276 
ALIiMENTAUV SYSTEM — SALIVARY GLANDS. 
In tlie Gastropoda, tlie salivary glands arise as simple outgrowths 
of the alimentary canal, and are i)aired foliaceons lohnlate organs, 
often fused together dorsally, composed of hranched hlind tubules 
lined with glandular epithelium and 
attached by connective tissue to the 
sides of the msophagus or to the walls 
of the foregut or crop, and though 
there is a general resemblance in this 
organ among the different species, 
yet there are some divergent forms, 
the most striking example being 
Ci/closfonia elegaua, whose 
glands in their natural position are 
curiously coiled up, hut when un- 
folded resemble the handles of church-hell ropes. 
'I'he secretory cells are large and somewhat oval, with large oval 
nuclei, which can he rendered visible by reagents ; they are invested 
by connective tissue, containing free nuclei. The secretions escape 
from the individual cells by the rupture of 
their investing ti.ssue, and are gathered 
eventually into the usually darkly i>ig- 
mented common ducts of each gland, 
which are placed at each side of, and 
acconqianying the (esoi)hagus through the 
nerve ring, and convey the fluid into 
the in)i)er part of the Imccal cavity, where 
it is discharged by enlarged outlets. 
The constituents of the salivary secre- 
tions differ in the different groups, some 
marine genera even .secreting sulphuric 
or hydrochloric acid, hut the Gastroiioda of our country usually 
secrete a ferment which, in addition to mixing with and moistening 
the food and thus assisting its passage along the digestive canal, also 
converts the starch of the food into glucose or sugar. In our 
branchiate .species these .secretions have been a.scertalned to con- 
tain Calcium, Mucin, Sulphocyanate and Calcium-pho.sphate, and 
l)ossihly a trace of Chlorine, while in the Pulmonates, Calcium and 
Chlorine are the chief constituents, l^uliihocyanate and Calcium- 
pho.sjdiate being doubtfully pre.sent. 
Fit,. — Transverse section 
through Salivary gland to show the 
arrangement of the cells, highly 
magnified (after Vogt and Viing). 
sl.c. nucleated salivary cells ; c.c. 
scattered connective tissue cells; <L 
lumen of duct of gland, showing 
some of the more minute duct end- 
ings; c/>. epithelium. 
(I 
Fig. 547. Fig. 548. 
Fig. 547. — Anterior part of cesophagus 
of Cychstoina t7ci.’n!//A OInll X X 3, show- 
ing the disposition of the Salivary glands. 
r.^. cerebral ganglia; s.i^. sali\ary 
glands ; a\ cesophagus. 
Fig. 5IS.-Salivary gland of Cyclosioma 
cU'gans (.Midi.) opened out. 
