CEREBRAL HOMOLOGIES. 



39 



answers to the epencepbalon of the fish ; it is not a " sub- 

 oesophageal ganghon," but a " supra-" or " neuroesophageal " 

 one, and the foremost of that series of the neural centres or 

 gangUons." 



The homologue of the vertebrate myelon in Invertebrates 

 is not protected by a special bony case or vertebral column." 

 The " ganglionic cord " is nevertheless the most precious, as 

 it is the most deUcate and crushable of an insect's organs. 

 Hence it has been, so to speak, ordained that the part of the 

 body's surface to which the neural axis is nearest should not 

 be, as in the beast, along the part most exposed and hable to 

 blow^s. By a modified flexure of the limb-segments the trunk 

 of a beetle or lobster is turned so as to hold the same relative 

 position to the ground as does the part of the beast's body 

 least exposed to injuries. 



The aspects of the trunk in locomotion are no primary 

 or essential characters of a natural group. Some insects, 

 indeed, swim with their neural surface upwards, as does the 

 fish. 



Active Bimana, in the aspects of the trunk, differ from both 

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

 angles to the ground, and the Hmbs 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 supraoesophageal 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 anato- 

 mist admitted an exception in favour of the highest Cepha- 

 lopoda*. 



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



