836 Comparative Animal Physiology 



brain from elasmobranchs and teleosts causes no disturbance of posture and 

 locomotion. Also the fish forebrain has integrative functions, as indicated 

 bv operative studies on goldfish (^Carassius'-^'^) and on Phoximis and Gohio. 

 -^^ Fish without forebrains show nearly normal "spontaneous" activity and 

 change in position without specific environmental stimulation, but lose "in- 

 itiative"— the ability to react to stimuli in a specific, non-reflex manner. Speed 

 of locating and seizing food is unaffected; the variability in frequency of 

 spontaneous movements of opercula and eyes is diminished, and the oper- 

 ated fish after being on a given background tend to select a background of 

 the same brightness rather than a dark background, as preferred by normal 

 fish. Fleeing is elicited by general exciting stimulation in both normal and 

 operated fish; but the fish without forebrains fail to aggregate as much as 

 normal fish, particularly when individuals are separated by wide-mesh screen- 

 ing. Holocentnis lacking all of the forebrain can still learn to feed from the 

 experimenter's hand.-^'"* 



The forebrain of a frog shows much spontaneous electrical activity even 

 when it is isolated.^*'" Electrical stimulation of the forebrain, as in fishes, 

 elicits no motor response.'-*^' Lessening of both spontaneity and initiative as 

 a result of removal of the forebrain from frogs and salamanders is both af 

 firmed^ ^^ and denied;^^^ active feeding diminishes, although chewing and 

 swallowing are normal. Comparable reduction in foraging does not result 

 when eyes and nasal organs are removed from amphibian embryos without 

 brain interference."^ Some conditioned responses are lost after forebrain re- 

 moval."^ The swimming of a male frog toward a female at the time of 

 spawning is a midbrain response which is facilitated by the forebrain.^** Thus 

 the amphibian forebrain appears to be more important in integration than is 

 the fish forebrain. 



Little is known of forebrain function in reptiles, although an electrically 

 excitable area has been described for turtles and lizards^-^ and for alligators,^" 

 but its presence was not confirmed in alligators and Iguaria (Straus, per- 

 sonal communication), or in the lizard Lacerfa.^"' However, in Lacerta the 

 motor responses elicited by stimulation of the tectum were modified by simul- 

 taneous stimulation of the cortex. Straus reports no visible response in four 

 alligators on stimulation of the cerebral cortex (with a unipolar electrode). 

 All reactions secured could be interpreted as the result of spread of current 

 or as "pain" reactions. In three iguanas similar stimulation produced incon- 

 stant and variable contractions of muscles of the head, neck, and trunk, but 

 none at all of the muscles of the extremities or tail. It seems doubtful wheth- 

 er the results secured in Iguana can be regarded as constituting proof of the 

 existence of a true "motor" cortex. 



There appear to be no recent studies on electrical stimulation of the non- 

 laminated cortex in birds, and older experimenters disagree regarding the ex- 

 istence of excitable areas. It appears certain, however, that removal of the 

 hemispheres from pigeons makes the birds listless and uninterested in their 

 environment; the operation interferes somewhat with reproductive behavior, 

 although the birds can maintain their equilibrium and can erect their feath- 

 ers and maintain body temperature.^*'^ With cortex gone but the entire 

 striatum intact, some birds mated and reared young.^^^ The operated birds 

 learned to eat after some weeks. Forebrainless pigeons were able to avoid 



