

of Ommastrephes todarus. 7 



would appear to be the source of the motor power of the parts 

 it supplies, while the median, being in connexion with the or- 

 gans of sense, is probably more particularly the seat of sen- 

 sation, and the nerves therefore it gives to the arms, sensitive. 

 This interesting part of the subject requires further investiga- 

 tion ; but from what has just been seated, it would seem that the 

 ventral connexion of the two suboesophageal masses can scarcely 

 be looked upon in the ordinary light of a commissure ; and thus 

 it would appear that the second union, — that passing above the 

 oesophagus, and coming apparently from the apex of the optic 

 ganglions, is the true commissure between the anterior and me- 

 dian suboesophageal masses. 



The third or posterior suboesophageal nervous centre is broad 

 and trilobed, and is attached to the posterior margin of the me- 

 dian centre, and is consequently situated close under the oeso- 

 phagus. The exact mode of attachment could not be determined 

 with sufficient accuracy ; but it seems to be effected by a fusion 

 of the lateral parts with the commissure uniting the optic to the 

 median suboesophageal mass ; and as the great collar around the 

 oesophagus seems to be formed of three portions, there can be 

 little doubt that the lateral parts of this ganglionic mass are also 

 united above that tube. 



This mass is represented in Octopus by a large flat ganglion, 

 forming as it were the posterior portion of the mass giving off 

 the brachial nerves ; and in Nautilus by what has been desig- 

 nated the posterior suboesophageal ganglions. 



In Ommastrephes the mass is indistinctly formed of three 

 ganglions, the homologues of the visceral and branchial of 

 the Gasteropods; the visceral (PI. I. figs. 1, 2, 3 e) appears to 

 be single, and is placed between the two branchial {/,/). 

 These ganglions vary very much in form and situation in the 

 lower mollusks, being sometimes above and sometimes below 

 the oesophagus ; but the visceral are always connected to the 

 branchial, and the latter to the cerebroids and pedial, and it 

 frequently happens that there is apparently only one visceral 

 ganglion, which is placed between the branchial exactly as in 

 Ommastrephes. A similar arrangement occurs in Onchidium and 

 Vaginulus, and in these mollusks they are situated below the 

 oesophagus. The branchial ganglions of the Gasteropods have 

 been so named, because they are deemed homologous with those 

 of the same name in the Lamellibranchiata ; and because in Doris 



ey send a filament to the branchio-cardiac ganglions of the 



mpathetic system; and moreover they furnish nerves to the 

 mantle, which, perhaps, in all the Mollusca is accessory to the 



ecial breathing organs. 



