62 



THE ORIGIN OF VERTEBRATES 



The supra-infundibular portion of the brain in vertebrates 

 corresponds clearly to the supra-cesophageal portion of the inverte- 

 brate brain in so far that in both cases here is the seat of the will. 

 Voluntary action is as impossible to the arthropod deprived of its 

 supra-cesophageal ganglia as to the vertebrate deprived of its cere- 

 brum. It corresponds, also, in that from it arise the nerves of sight 

 and smell and no other nerves ; this is also the case with the supra- 

 cesophageal ganglia, for from a portion of these ganglia arise the nerves 

 to the eyes and the nerves to the first antennte, of which the latter 

 are olfactory in function. Thus, in the accompanying figure, taken 

 from Bellonci, it is seen that the supra-cesophageal ganglia consist 



Sup. Segment Ant I 



Ant II 



Inf. Segment 



Fig. 27. — The Brain op Sphceroma serratum. (After Bellonci.) 



Ant. I. and Ant. II., nerves to 1st and 2nd antenna?, f.br.r., terminal fibre layer of 

 retina; Op. g. I., first optic ganglion; Op. g. II., second optic ganglion; O.n., 

 optic nerve-fibres forming an optic cbiasma. 



of a superior segment corresponding to the cerebrum, a middle 

 segment from which arise the nerves to the lateral eyes and to the 

 olfactory antennas, corresponding to the basal ganglia of the brain 

 and the optic lobes, and, according to Bellonci, of an inferior segment 

 from which arise the nerves to the second pair of antennae. This 

 last segment is not supra-cesophageal in position, but is situated on 

 the oesophageal commissures. It has been shown by Lankester and 

 Brauer in Limulus and the scorpion to be in reality the first ganglion 

 of the infra-cesophageal series, and not to belong to the supra- 

 cesophageal group. 



Further, in Limulus, in the scorpion-group, and in all the extinct 



