ANODONTA — CIRCULATORY SYSTEM. 
173 
ning parallel to the postero-dorsal margin of the .shell above the 
posterior adductor and terminating in the shallow cloacal cavity of 
the snpra-branchial chamber. 
The whole intestinal tract is lined by ciliated and glandular 
columnar epithelium, the absorptive surface being greatly increased, 
especially in the first and the terminal tracts, by the presence of the 
typhlosole, an internal, thick, yellow, longitudinal ridge, formed by 
a strong infolding of the ventral walls. 
The digestive gland or liver is a somewhat symmetrical multilobed 
and greenish-brown organ, composed of numerous brown branched 
Fig. 340. — Tubule of Liver or digestive 
gland of Anodonta anatina, highly magnified 
(after Vogt and Yung). 
cu. cuticle ; en. endothelium ; i.c. lime cells? 
containing numerous refractive corpuscles? 
some enclosing pigment granules. 
Fig. 341. — Some elements of the liver of 
Anodonta anatina, isolated and highly 
magnified (after Vogt and Yung). 
tubules, with hepatic, ferment and lime cells, as in Helix, and lined 
with glandular cuboidal epithelial cells, with brown granular contents. 
It opens into the stomach by two large and several smaller ducts. 
As in Helix, the secretions probably change starch to sugar, i)roteids 
to peptones, and emulsifies the fatty foods. 
The Circulatory system is, as in Helix, composed of definite 
arterial and venous vessels and of an inter-communicating system of 
lacunar spaces. The heart, the pulsatile centre of the circulation, is 
a yellowi.sh sac placed near the hinge of the shell, within the spacious 
and elongate pericardium, and is formed of a median ventricle and 
two symmetrical and laterally disposed auricles. 
The auricles are paired, triangular, thin and somewhat transparent 
sacs, with their apices attached to the opposite sides of the ventricle, 
the broad basal ends receiving the blood aerated within the branchife 
and pallial lobes of their respective sides, which they transmit to the 
