440 THE NERVOUS SYSTEM. 
of the nervous system of the Cockchafer shows that all the 
abdominal ganglia are united with the thoracic to form the 
thoracic centre in that insect. For some further remarks on 
the comparative morphology of the nervous system in insects 
see p. 62. 
b. General Structure of the Brain in the Arthropoda. 
Flégel, as early as 1877 [177], pointed out, in no equi- 
vocal terms, the great similarity of structure in the brains of 
the most diverse insect-types. With the single exception of the 
Wasp (Vespa), he showed that the differences which exist are 
not such as to justify the opinion that the cephalic centres are 
differently constituted in different insects. He speaks with 
astonishment of the great deviation of the wasp’s brain from 
the common type. That Flégel was mistaken in attributing 
marked exceptional characters to it is now, I think, indubitable. 
As yet, however, a uniform morphological nomenclature is 
wanting, so that the-general impression is that the brains of 
insects differ so much from each other, and from those of 
other Arthropods, that no such nomenclature is possible. 
Viallanes, in 1887 [183, Mem. 4], said: ‘ In different orders of 
insects, and often in genera of the same order, the brain 
exhibits unexpected peculiarities. Thus, without exaggeration, 
it may be said that the brain of a Coleopterous differs from that 
of a Hymenopterous insect as much as the brain of a Fish 
does from that of one of the higher Mammalia.’ And he adds: 
‘At the present time every hypothesis concerning the inter- 
relations of insects’ brains must be regarded as rash, as it is 
without a basis of support.’ And Viallanes confesses that he 
adopts a ‘monographic style, so that the interest of special 
facts may not be masked by hazardous generalisations.’ Such 
a style is very characteristic of the majority of memoirs on the 
insect brain. 
So far as mere difference in the proportionate size of the 
brain and the body weight is concerned, there is, I think, 
less variation in Arthropods than in Vertebrates; and, 
so far as structure is concerned, it appears to me that only 
