38 



CONARTO-HYPOPHYSIAL TRACT. 



superadded, in both, to the centre receiving the impressions 

 of those nerves. Such homology legitimately extends from 

 Cephalopods to the Invertebrates in v^^hich a homologue of 

 the vertebrate hemispheres may not be so largely developed 

 or superadded. 



Accordnigly I conclude that the collective neural centres 

 and their intercommunicating tracts in Invertebrates are the 

 homologues of those centres and tracts called " brain and 

 spinal cord " in Vertebrates, and that such " neural axis " 

 marks, in both grades of the animal series, the same position 

 in the body, and the same local relations to the vascular 

 centre, m, and the ahmentary canal (fig. 11, /). As a corol- 

 lary, the neural axis, or " ganglionic cord " in Arthropods 

 {h 0 71) denotes the neural position, and supports the inference 

 that its foremost portion, is simply displaced by the course 

 of the gullet through the brain in order to open by a mouth 

 upon the neural aspect of the body (as in fig. 3). The sup- 

 pression of such transcerebral tract in Vertebrates allows the 

 continuation of the alimentary canal forwards to an oral 

 opening on the hsemal aspect of the body (as in fig. 2). 

 Here the oesophagus offers no obstacle to the approximation 

 of the main cerebral centres to each other — the fore brain to 

 the hind brain. Hence that juxtaposed allocation of the 

 primary encephalic divisions, associated with the progressive 

 accumulations of grey and white neurine, which the cerebrum 

 and cerebellum present, in relation to the centres subservient 

 to the ingoing conductors of sensations and the outgoing 

 ones of motions, as we pass in their contemplation from the 

 fish to the ape and the man. 



The so-called " brain " in the Locusts answers to a part only 

 of the brain of a fish; moreover it is not a " supraoesophageal 

 ganglion," but a "sub-" or " haemoesophageal " one 



The next neural mass in the brain of the Locust [h] 



