22 
THE VOYAGE OF H.M.S. CHALLENGER. 
situated in front of the lobe which bears the operculum. 1 (It has already been remarked 
that the larval Cymbulise have an operculum. 2 ) 
So far as I can judge, this appendage seems to be most properly comparable with the 
middle part of the foot of the Heteropoda which carries the sucker, and is called by 
Grobben 3 “rudimentar Sohle des Protopodiums.” These two portions occupy strictly 
corresponding situations. 
I do not, however, agree with Fol 4 that this appendage of the Cymbuliidse corresponds 
with the posterior lobe of the foot of the Gymnosomata. I think rather that this last 
is homologous with the central and posterior parts of the foot of the Aplysioidea. 
The Mantle extends ventrally, and also a little dorsally, much further than in the 
Cavoliniidse, in order to form the cartilaginous “ shell,” which is in fact nothing more nor 
less than an induration of the subepithelial dermic layer of the mantle. 
The pallial gland (PI. III. fig. 8, a ; PL IY. fig. 7), which is a modification of the 
internal epithelial layer of the mantle, differs from that of the Cavoliniidse in being 
obviously asymmetrical, the right portion being the larger. It is divided into anterior 
and posterior parts by a transparent band, which is itself asymmetrical (see PI. III. 
fig. 8). 
Since Cymbulia does not possess a true shell, the columellar muscle, corresponding 
to that of the Limacinidse and Cavoliniidse is entirely wanting. 
The space between the fin and the “shell” (PI. IY. fig. 1 , d) is freely open and leads 
into the pallial cavity. On removing or cutting through the fin (PI. III. fig. 7, e) the 
opening of the mantle-cavity is seen to be asymmetrical, thus differing from that of the 
Cavoliniidse ; this opening is in fact decidedly turned to the right. 
In consequence of the reduction of the dorsal surface of the animal the pallial cavity 
appears to extend along the dorsal side to just below the heart (PL IY. fig. 1, n) between 
the kidney and the visceral mass ( h ) (digestive and generative organs), 5 which 
appears to hang freely into the mantle-cavity. It must be noticed that the aboral 
extremity of this visceral mass almost corresponds to the ventral prominence of the same 
mass in Cavolinia gibbosa, for example, where there is a tendency to the dorso- ventral 
elongation so pronounced in Cymbulia. 
Thus the ventral surface of Cymbulia reaches a little further than this aboral ex- 
tremity of the viscera] mass. 
On either side of the visceral mass there may be seen on the inner wall of the mantle 
rather large muscular bundles, arising where the fin joins with the visceral mass and 
1 Krohn, Beitrage zur Entwickelungsgeschichte der Pteropoden und Heteropoden, pi. i. fig. 13, d. 
2 Zool. Chall. Exp., part lxv. pi. ii. fig. 14. 
3 Zur Morphologie des Fusses der Heteropoden, Arb. Zool. Inst. Wien, t. vii. p. 224. 
4 Sur le d4veloppement des Pt4ropodes, Arch. d. Zool. Expdr., s4r. 1, t. iv. p. 193. 
6 This is clearly shown in fig. 1 of my systematic Report on the Thecosomata (ZooL Chall. Exp., part lxv. 
p. 97). 
