20 
THE VOYAGE OF H.M.S. CHALLENGER. 
seminalis, with a very short duct (Pl. III. fig. 4, c ). Cavolinia longirostris appears to 
form a transition between this arrangement and that observed in the other typical 
Cavolinise , for in this species the vesicula seminalis has the form of a long caecum, 
towards the extremity of which is a swelling, which is wanting in the other species of 
Cavolinia ( s . str.). 
On the other hand, there are in all Cavoliniae, at the distal extremity of the genital 
duct, the same accessory glands as in other Thecosomata ; a large muciparous gland 
and smaller albumen-gland close together. In group A, however, there is a pyriform 
receptaculum seminis at the end of a long duct, a little in front of these glands. 
The genital aperture (PI. III. fig. 4, e), the ciliated seminal groove (/), and the orifice 
of the penis, are situated as are the corresponding parts of other Cavoliniidse. The penis 
encloses a horny stylet (e.g., in Cavolinia trispinosa, PI. III. fig. 5), which Souleyet 1 did 
not notice in the genus. 
The Nervous System . — In Cavolinia, as in all other Thecosomata, the cerebral ganglia 
are situated at the sides of the oesophagus, and connected by a long supraoesophageal 
commissure. They are in reality cerebro-pleural ganglia, for each encloses a pleural 
centre within it. 
The pedal ganglia, as in Cuvierina, and probably all other Thecosomata, have a 
second small anterior commissure, which is readily visible in a series of transverse sections 
of the central nervous system. 
As in the case of Clio the visceral mass is formed of two asymmetrical halves, the 
right being the smaller of the two. All the figures, therefore, which represent this mass 
as symmetrical are incorrect. 
Thus in the typical Cavoliniee the visceral ganglia are disposed as in Clio, and the 
nerves take origin in the same manner. The two pallial nerves [1 and -4 in the figures of 
the nervous system) are very strong in this species, in correlation with the presence of the 
pallial appendages and of the extensible margins of the mantle. In Cavolinia injlexa the 
two halves of the visceral ganglionic mass are rather further separated, but still asym- 
metrical. 
In the forms included in group A ( Cavolinia trispinosa and Cavolinia quadridentata) 
the ganglionic elements of the visceral commissure are clearly separated, as in Cuvierina, 
into two asymmetrical ganglionic masses (the right being the smaller), but to a less extent 
than in Cuvierina. The nerves take origin in a manner similar to that described in the 
latter genus. 
This clear separation of the ganglia in group A shows beyond doubt that these species 
are the most archaic of the living forms of this genus — a view which is supported by the 
presence of the balancer, as in Clio, and the less specialised character of the foot. 
On the other hand, the absence of a gill, the characters of the mantle, of the genital 
1 Voyage de la Bonite, Zoologie, t. ii. p. 125. 
