GtrSTATORY ORGANS — ORGANS OF SEMPER. 
243 
In the Euthyneura the organs of Semper, although especially 
developed in the Arionidcv and Limacldw, are also present in the 
Stylonnnatophora generally, the lateral lobes receiving their innerva- 
tion from the cerebral ganglia, and the dorsal lobes, according to 
Hanitsch, receiving two small nerves from the bnccal ganglia ; each 
lobe possesses a small ganglion composed of small spherical ganglion 
cells, such as are found in the more specialized sensory regions of the 
Fig. 489. — Side view of buccal mass of 
Limax cinereo-ft2\^e7' Wolf, X 2, showing 
Semper’s organ (after Sochaczewer). 
Ij.b. buccal bulb ; c.g. cerebral ganglia ; 
y. jaw; i,n, labial nerve; i.t. lower tentacles ; 
O', oesophagus ; p.n. nerve piercing beneath 
side muscles of pharynx; s,d. salivary ducts 
s.gl. Semper’s organ ; t. tentacle. 
Fig. 490. — Longitudinal section through 
head of AgrioUynax agrestis (L.), X 20, 
showing Semper’s glands, gland cells and 
muscles (after Hanitsch). 
ep. epithelium ; g.c. gland cells; j. jaw ; 
m. muscle bundles ; s.^. glands of the organ 
of Semper, showing their unicellular character 
and independent ducts. 
cerebral ganglia. The epithelium of these special regions is excep- 
tionally thick, as in other sensory areas, and each lobe is moistened by 
a very fluid secretion from the cluster of somewhat pyriform cells they 
contain, each cell being furnished with a delicate duct with outlet upon 
special papilla) placed above the lateral lips at each side of the month. 
The Basommatophora, although possessing labial ganglia of homo- 
logous nature to those of the Stylonnnatophora, have not the 
distinctly lobulated lips characteristic of Semper’s organ. 
The presence of the unicellular glands, whose secretions impart the 
moistness to the gustatory tissues, has induced some observers to regard 
Semper’s organ as a buccal salivary gland, homologous with the anterior 
salivary glands found in certain other grou})S of mollusks. 
Simroth is of opinion that the sense of taste is concentrated in the 
front of the buccal cavity in land shells, but he has not detected this 
specialized region in aquatic forms, and concludes the sense is in 
them more diffused over the whole outer surface of the body. 
In the Pelecypoda the faculty is hardly developed, but may be 
exercised by the internal surface of the labial tentacles, which are 
richly innervated and act as guards to the month, though little dis- 
crimination ai)pears to he exercised in selecting food, almost anything 
small enough to enter the mouth being swallowed, 
