192 SEGMENTED WORMS OR ANNELIDA. 



Alimentary System. 



Earthworms eat the soil for the sake of the plant 

 debris which it may contain, and also, indeed, because 

 they must swallow as they tunnel. In eating they are 

 greatly helped by the muscular nature of the pharynx, 

 whence the soil passes down the gullet or oesophagus, first 

 into a swollen crop, then into a strong walled grinding 

 gizzard, and finally through a long digestive and absorptive 

 stomach intestine. On the gullet are three pairs of ceso- 

 phageal or calciferous glands the products of which are 

 limy and able to affect the food chemically, probably 

 counteracting the acidity of the decaying vegetable matter. 

 The long intestine has its internal surface increased by a 

 dorsal fold, which projects inwards along the whole length. 

 In this " typhlosole," and over the outer surface of the gut, 

 the yellow cells are crowded. There is no warrant for 

 calling these hepatic or digestive. Structurally they are 

 pigmented cells of the peritoneal epithelium, which here, as 

 in most other animals, lines the body cavity and the outside 

 of the gut. As to their function we know that they absorb 

 particles from the intestine, and go free into the body cavity, 

 whence, as they break, up, 4heir debris may pass out by the 

 excretory tubes. When a worm has been made to eat 

 powdered carmine, the passage of these useless particles 

 from gut to yellow cells, from yellow cells to body cavity, 

 and thence out by the excretory tubes, has been traced. 

 Various ferments have been detected in the gut, a diastatic 

 ferment turning the starchy food into sugars, and others 

 peptic and tryptic not less important. The wall of the 

 stomach intestine from without inwards, as may be traced 

 in sections, is made up of pigmented peritoneum, muscles, 

 capillaries, and an internal ciliated epithelium. In the other 

 parts of the gut the innermost lining is not ciliated, but 

 covered with a cuticle. 



Vascular System. 



The fluid of the blood is coloured red with haemoglobin, 

 and contains small corpuscles. Along the median dorsal 

 line of the gut a prominent blood vessel extends, 

 another (supra-neural) runs along the upper surface 



