Sauropsida: Class Keptilia 181 



operation of inherited specialized nervous mechanisms. They are 

 instinctive activities. The young animal does not have to be taught. 

 As its nervous mechanisms acquire complete development, the animal 

 automatically and inevitably carries out the activities which are normal 

 and characteristic of its species. And yet this instinctive determination 

 of behavior is not complete and rigid. Even an earthworm can be 

 "taught" to modify its behavior and may "learn by experience "- 

 which does not necessarily imply intelligence. So also, in fishes and 

 amphibians, there is a certain degree of flexibility in the pattern of 

 behavior. To a very limited extent a fish may learn by experience and 

 may modify its customary behavior. In amphibians, and especially 

 in frogs and toads, the capacity for modifying behavior is somewhat 

 greater than that in most fishes (so far as can be judged from the scanty 

 data available). In fact, some observers have gone so far as to ascribe 

 intelligence to frogs and toads. If, however, intelligence is to be under- 

 stood as implying deliberate thinking about two alternative lines of 

 action and contrasting the desirability of their foreseen consequences, 

 then it is quite certain that the evidence at hand does not warrant 

 describing these animals as intelligent. 



The behavior of reptiles is certainly on a higher level than that of 

 amphibians in general, but perhaps not so much higher than that of 

 toads. The common toad seems to have achieved the peak of behavior 

 for amphibians. Reptiles can learn, remember, and form new habits. 

 They respond more quickly than amphibians. Here, again, there is no 

 proof of intelligence, but an interested observer of reptiles is likely to 

 find it difficult to restrain himself from crediting them with faint 

 glimmerings of something akin to intelligence at its lowest level. 



Fishes, amphibians, and reptiles constitute a series in which the 

 degree of differentiation of the muscular system, the diversity and 

 complexity of the animal's activities, and the adaptive modifiability 

 of behavior are at the minimum in fishes and at the maximum in 

 reptiles. Parallel to these differences, the cerebral hemispheres in the 

 series are successively more strongly developed. The pallium, non- 

 nervous in most fishes, becomes an important nervous layer in amphib- 

 ians and, in reptiles, possesses a "gray" cortex resembling that of a 

 mammal. Therefore the fact that the cortex of the mammal contains 

 the nerve-centers responsible for such intelligence as the animals' 

 behavior may exhibit has some implications for reptiles. 



From the reptilian brain arise 12 pairs of cranial nerves. Of 

 these, 10 pairs correspond in all particulars to the 10 pairs al\\a>s 

 present in fishes and amphibians. The eleventh (accessory) and 

 twelfth (hypoglossal) arise from the extreme hind end of the brain 

 and behind the tenth pair. The embryonic origin and the connections 



