12 
THE VOYAGE OF H.M.S. CHALLENGER. 
I have scarcely been able to establish any noteworthy differences either in the principal 
parts of the circulatory and excretory apparatus, or in the organs of generation. As in 
Limacina, there are at the end of the hermaphrodite duct a large muciparous gland, an 
albuminiparous gland, and a receptaculum seminis (PI. I. fig. 11). 
Nervous System. — The cerebral and pedal ganglia are disposed as in the case of 
Limacina and all Thecosomata ; that is to say, the former, united by a long cerebral 
commissure, give origin to the nerves of the head and tentacles, and the latter to the 
nerves of the fins and posterior lobe of the foot. 
But that which distinguishes the central nervous system of Peraclis from that of 
Limacina is the arrangement of the visceral commissure. Instead of the two asym- 
metrical ganglia we have here three ganglia, the two lateral of which are symmetrical, 
and a little smaller than the central one (PI. I. fig. 1 2, c, d, e). 
This disposition is identical with that which I have already indicated as occurring 
in Cymbulia / and which, as will appear in the sequel, is characteristic of the whole 
family Cymbuliidse. 
In an animal so small as Peraclis it is very difficult to distinguish clearly the nerves 
issuing from the ganglia. I have seen, nevertheless, the nerve ( 1 ) proceeding from the 
right visceral ganglion, and a larger (genital) nerve [3) proceeding from the median 
ganglion, comparable with the corresponding nerves in Cymbulia. Further, I cannot 
doubt that the visceral nerves in Peraclis have a disposition identical with that found 
in all the Cymbuliidse ; that is to say, each lateral ganglion gives off a pallial nerve, of 
which I have made out that on the right, and the large median ganglion gives off 
from its right side a slender visceral nerve in addition to the large genital one. 
The buccal or stomato-gastric ganglia are similar in form and arrangement to the 
•corresponding parts in Limacina. 
Family II. Cavoliniid^. 
These are the typical Thecosomata, the forms which have been most frequently 
studied, and which are consequently the best known. Their visceral anatomy being 
tolerably well known, there are certain points over which I may pass rapidly. 
It has already been shown 2 that this family contains three genera, namely, Clio, 
Cuvierina, and Cavolinia, and furthermore, that the first of these includes divisions of 
subgeneric value, Creseis, Hyalocylix, and Styliola, which differ from each other in 
certain points of their organisation. We shall examine the three genera of this fa mil y 
in succession, and during the discussion of the genus Clio we shall have occasion to 
demonstrate some characters which distinguish its different sections. 
1 Recherches sur le systeme nerveux des Pteropodes, Arch, de Biol., t. vii. p. 117, pi. iv. fig. 12. 
2 Zool. Chall. Exp., part lxv. p. 41. 
