vi PRACTICAL DIRECTIONS 357 



IV. Remove the sperm-sacs carefully, and make out further details 

 as regards the enteric canal (see II. 2). Note the oesophageal pouches 

 and glands. Cut open part of the intestine along one side, and observe 

 the thick dorsal fold or typhlosole projecting into it. Sketch. 



V. i. Note the small cerebral ganglia or brain on the dorsal side of 

 the buccal sac, and then cut through the anterior part of the pharynx 

 just behind the brain. Carefully remove the enteric canal, noting as you 

 do so the ventral sub-intestinal blood-vessel. The nervotis system will 

 now be exposed. Observe again the paired cerebral ganglia, from 

 which arise a pair of connectives^ forming a small nerve-ring or collar 

 around the buccal sac, and continuous ventrally with the ventral nei~ve- 

 cordj consisting of fused lateral halves and extending along the whole 

 length of the ventral body-wall, passing through a perforation in each 

 septum, and expanding slightly in each segment, so as to form ganglionic 

 swellings. Three pairs of nerves are given off in each segment. 

 Sketch. 



2. Remove the nerve-ring and a small portion of the ventral cord, 

 and examine with the low power. Sketch. 



3. A lateral neural vessel can be seen close to the ventral cord on 

 either side. . Remove a portion of the cord, and note the sub-neural 

 vessel. 



VI. Further details as regards the structure of the nephridia are best 

 made out on a worm which has been preserved in spirit. Very care- 

 fully remove the enteric canal as directed above, so as not to injure the 

 septa more than necessary : the nephrostomes can then be seen with a 

 lens, looking like small, whitish dots. Remove an entire nephridium 

 carefully as before ( II. 4), stain, and mount in glycerine or balsam. Note 

 the three loops, and a. the ciliated nephrostome ; b. the first, slender 

 part of the tube with its cilia ; c. the second, wider, ciliated part ; 

 d. the third, still wider, glandular part ; and e. the fourth, much wider, 

 muscular part which opens on to the exterior by the nephridiopore. 

 Sketch. 



VII. Remove a small piece of the integument containing seta, and 

 separate the latter out with needles. Mount in water and examine. 

 Sketch. 



C. Transverse Sections. For the preparation of these, keep a 

 worm for a few days in coffee-grounds or small pieces of blotting-paper 

 moistened with water, in order that the gritty contents of its intestine 

 may be replaced by a soft substance which will not blunt the razor. 



