IN VERTEBEATES AKD INVERTEBRATES. 7 



The aspects of the trunk iu locomotion are no primary or essen- 

 tial characters of a natural group. Some insects, indeed, swim 

 with their neural surface upwards, as does the fish. 



Active Bimana, in the as[)ects of the trunk, differ from both 

 beasts and beetles : when a man stands, his body is at right angles 

 to tbe ground, and the limbs are in the same line with the 

 trunk. But the heart in man indicates the " haemal!" aspect, the 

 myelon the " neural " aspect, as in the animals of lower grade, 

 whether vertebrate or invertebrate. 



The restriction by Cuvier of cerebral homologies to the so-called 

 " supracesophageal ganglion " in the latter zoological division 

 leads me to add a few remarks on what may be derived from the 

 molluscous subkingdom in illustration of my present subject. In 

 this group, indeed, the great anatomist admitted an exception in 

 favour of the highest Cepbalopoda *. 



In fact, the encephalon in the Dibranchiate order resembles 

 that of Vertebrates in the mutual proximity of the " fore " and 

 " hind brains ; " so approximated, they are both also protected 

 partially by a cartilaginous case which, with some histological 

 modification, is analogous to, if not homologous with, the verte- 

 brate cranium. 



But the cephalopodic brain retains the invertebrate condition 

 of giving passage to the gullet along the tract or part answering 

 to the third ventricle ; only the lateral boundaries or crural tracts 

 are much shorter and thicker than in inferior Mollusks or in 

 Articulates. 



Still it is plain that tbe nervous mass on one side of the gullet 

 answers to the " supracesophageal ganglion," and that on the 

 opposite side to the " suboesophageal ganglion" of lower Inver- 

 tebrates. 



The latter, in Cephalopods, sends off the acoustic nerves, and is 

 continued into the cords which endow the muscles and skin of the 

 trunk with the motory and sensory powers. A closer resemblance 

 than is usually seen iu Invertebrates to the Vertebrate myelon is 

 moreover manifested by the conspicuous ganglions developed on 

 the sensory tracts or cords of the trunkf, and the non-ganglionic 

 continuation of the motory division of the body-cords continued 

 from the Cepbalopod's brain. 



* Op. cit. torn. iii. p. 297. 



t ' Anatomy of the Pearly Nautilus,' 4to, 1832, p. 38, pi. 7. fig. 3. 



