HOMOLOGY. 



25 



off the nerves to the prehensile arms, and are in communica- 

 tion with the viscera, the muscles, and the soft parts of the 

 trunk. Moreover, in Vertebrates this epencephalic homologue 

 is in direct nervous communication v^ith the organ of hearing 

 (fig. 9, h\ and fig. 10, h). The fore brain, on the opposite 

 side of the gullet in the Cephalopod (fig. 9, a)^ supplies the 

 nervous masses subservient to the large and complex organs 

 of vision, and also parts which may exercise the sense 

 of smell. But, if the subuosophageal mass and the moto- 

 sensory neural continuations of the trunk, t, be, in the Ce- 

 phalopod, homologous with those in the Insect (fig. 3, i) and 

 Crustacean, the ground on which I predicate, in the Arti- 

 culate, of the neural aspect of the body, that it answers to 

 that commonly called " dorsal " in Vertebrates, is applicable 

 also to the MoUusk, fig. 9. 



Therefore the part which Cuvier indicates in his diagram, 

 and terms brain ('' cerveau," a), is not a true criterion of the 

 back (" dos ") ; it occupies in the Cephalopod and other 

 cerebral Invertebrates the aspect of the belly, or tract of the 

 body which I term " haemal," and which is called the ventral 

 or under part. 



To be sure this cannot be predicated of the brain (" cer- 

 veau," a) of the quadruped. And why? Because the ah- 

 raentary tract and outward anterior opening which would 

 demonstrate its holding a position opposite to that of the rest 

 of the nerve-centres has been atrophied, and exists as an 

 arrested residuary embryonal part (figs. 3 and 10, 7-8). It 

 is the superadded respiratory organization in connexion with 

 the oral end of the ahmentary canal and the concomitant 

 opening of the mouth in a new position, in the Vertebrate, 

 which turns the cerebrum to the side occupied by the rest 

 of the nerve-centres — in other words, to the neural aspect of 

 the body. Individual development being achieved, the Ver- 



