14 
THE VOYAGE OF H.M.S. CHALLENGED. 
But, in addition to the five large plates, several species have in front of them double 
the number of small plates (PL II. fig. 5, b) ; these latter 1 are triangular, and are situated 
in front of the four large symmetrical plates and of the intervals between them. They 
alternate in size, the four which are situated in front of the large plates being smaller 
than the others. 
In most species of Clio a narrow caecum of varying length opens into the posterior 
portion of the stomach. 
The liver agrees in form and situation with that of Limacina, but its duct opens into 
the posterior part of the stomach on the right side (PI. II. fig. 1). Clio ( Creseis ) acicula 
retains in this respect a primitive disposition, the part corresponding to the liver in the 
adults of other species being but slightly developed. 
The intestine is bent to the left and ventrally ; 1 2 its termination is at a greater or less 
distance forward, according to the subgenus in question ; in Creseis and Hyalocylix (PL 
II. fig. 1) the anus is placed very far back in consequence of the great length of the 
oesophagus ; in Styliola the oesophagus is not so long, and the intestine terminates further 
forwards ; lastly, in Clio (s. str. ) the anus is situated far forwards, not far from the 
aperture of the mantle (Pl. II. fig. 7, e). 
In the pallial cavity, close to the anus, between the mantle and the intestine, is a 
flattened gland, somewhat triangular in form and somewhat similar in structure to the 
shield (pallial gland). This organ (Pl. II. fig. 7,/), which I propose to call the “anal 
gland,” does not appear to have been mentioned by any previous author. 
The Circulatory and Excretory Organs. — The disposition of the central circulatory 
organ is well known (Pl. II. fig. 8) ; it is situated on the ventral surface in front of the 
genital gland ; the auricle (b) is behind and the ventricle (a) in front. Both are rather 
elongated, and situated in a very long pericardium (c). 
The kidney is jflaced close to the latter (Pl. II. fig. 8, d) ; it is flattened, with thin 
almost transparent walls, and has the form of an elongated more or less recurved triangle, 
the apex being directed backwards. It communicates (through f) with the pericardium 
and opens into the pallial cavity by a narrow orifice (e), situated towards the left 
angle at the base of the triangle. This orifice escaped the notice of Souleyet, 3 so that he 
was unable to interpret the kidney correctly. 
As to the gills, they are entirely absent in Clio as well as in Limacina. The organs 
which have been regarded by previous writers (van Beneden, 4 Souleyet, 5 &c.) as gills are 
merely folds of the mantle in specimens preserved in spirit. 
1 They are visible even in the larvse ; compare Fol, Sur le developpement des Pteropodes, Arch. d. Zool. Expe'r ., 
ser. 1, t. iv. pl. vi. fig. 8, sp. 
2 Gegenbaur is mistaken when he depicts (Untersuchnngen fiber Pteropoden und Heteropoden, pl. ii. fig. ], g) the 
intestine as curved dorsally in Clio ( Creseis ) acicula. 
3 Voyage de la Bonite, Zoologie, t. ii. pp. 168, 169. 4 Exercices zootomiques, part ii. p. 42. 
6 Voyage de la Bonite, Zoologie, t. ii. p. 170. 
