500 
PAUL PELSENEER. 
has remained quite intact this secretion had spread outwardly, 
had become coagulated under the influence of the spirit, and 
had formed a stratified deposit, which absorbs much colouring 
matter on the surface of the cone. 
Each group of epithelial cells is provided at its centre with a 
sensorial cell with a rod-like prolongation. This fact deter- 
mines the buccal cones of Clione as organs of special sensi- 
bility. A refracting body is invariably found towards the 
central part of the epithelial groups at the base of the cells ; 
it is also probably, on account of its situation in contact with 
the rod, an integral part of the sensorial apparatus. 
With respect to the special nature of these organs, I may 
make a remark with reference to the sense of smell in aquatic 
animals. Is smelling possible in water, such as exists among 
the superior Yertebrata? I do not think so. There must be 
a special sense of which Mammalia cannot be conscious ; and a 
truly aquatic animal cannot have an idea of the smelling of 
aerial animals. This sense must be a peculiar one, interme- 
diate to that of smell and that of taste. The buccal cones of 
Clione are probably the seat of such a sense. 
II. — Clionopsis . 1 
Clionopsis only possesses one kind of cephalic appendages — 
tentacles properly so called. 
As with Clione, there are two pairs — a labial pair and a 
nuchal pair (fig. 5). 
The labial tentacles are less elongated than with Clione. 
As in the latter they are inserted more dorsally than ven- 
trally. Their structure is that of the corresponding appendages 
of Clione. 
The nuchal pair has already been described by Troschel. 2 
Gegenbaur says that it is absent. 3 Upon the specimen which 
1 The species studied is Clionopsis Krohni, Troschel, — ' Clio, medi- 
terranea, Gegenbaur. 
2 Troschel, “ Beitrage zur Kenntniss der Pteropoden,” ‘Arch, fur Naturg.,’ 
1854, p. 229. 
3 Gegenbaur, ‘ TJntersuchungen fiber Pteropoden und Heteropoden,’ p. 70, 
Taf. iv, fig. 14. 
