ARTHROPODA 2QI 



work of the colony, or of other animals (aphides) for the purpose 

 of feeding on their secretions. A high order of social instincts 

 and skill is shown by certain members of this group, the 

 highest, apparently, shown by any of the invertebrate animals. 



333. Behavior. In the Arthropods we are dealing with 

 organisms more complex in their nervous organization and with 

 a greater variety of sense organs than we have yet found, 

 with the possible exception of some of the cephalopods. Their 

 reactions to stimuli and general behavior in the presence of the 

 conditions of life, and probably their mental life, are correspond- 

 ingly rich and varied. We feel that their activities are reflex 

 and instinctive rather than intelligent, although it has been 

 definitely shown by experiment that the crayfish and some of 

 the insects learn to accomplish things by the trial and error 

 method. That is, they modify behavior through experience. 



The nervous system, scattered as it is largely through the 

 segments of the body, is suited more to reflex activities than to 

 intelligent activities. The latter become more pronounced as 

 the brain comes to contain a larger portion of the nervous 

 matter, with more complex connections. 



Crayfish prefer darkness and are positively thigmotropic 

 (that is, like to touch solid objects). Both these reactions are 

 valuable in bringing them into hiding. 



Some species of insects show striking powers of recognizing 

 one another, and of communicating their mental states. This is 

 done apparently through tactile and chemical sense organs in 

 the antennae and other appendages and by the making and 

 hearing of sounds. The whirring and buzzing of wings in flies 

 and bees and mosquitoes, the scraping of legs and wings by which 

 chirping is done, the sustained stridulations of the cicada are 

 examples of these. The lazy hum of the bee is very different 

 from the angry buzz, and is quickly recognized by other mem- 

 bers of the hive. In others as the mosquito the song of the 

 female is probably a sex call. Probably many of them, such 

 as the tappings of some beetles, are without meaning except as 

 evidences of nervous activity. Others are merely incidental to 

 necessary activities, as flying. 



