Nervous Systems 845 



hind a olass.'"- Eledone has been conditioned to give a chromatophore re- 

 sponse with colored Hght as the CS. 



In no other group of in\ertebrates is instinctive behavior so highly de- 

 veloped as in the arthropods, particularly in hymenopteran insects. The lit- 

 erature on social behavior of bees, wasps, and ants is more extensive than 

 for anv other group except primates. Experimental studies are fewer. Light 

 has been used successfully as a CS, associated with prod or shocking as 

 UnCS, in arthropods such as the water mite Limnesia;^^^ Cyclops, hermit 

 crabs (Ejipagitrns),-'^" Pagiirus and Leander (Mickhailoff in Razran''"*'"'), 

 and cockroaches by several authors (e.g., Hunter-^'O- Larvae and adults of 

 Tenehrio were trained to avoid rough or smooth surfaces and to make a cor- 

 rect turn in a T-maze.^'" A crude correlation has been suggested between 

 the relative size of the mushroom bodies (corpora pedunculata) and intelli- 

 aence of insects (Table 78), but no one seems to have tested the effect on 

 learnino and memory of the removal of these bodies. Lhmdus, an animal 

 with very large corpora pedunculata, has not been studied for "intelligence." 

 Arthropod behavior is modifiable within limits. 



Fish have been conditioned in many experiments, particularly to color, 

 form, and sound as the conditioned stimuli, and the habit has been retained 

 for several weeks.'^- Training in mazes has also been successful. Some fish 

 show social behavior, nest building, and care of the young, and some mi- 

 orate great distances. Removal of the forebrain from sticklebacks resulted in 

 no loss in behavior or in ability to learn color or form discrimination; also 

 after removal of the cerebellum these fish learned and retained their habits 

 well.'^"''* Goldfish have been trained to second-order responses, i.e., first to 

 visual stimulus with food as the UnCS and then to the olfactory stimulus of 

 amyl acetate with the visual stimulus as re ward. •^'^^ When parts of the tec- 

 tum were removed, particularly its anterior border, the second-order learn- 

 ing was upset; hence the site of conditioning was the tectum. There appears 

 to be much variation in the function of the forebrain (principally striatum) 

 among fish. Cichlid fish, for example, after loss of the entire forebrain 

 showed sex recognition, learned new territories, but failed to deposit or ferti- 

 lize eggs or to go in schools. In Lehistes, however, mating persisted; Hemi- 

 chromis, 19 months after a lesion to the striatum, failed to guard its eggs.-^"'^ 

 Both the tectum and striatum, then, function in certain species for learned 

 and complex instinctive behavior. 



Amphibians refuse distasteful food after a few trials. Both urodeles-'^'^ and 

 anurans'^" have been trained successfully in simple mazes. Conditioning to 

 visual and auditorv stimuli with food as UnCS occurs if the stimuli are no 

 more than 2 seconds apart.' ^•'' Associations are still formed with one side of 

 the forebrain removed but not with both halves lacking. 



Turdes have been trained in mazes nearly as readily as rats. Birds per- 

 form complex feeding, mating, nest-building, and rearing of young. Mi- 

 gration and homing are poorly understood, but certainly experience and good 

 memory of places are contributory. Many studies by conditioning and maze- 

 learning techniques have demonstrated the high order of learning in birds,^-^ 

 but few correlations with neural structures have been made. Discrimination 

 between a circle and triangle continues in the fowl after removal of the cor- 

 tical surface of the forebrain.^'^^ 



