THE TANGANYIKA PROBLEM. 



253 



the last two whorls of the animal's body. There is a single 

 bile duct, opening, as has already been stated, in the posterior 

 chamber of the stomach. 



The heart has the normal taenioglossate characters, and 

 consists of a thin-walled auricle, a thick-walled ventricle, and 

 a short aortic trunk. Between the auricle, ventricle, and 

 aortic trunks there are the usual valves. The gill of 

 Nassopsis is of average length, very simple in structure, and 

 consists of a large number of low, broad, triangular leaves, 

 the apices of which are not produced into filamentous pro- 



Fig. 36.— The lingual dentition of Nassopsis nassa. 



cesses, nor ornamented in any way. The osphradium is 

 long and simple ; it lies in a groove at the base of the gill, 

 and shows no tendency to become pectinated or modified in 

 any way either before or behind. 



The nervous system of Nassopsis (Fig. $7) ls extremely 

 interesting, being one of the most archaic taenioglossate types 

 at present known. The cerebral ganglia are widely separated 

 from one another, and the pleural ganglia are not only 

 separated from the cerebral ganglia, but on the sides of the 

 oesophagus, the cerebro-pleural connectives being conse- 

 quently of considerable relative length. The supra-intestinal 

 cord springs directly from the right pleural ganglion, passes 



