24 



Cut across the pharynx near its centre, and the intestine near its termina- 

 tion, and carefully remove the intestinal tract, in order to expose the blood 

 vessels, nervous system, and the reproductive and segmental organs. 



Observe — 



(1) The ventral blood vessel enclosing the nerve cord and sending branches 



to communicate with the lateral blood vessels. 



(2) The segmental organs (17 pairs corresponding to the 2d to the 18th 



ganglia inclusive) consisting of convoluted tubes in connection with 

 rounded vesicles. 



(3) The 9 pairs of testes (corresponding to ganglia 8 to 16 inclusive) with 



their diicts opening into the two vasa deferentia, and that the vasa 

 deferentia become convoluted to form the large vesiculse seminalis 

 which communicate with the penis — the penis lies in a bent sheath 

 which, springing from a large sac, opens through the 24<th ring behind 

 the mouth. 



(4) The 2 small ovaries lying in the segment behind the vesictilee seminalis, 



which communicate by slightly twisted oviducts with a muscular 

 uterus — the uterus opening to the exterior between 29th and 30th 

 rings behind the mouth. 



(5) The 4 mucous glands, if visible, lying behind the ovaries. 



(6) The nerve cord extending backwards from the oesophageal ring to end 



in a large ganglion lying above the posterior sucker. Noting — 

 (a) The two supra-oesophageal ganglia giving off 5 pairs of optic 

 nerves and communicating with the 3 small buccal ganglia 

 which lie one above and one at each side of the buccal cavity. 

 (6) The commissures connecting the supra-oesophageal ganglia with 

 the sub-cesophageal ganglion, which is made up by the fusion 

 of 3 or 4 embryonic ganglia, and from which several (4) pairs 

 of nerves extend to the surrounding tissues, 

 (c) The 2d to the 21st post oral ganglia, each giving off 2 pairs of 

 nerves, the 22d ganglion giving off only 1 pair of nerves, and 

 the 23d (made up of 6 or 7 embryonic ganglia) giving off 7 

 pairs of nerves. 



(7) Examine with a low power and sketch a portion of the double nerve 



cord lying in the ventral blood vessel, and one of the ganglia with 

 its lateral branches. 



(8) Make a drawing, showing (a) the ventral and lateral blood vessels, (b) 



the.nephridia, (c) the generative organs and the nervous system. 



