6 Mr. A. Hancock on the Nervous System 



of two filaments which soon diverge, and passing forwards above 

 the oesophagus go to be united to the posterior margin of the 

 upper pair of buccal ganglions. 



This connexion of the optic with the buccal ganglions has not 

 been observed in the Gasteropods ; but it is possible enough that 

 such connexion may exist, for the commissure which unites the 

 buccal to the cerebroid in these animals leaves the latter not far 

 from the attachment of the optic ganglions. Yet it must be ex- 

 pected that in the lower mollusks some deficiencies with regard 

 to the optic apparatus exist, when the low state of their visual 

 power is_ compared with its perfection in the Cephalopods. 



There is another apparent anomaly in respect to the optic 

 ganglions of Ommastrephes. Other two cords or commissures 

 would seem to be given off from the apex of these centres. 

 These cords (PI. I. figs. 1, 2, ^ d, d, %l PI. II. figs. 1, 2 c) issue 

 from the sides of the apex and from the under surface ; but on 

 close examination have all the appearance of being connected to 

 the median sub oesophageal centre through the commissure which 

 unites the latter to the optic ganglions. This, however, was not 

 perfectly demonstrated, though there can be little doubt of the 

 fact. These cords course forwards above the oesophagus, having 

 the optic commissure, just described, between them, and are joined 

 to the upper and posterior margin of the anterior suboesophageal 

 mass close to and behind the roots of the cords which unite this 

 centre to the buccal ganglions. Now it has already been shown 

 that there exists a peculiar connexion between the anterior and 

 median masses below the oesophagus; it is therefore a matter of 

 some interest to ascertain what is the nature of this second union. 

 That first described was effected, it will be recollected, by a cord 

 composed of numerous stout filaments, most of which, though 

 attached to the under surface of the anterior ganglion, did not 

 appear to enter it, and that becoming joined to the brachial nerves 

 from this centre entered the arms in union with them. Thus the 

 nerves that supply these organs are derived from two sources,- — 

 have in fact two roots, arising much in the same manner as the 

 sensitive and motor roots of the spinal nerves of the Vertehrata. 

 I have observed something of the same sort in the Gasteropods ; 

 in Thetis, the nerves supplying the veil appear, on passing from 

 the cerebroid ganglions, to have two roots. 



The sensitive and motor influences in the Mollusca must be 

 assumed to reside in all the ganglions. And here it may be 

 asked, dowe not see, in the peculiar mannerwith which the brachial 

 nerves are supplied in this Cephalopod, something almost ap- 

 pi-oaching to a proof of the fact that these powers have even in 

 the Invertebrata their own peculiar centres ? The anterior mass 



