32 LAND AND FRESH-WATER SHELLS 



precipitate any proteids that may be present in solution, and this 

 is continued until no precipitate any longer obtains. Then it 

 is filtered — if any glycogen be present the filtrate is clear and 

 opalescent — and the glycogen is precipitated firom the filtrate by 

 adding 70 to 80 per cent, of alcohol in excess. The precipitate 

 obtained is then washed with 60 and 90 per cent, of alcohol, 

 afterwards with ether, lastly with absolute alcohol, then 

 dried over sulphuric acid and weighed. Claude Bernard (born 

 1813, died 1878), a great French physiologist, was the first to 

 discover this substance in the liver-cells of the Vertebrates and 

 the Mollusca ; he published his researches in 1857. Besides 

 being known under the name of glycogen, it is often spoken 

 of as hepatine, benardine, and zoamyline or animal starch. 



The Circulatory System. — The fluid in the Mollusca which 

 corresponds to the blood of the higher animals is known as blood- 

 lymph or h^molymph. In it white-corpuscles or lymph-corpuscles 

 float. In Helix the ha^molymph contains a respiratory substance 

 termed h?emocyanin, which contains copper united with a proteid, 

 and turns bright blue, when oxidised ; in Planorbis corneus it 

 contains haemoglobin. The heart is surrounded by a pericardium, 

 and situated near the kidney or nephridium in the dorsal portion 

 of the body-cavity. The pericardium communicates with the 

 kidney by a ciliated tube — the reno-pericardial canal ox nephridial 

 tube. The heart is composed of an auricle and a ventricle, 

 separated from one another by an auriculo-ventricular valve. 

 The aorta arises from the base of the ventricle, and immediately 

 divides into an anterior and a posterior aorta. The anterior 

 aorta passes into the prostoma under the head of the spermatheca 

 and the first coil of the intestine, and ends in relation with the 

 undersurface of the buccal mass, giving branches on its way to 

 the foot, crop, salivary glands, tentacles, reproductive organs and 

 integument, and also special branches to the supra-pedal gland 

 and rectum ; the posterior aorta passes into the visceral hump, 

 and supplies the intestine, reproductive organs, and hepato- 

 pancreas. There are no special capillaries, and the blood passes 

 from the arteries into blood-spaces, — the transition vessels of 

 Nalepa, — from whence, after supplying nutriment to the tissues, 

 it is returned to the heart by way of the various venous sinuses. 



