16 



G. After turning the right seminal vesicles to one side and observing the three 

 cesophageal calcareous glands (12th and 13th segments) ; the lateral blood 

 vessels joining the sub-intestinal vessel; and the pharyngeal plexus formed by 

 the breaking up of the longitudinal vessels ; carefully turn aside the portion 

 of the alimentary canal exposed, and fix to the left of the middle line. 



1. Examine the nervous system, noting the small nerves running forwards 



from the supra-cesophageal ganglia towards the prostomium, the 

 lateral commissures passing downwards to the ventral nerve-cord, so 

 as to complete the nerve ring, and the ventral cord formed by a pair 

 of fused ganglia in each segment from the fourth backwards connected 

 by a pair of united commissural cords. 



2. Continue the examination of the genital organs, noting at each side of 



the nerve-cord — 

 (a) The two pairs of spermathecse (betwcjen the 9th and 10th, 



10th and 11th segnients). 

 (6) The two small ovaries (one near each side of nerve-cord in 13th 



segment). 



(c) The oviducts which open internally in 13th segment, and exter- 



nally through 14th segment. 



(d) The two pairs of small testes (front of 10th and 11th 



segments), and the seminal ducts which have four rosette-shaped 

 ciliated internal openings (two in the 10th and two in the 

 11th segment), and two external openings in the 15th 

 segment, — testes only visible when seminal vesicles are small. 



3. Make an enlarged drawing (4 nat. size) shewing the genital organs and 



the exposed portion of the nervous system. 



H. Eemove the ovary and oviduct from one side, and examine with low power 

 in salt solution. 



(1) Sketch the pear-shaped ovary and the ripe and unripe ova in its 



interior. 



(2) Sketch the trumpet-shaped oviducts indicating their wide ciliated 

 internal openings into which the ova find their way on escaping 

 from the ovary. 



