8 EARTHWORMS AND THEIR ALLIES [ch. 



the case with the septa which separate segments v to 

 xii. The alimentary canal is perfectly straight and 

 runs in the middle line, being supported by the septa 

 which it perforates. The mouth leads into a buccal 

 cavity which later becomes the pharynx, a portion of 

 the tube which is much thickened by muscular walls 

 dorsally. Then follows a very short section of the 

 oesophagus and in the fifth segment this becomes 

 the gizzard, a very characteristic organ with thick 

 muscular walls quite smooth and Avith a very thick 

 lining of structureless membrane. After this is a 

 narrower tube, the rest of the oesophagus. Into this 

 open in each of segments vn, viii, ix a pair of cal- 

 ciferous glands ; these are diverticula of the gut with 

 much folded walls, the cells of which secrete carbonate 

 of lime. In the xnth segment or so, the oesophagus 

 suddenly widens out to form the intestine which runs 

 as such to the end of the body. This wider tube has 

 a ridge running along its dorsal side, the typhlosole. 

 Along the dorsal surface of the intestine and the oeso- 

 phagus is seen a red tube, contractile during the life 

 of the worm, which is the dorsal blood vessel and 

 whose contained blood is coloured red, as is the blood 

 of vertebrated animals, by haemoglobin. But in the 

 earthworm the colouring matter is not situated in 

 corpuscles as in the vertebrate. The dorsal vessel is 

 connected by a few pairs of equally contractile trans- 

 verse trunks with a ventral vessel which is not 



