This rarely has decisive significance, though there may 

 be a minor effect upon the competition between individuals or species, 

 especially when flower and seed production are diminished. 



Invertebrate Omnivores. As has been pointed out elsewhere, the 

 tendency is for animals to select a wide variety of food from the great 

 diversity present in most habitats. Even in the predaceous beetles, a 

 number prove to be plant eaters in part. Forbes (1883, b) made an 

 exceptionally thorough analysis of the contents of the alimentary tract 

 of common genera of carabids and coccinellids and found them to be 

 more vegetarian than ordinarily supposed (Webster, 1880). Of the 

 20 genera of ground beetles studied, 8 preferred a diet more than half 

 vegetable, while in Harpalus the percentage rose to 88 and in 

 Amphasia to 97. For the ladybugs, 2 genera fed exclusively on plant 

 material under certain conditions, while the general range was from a 

 half to three-fourths. An unexpected result was the increase in plant 

 food taken in the midst of an infestation of chinchbugs, but this was 

 chiefly due to the concomitant abundance of fungus spores. 



ANIMALS AS PASSIVE MEMBERS (COACTEES) 



In the general sense of the term, carnivorous animals appear in 

 all classes and embrace a large majority of the orders among mam- 

 mals. They comprise more than half the families of terrestrial birds, 

 most of the snakes, lizards, and amphibians, and a vast number of 

 insect families, especially if larval coactions are taken into account. 

 The animal-eaters fall into two major divisions, carnivores proper and 

 insectivores, while many omnivores are carnivorous by preference 

 when the food supply permits. 



The carnivorous habit has led to certain related coactions which 

 may be regarded as offensive or defensive. These may pertain to the 

 individual or the group; in the one case they usually arise out of the 

 structure of the species concerned, in the other from some social habit, 

 especially cooperation. Read (1920) has advanced the idea that hunt- 

 ing in packs was the first social organization of primitive man. He 



