320 Comparative Animal Physiology 



The interaction between the brain and subesophageal gangHa is clearly 

 shown by the work of Roeder on the praying mantis.^'^^ When one side of 

 the protocerebrum is removed the legs lose tone on the opposite side; the 

 legs on the operated side are more active, and the leg sequence changes. 

 Circusing is to the normal side. When both protocerebral lobes are destroyed, 

 leg tonus is lost on both sides, and there is locomotor resdessness. The mantis 

 walks straight ahead, fails to avoid objects, and shows no head motility or 

 backward walking. When the protocerebrum is split there is decreased leg 

 movement, high neck and prothoracic tonus, and active visual responses (fol- 

 lowing of moving objects). When the subesophageal ganglion is removed 

 there is no locomotion except in response to strong stimulation. Roeder con- 

 cludes that the subesophageal ganglion excites locomotor activity in thoracic 

 ganglia, that the protocerebral ganglion has inhibitory centers controlling 

 the irritability of the subesophageal locomotor center and excitatory centers 

 maintaining tonus and activity in neck and prothoracic muscles; these pro- 

 tocerebral centers are homolateral, are inhibited contralaterally by each other, 

 and are strengthened by homolateral sensory impulses. Sometimes in mating, 

 after clasping, the female eats the male, head first, and copulation continues 

 actively. If only the brain is removed there is no sexual activity, but if the 

 subesophageal ganglion also is removed the male makes copulatory move- 

 ments and the female will receive the male.^^"* The copulatory center is in 

 the last abdominal ganglion and this is normally inhibited by the subesoph- 

 ageal ganglion. Thus the eating of the head, including the subesophageal 

 ganglion, by the female actually releases copulatory activity! 



Some arthropods exhibit very complex behavior, some of which may re- 

 quire the presence of the brain. A brainless hermit crab will not reenter its 

 shell unless it is helped by having the telson pushed in;^*'^ the hermit crab 

 without brain will grasp a new shell but fails to investigate it as a possible 

 dwelling-place. In some arthropods (female Bomhyx and Carcinus), mating 

 occurs in brainless individuals, whereas in others (various butterflies) it 

 does not. 



There is ample evidence that some insects have capacity for learning. Ex- 

 periments concerning the possible relation of parts of the brain to learning 

 should be very profitable. The functions of the specific lobes of the brain 

 can be partly inferred from their connections as shown in Table 78. Re- 

 moval of the globuli (the cellular portion of the corpora pedunculata) in 

 Carcinus causes the loss of certain responses to light, and of sidewise locomo- 

 tion; the globuli are inhibitory centers of the brain. ^^ In the myriapod Lith- 

 ohius-^'^ the protocerebrum inhibits the ventral motor centers and controls 

 the sense of direction; the protocerebrum is an inhibitory center in the man- 



In summary, then, the brains of arthropods not only are connected with 

 the most important sense organs of the body, but they also exert important 

 integrative, particularly inhibitory, control of the ventral motor centers. It 

 should be profitable to investigate localization of function within the arth- 

 ropod brain and the mechanisms of interaction between the brain and ven- 

 tral ganglia, and between the subesophageal and other ventral ganglia. 



Cephalopods. Cephalic dominance has developed in a somewhat different 

 manner in cephalopod molluscs. The brain and some thoracic ganglia of 



