REPOET ON THE PTEROPODA. 
67 
contrary, the dorsal half of the mass of the arms is sometimes more voluminous than the 
ventral mass (compare, for example, Nautilus ), but, nevertheless, the nervous centre 
which innervates the whole brachial mass is situated exclusively on the loiver surface of 
the oesophagus. This shows clearly that the brachial mass does not originate from the 
dorsal, but in the ventral parts of the animal (that is from the foot), and that its two 
halves have been fused above the head ; this view is confirmed, as we shall see in the 
sequel, by the embryology of these organs. 
II. Grobben 1 states that the arms of the Cephalopoda were primitively lateral to the 
mouth, as are the cones of Clione. In the latter, however, all the cones, both ventral 
and dorsal, are innervated by the supracesophageal ganglia. If, then, the arms of the 
Cephalopoda and the cones of Clione were morphologically homologous, it would be 
impossible to understand why, the disposition of these organs being similar, the disposition 
of their innervating organs should be different. But I have shown that the cones of 
Clione and the buccal appendages of the other Gymnosomata are organs formed on the 
inner wall of the evaginable proboscis, which is made up of the anterior portion of the 
digestive tract, and whose cephalic nature is therefore indisputable. The relation of the 
arms of the Cephalopoda to the anterior part of the digestive tract is entirely different. 
Supposing, however, that the arms are really cephalic appendages, primitively situated 
at the sides of the buccal opening, w T e might compare them with the absolutely identical 
arrangement which we see in Ampullaria. Here we find on either side of the mouth 
(not more dorsally than ventrally) a large conical appendage, elongated, voluminous, and 
relatively as large as several arms of a Cephalopod. 
How then are these appendages innervated ? By the supraoesophageal or cerebral 
ganglia . 2 These appendages probably correspond with the labial palps of certain Pul- 
monata {Helix, Glandina, &c.), whilst the appendage situated in front of the eye 
corresponds with the nuchal tentacle or rhinophore of the Eutliyneura, inasmuch as it 
encloses the highly ramified olfactory nerve . 3 
III. In Vermetus, on the other hand, we find between the mouth and the foot two 
long appendages (buccal tentacles of d’Orbigny ; tentacular or antibuccal filaments of 
Quoy and Gaimard), which stand precisely in the same position as the ventral arms of the 
Cephalopoda, and as far separated from the pedal disc as these arms are from the funnel, 
upon the pedal origin of which no doubt has ever been thrown. 
How then are these appendages innervated? By the anterior suboesophageal or pedal 
ganglia, as has been shown by Lacaze Duthiers , 4 and as I have been able to convince 
myself in the case of Vermetus gigas. 
1 Zur Kenntniss der Morphologie, &c., lor,, cit, pp. 68, 70. 
2 Anatomie von Ampullaria urceus, Archiv f. Naturgesch., Jahrg. xi. p. 200, pi. viii. fig. 3, b. 
3 Ibid., pi. viii. fig. 3, e'. 
4 Memoirs snr l’anatomie et l’embryogenie des Yermets, Ann. d. Sci. Nat., Zoologie, s4r. 4, t. xiii. p. 238, pi. vi. 
fig. 4, s'. 
