ANNELIDA .- THE EARTHWORM, NEREIS ±1$ 



and lying end to end. The cilia set up a current which 

 sweeps in and carries off the excretory granules formed by 

 the yellow cells, together with substances taken from the 

 blood and excreted by the walls of the tubes. Some of these, 

 in the form of granules, colour the brown part of the tube. 

 Earthworms have no special respiratory organs, but an inter- 



FlG. 142. — A diagram of a nephridium of the earthworm. 



br.t.. Brown, ciliated tube; m.t., muscular tube; n.c.t., glandular, non-ciliated 

 tube; n.t., narrow tube, ciliated in parts; nst., nephrostome ; Sep., septum; 

 ves.tiss., connective tissue with vesicular cells and blood vessels; i, 2, 3, the 

 three banks of the tube. 



For details of structure see Plate XVII. 



change of gases with the air takes place in the skin, which 



is richly supplied with blood vessels. 



The blood of an earthworm is red on account of the 

 presence of haemoglobin, which is in solution, 

 not in corpuscles. Colourless corpuscles are 



present. The blood-vascular system is very complicated. 



Its main outlines are as follows. A large dorsal vessel 



runs the whole length of the body from the hinder 



Blood Vessel!. 



