43 



HIRUDINEA 



2. The Leech opened by a median dorsal incision extending from the posterior sucker to the 

 prostomium. The eleven pairs of alimentary caeca (belonging to the same segments, respectively, 

 as the 4th i4th post-oral ganglia); vessels (dorsal and lateral trunks) containing blood coloured 

 red with haemoglobin. Median rectum corresponding to the last eight ganglia ; rectal caeca ; anus ; 

 seventeen pairs of nephridia existing in the same segments as the 2nd to the i8th post-oral nerve 

 ganglia inclusive, though the first is in the same horizontal line with the third post-oral ganglion. 



3. Remove the alimentary canal and expose the nephridia, generative organs and nerve-cord. 

 The nine pairs of testes, the first lying in the same segment as the 8th post-oral ganglion, and 

 between the 6th and 7th pairs of nephridia; the epididymis on each side in the 7th post-oral; 

 the vas deferens on each side ; the penis opening in the middle line behind the 6th post-oral 

 ganglion ; the pair of ovaries ; the glandular enlargement of the oviducts (albumen gland) ; the vagina 

 opening in the middle line behind the seventh ganglion ; the seventeen pairs of nephridia numbered ; 

 the twenty-three post-oral ganglia of the nerve-cord ; the supracesophageal ganglion ; cesophageal 

 passage between the cerebral ganglion and the ist post-oral ; the double nerve-cord enclosed in 

 ventral sinus. 



