KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3. 71 



their turn communicate with the posterior lacunae of the visceral hump by means 

 of a vessel beneath the pericard. From the renal sinus there emanates on the other 

 hand the marginal vein of the posterior demi-branch. 



The complete circuit of the blood thus takes place as follows: From the bran- 

 chiae the arterial blood is pumped by the action of the heart into the efferent vessel 

 of the branchial axis, which debouches into the auricle, after the reception of a 

 dorsal branch from the upper part of the branchial axis. From the auricles the 

 blood arrives into the heart and from there, by means of the anterior and posterior 

 arteriae, into the different parts of the body. It accumulates in the venous lacunae 

 and is carried away from them through the intravisceral veins mentioned. The 

 marginal veins carry the blood to the margin of the reflected lamella and the axial 

 vein communicates with them below. By the venous interlamellar septa the afferent 

 vessels discharge their blood into both lamellae of the demi-branchs, so that in the 

 gill of the Ghamidae a much more complicated blood circuit takes place than in 

 forms such as V nio with unplicate synaptorhabdic branchiae (ef. the preceding chapter). 



The strueture of the heart and the position of the valvulae in Chamidae is 

 described in detail by Grieser in 1913 for Ch. pellucida, and nothing need be added 

 with regard to this. 



3. The digestive system. 



All the species studied in this work have a very simple digestive canal. This 

 is formed in all cases by a short oesophagus followed by a stomach with various 

 coecal appendages and Ii ver duets. Beneath its fundus there follows a contracted 

 duodenal portion divided into two semi-tubular cavities, one of them being the reai 

 intestinal channel and the other the homologon to the coecum containing the cry- 

 stalline stylet that is still in intimate connection with and not perfectly differentiated 

 from the intestinal portion (on this question see further below). The duodenum 

 passes below through a sharp curve into the intestine proper, which may run more 

 or less in an S-curve through the body; it pierces the heart, behind which it pro- 

 ceeds as rectum to the anal siphon. A colon or widened median part of the intestine 

 may or may not exist. 



Differences between the species consist in the position and perfection of the 

 coeca as well as of the curvation of the intestine, which may or may not form a 

 flexure towards the front. These differences, however, as well as the more or less 

 complete presence of a colon, may perhaps be results of variation. 



With regard to the coecal appendages of the stomach a short or sometimes 

 rather produced posterior one is always present except in Pseudochama pusilla. All 

 of the forms of Chama have a peculiar finger-shaped coecal appendage on the left 

 side of the stomach produced towards the front and tapering. It is lined by the 

 same thick epithelium as the stomach, thus differing from the liver duets, which 

 have a lower epithelial lining. Grieser, who has observed this feature in Ch. pel- 

 lucida, states clearly that in this form it emanates from the right side of the stomach, 



