56 NILS HJ. ODHNER, STUDIES ON RECENT CHAM1DAE. 



the posterior gill was completely attached on the left, only below on the riglit 

 side. 1 



The foot is short and broad (its length is a little greater than its breadth) 

 and is situated at a distance from the mouth of about its own length. Behind it 

 there follows a short pouch and then the triangulär lobe. 



Internal anatoniy. 



The intestinal canal (fig. 69). Somewhat behind and above the inner mouth 

 of the oesophagus the stomach has a transversal extension, and its left corner is 

 produced into a finger-shaped coecal appendage directed forwards and somewhat 

 upwards and lined with the same cylindrical ciliated epithelium as the stomach. 

 This coecum debouches just above the level where the upper wall of the oesophagus 

 passes into the stomach. Outside this coecal appendage there appears a large liver 

 duct which descends from the left umbonal liver folliculi; it opens into the sto- 

 mach at the side of the oesophagus, and some smaller ones lie close by. Some- 

 what below the cardia liver ducts open both on the left and right side into the 

 foremost part of the stomach. The liver ducts are, consequently, divided throughout 

 their whole extent into a left and a right trunk; of these the left one penetrates 

 most deeply and represents the principal liver canal of the Chamidae in general. 

 Both the left and the right canals were filled with nutritive matter. Just above 

 their junction with the stomach this detaches from its right posterior wall a short 

 and wide hanging coecal sac. The stomach also receives some more liver ducts on 

 the right side. Below it passes into the duodenum, which is divided into a narrow 

 furrow on the right and a larger one on the left; below they attain a uniform width 

 and pass into the intestine with a curve forwards and upwards. The latter keeps 

 about the same width troughout, and having passed through the heart, proceeds on 

 the hinder side of the adductor posterior. 



The circulatory system (fig. 69). Aorta anterior, as usual, splits into t\vo 

 trunks, of which the dorsal one passes into the mantle and runs forward to the left 

 side of the oesophagus, where it descends into the foot as the arteria pedalis; the 

 ventral trunk follows the intestine downwards to the left side of the duodenum, 

 which it encloses from behind by bifurcating. 



The nervous system is of the usual type; its cerebro-visceral connectives 

 run at the left side close beneath the surface of the body, on the right side they 

 go much deeper between this and the stomach. In their frontal part they penetrate 

 the liver, in the posterior half they lie outside it. The left cerebro-visceral con- 

 nective describes a wide curve upwards as a consequence of the elevation of the 

 left umbo. 



The gills ha ve from 20 to about 30 filaments in each fold. They are con- 

 structed chiefly as in Ch. julcesi. No axio-marginal connections exist. 



1 Poli (1791) represents in pl. XXIII, fig. 4, the inner margin of the right gill as free from the hody; 

 posteriorly the tips of the gills are apparently fixed to the circumsiphonal muscles of the mantle. 



