344 THE EARTHWORM chap. 



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 alimentary canal, noting as 

 you do so the ventral or sub-intestinal blood-vessel. The nervous-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 

 nerve-cord, consisting of lateral halves fused together and extending along 

 the whole length of the ventral body-wall, passing through spaces 

 in the septa, 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 (§ H. 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 ; t. 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 nephridiofore. 

 Sketch. 



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

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

 Sketch. 



C. Transverse Sections. — For the preparation of these, it is best 

 to keep a worm 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. 

 Kill the worm, cut a small piece about \ inch in length from the region 

 of the intestine,; ajid fix, stain, and cut into transverse sections ^s 



