EXCRETORY SYSTEM. 77 



loop ; it then bends back sharply on itself, and 

 returns, following the same path, to the base of 

 the short loop, where it passes into the second 

 part of the tube. The duct of the * narrow tube ' 

 is an intracellular one, traversing the individual 

 cells, which are placed end to end like drain-pipes. 

 The * narrow tube ' is ciliated along part, but not 

 the whole of its length. 



c. The second part of the tube, or * middle tube,' 



forms the proximal limb of the long loop. The 

 duct is here also an intracellular one : it is much 

 wider than that of the ' narrow tube,' and is 

 ciliated along its whole length. 



d. The third part of the tube, or 'wide tube,' com- 



mences with a dilated part of the ampulla, at 

 the apex or bend of the long loop : beyond this 

 it forms the distal limb of the long loop, both 

 limbs of the short loop, and a portion of the 

 proximal limb of the terminal loop. The duct 

 in this portion of the tube is wide, intracellular, 

 and non-ciliated ; and its walls consist of very 

 granular protoplasm. 



e. The fourth part of the tube, or 'bladder,' forms 



part of the proximal, and the whole of the distal 

 limb of the terminal loop. It is much wider than 

 the rest of the tube ; it is lined by epithelium ; 

 and its walls, which are non-glandular, contain 

 interlacing muscular fibres. The ' bladder ' opens 

 to the exterior by the aperture already seen. 

 Its cavity contains parasitic round-worms, not 

 to be mistaken for cilia. 



E. The Reproductive System. 



The earthworm is hermaphrodite. The reproductive 

 organs are lodged in segments ix. to xv., i.e. in the region of 

 the oesophagus. 



H 



