ATROPHY OF PART OF BRAIN IN BLIND INSECTS 241 



its extent, and the tritocerebrum is situated quite far from the pre- 

 ceding segment of the brain. 



On the other hand, in insects which feed on fluid food (Hyme- 

 noptera, Lepidoptera, Diptera, Hemiptera), the oesophagus is slender 

 and the nervous centres which surround them are very much con- 

 densed ; the connectives are short, and the tritocerebrum is closely 

 fused, partly to a portion of the antennal lobes (deutocerebrum) 

 and partly to the mandibular ganglion. 



As regards the perfection of the senses, where, as in dragon-flies, 

 the eyes are very large, the optic ganglia are correspondingly so, 

 and in the same insects the antennae being very small, the antennal 

 lobes are almost rudimentary. The ants exhibit inverse conditions ; 

 in their brain the antennal lobes are well developed, while the optic 

 ganglia are reduced, and where, as in Typhlopone, the eyes are 

 wanting, they are completely atrophied. 



In certain cave insects where the eyes are wanting, the optic 

 ganglia are also absent. In the eyeless cave species of Anophthal- 



FIG. 25fi. Head of Anophthat- FIG. 257. Head of another Carabid, with the brain and 



mtix tt?llk<in//itii, show-ins: the brain, eyes normal : <>i>, optic ganglion ; pel, brain. 

 the optic ganglia, nerves, and eyes 

 totally atrophied. 



mus the optic ganglia and nerves are entirely atrophied, as they are 

 in Adelops, which, however, has vestiges of the facets (ommatidia). 

 Fig. 257 represents the brain of CMwnius penn sylvan icus, a Carabid 

 beetle, with its eyes and optic ganglia (op) which may be compared 

 with Anopthalmus, in which these parts are totally atrophied. 



Dujardin claimed that the degree of complication of the stalked 

 body of the Hymenoptera was in direct relation with their mental 

 powers. This has been proved by Forel, who has shown that in the 

 honey bee and ants the mushroom bodies are much more developed 

 in the workers than in the males or females and Yiallanes adds 



R 



