THE GASTROPODA 119 
it is inside the pulmonary cavity (Fig. 174); m other forms with an 
aerial lung it is external (Fig. 89, 0s). 
Cyathiform bodies or gustatory bulbs, formed of taste-cells, are 
found on the lateral and ventral surfaces of the buccal cavity in 
sundry Rhipidoglossa, and at the sides of the buccal aperture in 
some Heteropoda. Analogous bodies have been found on the 
epipodial tentacles of Rhipidoglossa. 
The Otocysts, or statocysts, are hollow spherical vesicles, whose 
internal walls are lined by a ciliated epithelium containing sense- 
cells. These vesicles contain a liquid secreted by their epithelial 
walls, and in this liquid are calcareous auditory concretions of 
crystalline structure. There is a single large and spherical con- 
cretion or otolith in the more specialised Tectinibranchs and in a 
few adult Opisthobranchs (Loliger, the Elysiomorpha, Hedylidae, 
Pseudovermis, Fiona, and sundry Eolidomorpha), (viz. the Tergipedi- 
nidae, Cupellinia, Eolidiella, Eolis auwrantiaca and £. olivacea, Galvina 
picta and G. exigua). There are numerous and usually ovoid and 
elongated concretions, called Otoconia, in the Aspidobranchia (except 
Bathysciadium), in some of the less specialised Taenioglossa, such 
as Paludina, Ampullaria, Cyclophorus, Valvata, Nassopsis, and the 
majority of the Melaniidae, and in the Euthyneura in general, 
with the exception of the Opisthobranchs mentioned above. Oto- 
conia sometimes coexist with an otolith in certain Cerithiidae, 
Turritella, Doto, and Oncidium, but in all larvae there is only a single 
otolith (Fig. 116, A, III). Otocysts are absent in the adult Vermetus 
and in some Janthina. In creeping Gastropods the otoliths are 
situated in the foot, in the neighbourhood of the pedal ganglia (Fig. 
93, V), and are often adherent to these nerve-centres. In swimming 
Gastropods, such as Heteropoda, Phyllirhoc, and Glaucus, they show 
a tendency to approach the cerebral centres, and the same tendency 
may be seen in the majority of Nudibranchs. In all cases the 
otocysts are innervated from the cerebral ganglion, as may be most 
clearly seen when they are at some distance from the pedal ganglia 
(Figs. 123, C, of; 142, wu; 146, of). The neuro-epithelial elements 
are concentrated in a macula acustica, placed opposite the expansion 
of the otocystic nerve, in the otocyst of Heteropoda. 
Cephalic eyes exist in almost all Gastropods, and there are, in 
addition, pallial eyes in certain Oncidiidae. The two cephalic eyes 
are situated on the tentacles, in the Euthyneura on the posterior pair 
of tentacles. In the Streptoneura these eyes are placed at the outer 
side of the base of each tentacle, and are borne on tubercles (Fig. 
44, A, c) which may fuse with the tentacles, and thus, in a number 
of instances, give the eyes the appearance of being placed half-way 
up the tentacles, as may be seen in the Potamidae among the Ceri- 
thiidae, in Cypraea, many Rachiglossa, certain species of Conus (Fig. 
144, V), and Plewrotoma: in the last named they are very near the 
