770 Causes and Course of Organic Evolution 



^ 



has been effected. This also can be traced through successive 

 stages. The migratory locusts live and feed together in enor- 

 mous swarms, and often perform long social journe^dngs in 

 search of food, that much resemble those conducted by bison 

 of the western prairies in former years. The countless myri- 

 ads of individuals, that often represent one species, the prac- 

 tically world-wide distribution of the species and genera, as 

 well as their successful mode of defense against enemies of 

 many kinds, constitute them one of the dominant groups. 

 They are all purely vegetable feeders. 



Under the ancient group of the Neuroptera, the Termites 

 or white ants have advanced to a high degree of social organi- 

 zation. In addition to the carefully preserved males and 

 females, there is a soldier and frequently also a worker caste, 

 the soldiers being usually much larger than the workers. The 

 division of labor shown, the elaborate and often huge nests 

 constructed, the mode of feeding, and the wide distribution 

 of the known species over the world, all indicate that the coop- 

 erative habits evolved have greatly aided them in attaining 

 a dominaut place. The nervous system has been stated to 

 be comparatively simple, but a careful study of these with 

 other individualistic neuropterid genera is greatly to be desired. 



The Hymenoptera is the insect group that preeminently 

 shows cooperative evolution, but which is also suggestive as 

 showing graded transitions from the competitive to the higher 

 state. \^Tiile the chalcid and ichneumon flies are eminently 

 individualistic and carnivorous, others like the saw flies include 

 genera that show marked care for the young, and a certain 

 degree of social union in the formation of cocoons. But in 

 the groups of the wasps and bees some are solitary and com- 

 petitive, others are highly social and cooperative, while still 

 others show transition conditions. 



The ants, however, none of which are solitary, excel these 

 as well as all other insects, and even most vertebrates, in their 

 elaborate cooperative and social organization, as they do in 

 their highly developed nervous system and sensory apparatus. 

 So Lubbock truly wrote: "If we judge animals by their intelli- 



