THE M-'.R I 'O US S YSTEM. 



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. 



Flogel, 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 i ]'cspa), 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 Flogel 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. 



Yiallanes, 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 Yiallanes confesses that he 

 adopts a ' monographic style, so that the interest of special 

 facts may not be masked by ha/ard<>us 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 



