GRADATIONS IN THE BRAINS OF INSECTS 243 



Within the limits of the same order the stalked bodies are most 

 perfect in the most intelligent forms. Thus in the Orthoptera, says 

 Viallanes, the Blattse, Forficulae, and the crickets, the mushroom 

 bodies are more perfect than in the locusts, which have simpler 

 herbivorous habits. This perfection of the mushroom bodies is seen 

 not only in the increase in size, but also in the complication of its 

 structures. Thus in the groups with lower instincts (Tabanus, 

 ^Eschna) the stalk does not end in a calyx projecting from the 

 surface of the brain, but its end, simply truncated, is indicated 

 externally only by an accumulation of the ganglionic nuclei which 

 cover it. 1 



In types which Viallanes regards as more advanced, i.e. (Edipoda 

 and Melanoplus, the end of the stalk projects and is folded into a 

 calyx. 



The brain of the cockroach (Periplaneta, Fig. 258) is a step higher 

 than that of the locusts, each calyx being divided into two adjacent 

 calices, although the cockroaches are an older and more generalized 

 type than locusts. 



The stalked bodies of cockroaches are thus complex, like those 

 of the higher Hymenoptera, the calices in Xylocopa, Bombus, and 

 Apis being double and so large as to cover almost the entire surface 

 of the brain. 



Finally, in what Viallanes regards as the most perfect type (Vespa), 

 the sides of the calices are folded and become sinuous, so as to increase 

 the surface, thus assuming an appearance which, he claims, strongly 

 recalls that of the convolutions of the brain of the mammals. 



Cheshire also calls attention to a progression in the size of these appendages, 

 as well as in mental powers as we rise from the cockchafer (Melolontha vul- 

 garis) to the cricket, up to the ichneumon, then to the carpenter bee, and finally 

 to the social hive bee, "where the peclunculated bodies form the i part of the 

 volume of the cerebral mass, and the ^ of the volume of the entire creature, 

 while in the cockchafer they are less than the ^Vff P art - The size of tne Drain 

 is also a gauge of intelligence. In the worker bee the brain is T t T of the body ; 

 in the red ant, ^ > in the Melolontha, ^<j<y > in the Dyticus beetle, ^5-" 

 (Bees and bee-keeping, p. 54.) 



g. Functions of the nerve-centres and nerves 



As we have seen, the central seat of the functions of the nervous 

 system is not the brain alone (supraoesophageal ganglion), but each 

 ganglion is more or less the seat of vital movements, those of the 



1 Viallanes' assertion that the instincts of the horse-flies and dragon-flies are 

 " lower" than those of the locusts, may, it seems to us, well be questioned. 



