The Tanganyika problem; an account of the researches undertaken concerning the existence of marine animals in Central Africa . Fig- 34-—Semi diagram of the anatomy of Nassopsis nassa. Themantle has been cut open from above, and the nervous system isseen from above in black. Opposite sin., the gill ; cryst. s.,crystalline style ; sp. r., spiral caecum ; si., stomach. of several Littorinas. The oesophagus is long, narrow,and simple, and leads into a large stomachic chamber, onthe walls of which there are numerous glandular folds,and a very curious and striking spiral caecum on the 252 THE TANGAN
The Tanganyika problem; an account of the researches undertaken concerning the existence of marine animals in Central Africa . Fig- 34-—Semi diagram of the anatomy of Nassopsis nassa. Themantle has been cut open from above, and the nervous system isseen from above in black. Opposite sin., the gill ; cryst. s.,crystalline style ; sp. r., spiral caecum ; si., stomach. of several Littorinas. The oesophagus is long, narrow,and simple, and leads into a large stomachic chamber, onthe walls of which there are numerous glandular folds,and a very curious and striking spiral caecum on the 252 THE TANGANYIKA PROBLEM. floor, between the folds of which the curiously rectangularorifice of a single bile duct opens. Besides this stomachicchamber there is an anterior diverticulum into which thelarge stomach opens by a tubular aperture, through whicha bristle may be passed, and in this anterior stomachicchamber there lies an almost spherical crystalline Fig- 35-—The animal Nassopsis nassa from the dorsalaspect. The mantle has been cut open from above,and the radular sac exposed. The intestine passes out of the stomach beneath the tubularaperture between the posterior and anterior stomachicchambers, as indicated in the drawing on page 251. Theintestine is coiled in the manner seen on page 251, andtowards its rectal extremity it contains a number ofglandular folds and striae. The liver is large, and occupies the lower two-thirds of THE TANGANYIKA PROBLEM. 253 the last two whorls of the animals body. There is a singlebile duct, opening, as has already been stated, in the posteriorchamber of the stomach. The heart has the normal taenioglossate characters, andconsists of a thin-walled auricle, a thick-walled ventricle, anda short aortic trunk. Between the auricle, ventricle, andaortic trunks there are the usual valves. The gill ofNassopsis is of average length, very simple in structure, andconsists of a large number of low, broad, trian
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