VI PRACTICAL DIRECTIONS 355 



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 amoeboid corpuscles. 

 Sketch at intervals. (The small granules you will notice 

 in the ccelomic fluid are derived from the broken down 

 ye" low 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 ccelome : note the septa con- 

 necting the body-wall with the intestine. Then insert more 

 pins, obliquely, so as to expose the ccelome and enteric canal 

 up to the anterior end, liking especial care not to tear the 

 ventral parts of the septa and to stretch the animal longitud- 

 inally 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 Liimbricus, you will notice that the two anterior 

 pairs and the posterior pair 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 ; e. gizzard ; and /. 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 forceps, and cut 

 around the nephridium with the small scissors) mount in 

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

 and then with the high power. Note that the nephridium 

 consists of a long, coiled tube, plentifully supplied with 

 blood-vessels, and that long vibratile cilia can be seen in 



A A 2 



