ALIMENTAKY SYSTEM — INTESTINE. 
281 
ill most of the tissues of many mollusks, but is more especially fouml 
ill the digestive gland, making its aiiiiearance therein about 17 
hours after feeding and disappearing entirely after one to three days’ 
festing. It forms I'To per cent of the digestive gland in Heliv 
pninati((, decreasing during liibernation to 0'429 per cent. It would 
appear to be formed more especially from starchy food and is probably 
a respiratory fuel substance, as it disappears from the blood after its 
oxygenation in the respiratory organs, and is present in the muscles 
ill a ratio inverse to their activity. 
The Intestine, or gut, which arises at the stomach and terminates 
at the anus, has its inner epithelial layer overlaid by a him of closely 
adherent connective tissue, with 
numerous glandules together con- 
stituting the mucous membrane. 
Exterior to this comhined layer is 
the muscular stratum, whose con- 
tractions serve to impel the food on 
its course through the digestive 
canal. The intestine is greatly varied in its length and mode of 
convolution in the different groups and even in the different species, 
but there is no distinct division into large and small intestinal tracts 
as in the vertebrates, although the relative size of the parts may be 
reversed in many species, the pyloric end being often the largest. 
Fig. 557. — Ciliated and other cells from 
the lining membrane of the intestinal canal 
of Helix aspe7-sa Midi., highly magnified 
(after Howes). 
The two largest were actively secretory. 
Fig. 558. 
Fig. 559. 
Fig. 560. 
Fig. 561. 
Figs. 558-561. — Diagrammatic figures showing the mode in which the chief intestinal flexure 
has originated (after Butschli). st. stomach ; a. anus; r.g. right gill ; l.g. left gill ; //. heart. 
The spiral twisting undergone by the visceral sac of most Gastro- 
pods during the progress of body torsion, has necessarily involved 
in its movement the intestinal canal and other organs contained 
therein, and it is remarkable that in some of our nude forms, as 
the genera Amalia and Avion, the whole of the intenial organs 
