REPORT ON THE PTEROPODA. 
71 
2. The cerebro-brachial connective may be either (i.) adventitious or (ii.) primitive. 
(i.) It is impossible to deny the tendency of neighbouring ganglia, when they 
are homonymous or successive, to become united by nervous threads. On 
considering, for example, a large number of Streptoneura, it will be seen 
that the left anterior visceral ganglion (subintestinal, left pallial, or parietal 
ganglion) is united by a connective to the right pleural ganglion, with which 
it has really nothing to do (e.g., Cassidaria )} 
In Natica the propedal ganglion is not united to the cerebral ganglion ; 
in the female Nautilus the ganglion which innervates the internal labial 
tentacles 1 2 (which does not represent, it is true, the whole brachial ganglion of 
a Dibranchiate, but nevertheless corresponds to a part of it) has also no 
cerebral connective. It might possibly be said, then, that the cerebro- 
brachial connective of the Dibranchia is only an adventitious arrange- 
ment. 
(ii.) This connective may, however, be a primitive structure, and represent an 
anterior part of the original cerebro-pedal connective, which the brachial 
ganglion has carried along with it on its separation from the pedal gan- 
glion. 
Grobben 3 4 regards this connective as a detached part of the primitive 
cerebro-pedal connective, and I share his opinion ; but I may remark that 
there is a contradiction in Grobben’s view, according to which the brachial 
ganglion should be a detached part of the cerebral ganglion, since then two 
parts of the cerebral ganglion would be joined by a cerebro-pedal connective. 
If, however, I regard the union of the brachial and cerebral ganglia of a 
Dibranchiate as primitive in the same way as the union of the brachial 
and pedal ganglia, I must remember that the first union is brought about 
by a simple connective and the second by the central ganglionic substance, 
w T hich is a very different matter. 
VI. Great importance has been attributed to the supracesophageal commissure which 
connects the two brachial ganglia in Eledone ,* and it has been regarded as a clear proof 
that the brachial ganglia were primitively supracesophageal. 5 
This commissure has only been recorded by Dietl, and only in Eledone. I have seen 
it neither in Sepia, Loligo, nor other Decapods ; and I may further remark that the infra- 
cesophageal commissure between the brachial ganglia existing in all Cephalopods is much 
1 Spengel, Die Geruchsorgane und das Nervensystem der Mollusken, Zeitschr. f. wiss. Zool., Bd. xxxv. pi. xvii. 
fig. 4, s'. 2 Owen, Memoir on the Pearly Nautilus, pi. vii. fig. 1, 8. 
3 Zur Kenntniss der Morphologie und der Verwandtschaftsverhaltnisse der Ceplialopoden. Art. Zool. Inst. Wien, 
Bd. vii. p. 69. 
4 Dietl, Untersuchungen fiber die Organisation des Gehirns wirbelloser Thiere, Sitzungsb. d. lc. Akad. Wiss. Wien, 
Bd. lxxvi. pi. v. fig. 23, dr. 5 Grobben, loc. cit., p. 69. 
