Nervous System 127 



locomotion on land and even for climbing. In land gobies there is a 

 tendency to have a broad cleithrum at the base of the fin, the basal 

 bones often fuse; fin rays are short and few; and special muscles 

 develop for walking which are not present or are poorly developed 

 in aquatic gobies. Changes from aquatic to land life involve better 

 muscular development and nervous coordination (Pike, 1924) . 



Nervous System 



As animals have progressed from aquatic to land life, they have 

 attained greater speed in their locomotor responses to stimuli; more 

 dependence has been placed on sense organs which give distant, 

 rather than contact, perception; and more effective mechanisms have 

 been developed for the control of bodily activities. Hormones, 

 which in primitive metazoans are probably produced more or less 

 by cells throughout the body of an animal, come to be secreted by 

 definitely localized organs and are integrated with nervous mech- 

 anisms for the control of bodily functions. 



In the ocean, where small organisms suitable for food float every- 

 where in the water and accumulate as oozes on the bottom, radial 

 symmetry, with its decentralizing influences on nervous organiza- 

 tion, is common. But on land there are no radially symmetrical 

 animals. Terrestrial bilateral types show progressive cephalization 

 and delegation of bodily control to nervous mechanisms, which per- 

 haps have reached their climax in arboreal and aerial animals. 



The eyes of terrestrial arthropods are often very large compared 

 to those of types that live in water (Harms, 1929) and come to 

 constitute a considerable portion of the nervous system (Kennedy, 

 1927a) . The ghost crab, Ocypode, can see objects clearly at dis- 

 tances of 10 to 15 meters (Harms, 1929). The compound eye of 

 an agile insect predator, such as a dragon-fly or a robber-fly, are 

 very acute and may be made up of thousands of simple eyes. 

 Stridulating organs are rare among aquatic arthropods, but the 

 songs of land types are well known. Organs of hearing are pro- 



