vi PRACTICAL DIRECTIONS 355 



B. Dissection-: 



I. Take a freshly-killed worm in the left hand, and carefully insert 

 the point of the fine scissors into the integument about one-third of the 

 way along the body, close to the middle dorsal line. Place a drop of 

 the ccelomic fluid which exudes on a slide, add a drop of salt solution, 

 and cover. Examine with the low and high powers, and note the 

 structure and movements of the ama-boid corpuscles. Sketch at 

 intervals. (The small granules you will notice in the ccelomic fluid are 

 derived from the broken down yellow cells of the intestine. ) 



II. Continue the cut forwards to the prostomium, keeping very slightly 

 to one side of the median dorsal line, and taking care that the point 

 of the scissors does not penetrate deeper than the integument : note the 

 iridescent cuticle. Place the animal in a dish with just enough water 

 to cover it ; and carefully insert a pin between the integument and the 

 yellow intestine on either side, near the posterior end of the incision, 

 so as to expose the calome : note the septa connecting the body- wall 

 with the intestine. Then insert more pins, obliquely, so as to ex- 

 pose the ccelome and enteric canal up to the anterior end, taking 

 especial care not to tear the ventral parts of the septa and to stretch 

 the animal longitudinally as much as possible. Then note : 



1. The sperm- sacs three or four pairs of large white bodies in 

 segments IX-XII, and varying greatly in size and form according to 

 the size of the animal. If your specimen is an adult Lumbricus^ you 

 will notice that the anterior and the two posterior pairs are respectively 

 united across the middle line, beneath the enteric canal, to form 

 the two sperm-reservoirs. 



2. The enteric canal and its subdivisions : a. buccal sac ; b. 

 pharynx ; c. gullet (largely hidden by the sperm-sacs) ; d. crop : 

 gizzard ; and e. intestine ', covered with a layer of yellow cells. 



3. The dorsal blood-vessel, containing red blood and giving off 

 branches to the enteric canal ; the large rhythmically contractile 

 commissural vessels connecting the dorsal with the ventral (sub-intestinal) 

 vessel : the latter will be seen subsequently. 



4. A pair of small, whitish, coiled bodies, the nephridia> attached to 

 the posterior face of each septum exposed (except the first three), on 

 either side of the enteric canal. Carefully remove one of these in 

 the region of the intestine -(take hold of the septum with the fine for- 

 ceps, and cut around the nephridium with the small scissors) mount in 

 salt-solution or water, and examine first with the low power, and then 



A A 2 



