14 



C. ^ix the earthworm with the dorsal surface upwards by one pin through the 



1st, and another through the 50th segment, and cover with salt solution. 

 Cut along the middle, line from the 25th to the 1st segment, and fix back 

 the skin by introducing pins obliquely through the 3d, 7th, 12th, 16th and 

 20th segments. 

 Observe and indicate in a drawing (2 nat. size) — 



(a) The mesenteries (intersegmental muscular septa), and the segmental 



organs in connection with them. 

 (6) The supra-oesophageal nerve ganglia (3d segment). 



(c) The pharynx (1st to 7th segments) oesophagus (8th to 15th segments), 



and the calcareous oesophageal glands, proventriculus-(16th to 17th), 

 gizzard (18th), and the intestine, invested with buff-coloured pig- 

 ment, extending backwards from the 19th segment. 



(d) The bilobed anterior and the usually simple posterior seminal vesicles 



(9th to 12th segments). 



(e) The two pairs of spermathecse. 



(/) The dorsal vessel above the intestine, breaking up into a plexus over 

 the pharynx, and the dilated lateral vessels arching round the 

 intestine from the 8th to the 15th segments. 



D. With a pair of fine scissors remove one of the segmental organs. Mount in 



salt solution, and examine first with low and then with high power, noting 

 and drawing — 



(a) The ciliated funnel-shaped opening by which the segmental tube 

 communicates with the body cavity (ccelom), in front of the 

 mesentery. 

 (&) The narrow portion which pierces the mesentery, 

 (c) The coiled glandular portion behind the mesentery lined with cHiated 

 epithelium, and surrounded by capillaries in connection with the 

 dorsal and sub-intestinal blood vessels. 



E. Examine in salt solution, first with low and then with high power, a portion 



of a seminal vesicle. Note and draw — 



(a) Sperm-polyplasts in various stages of development. 



(6) Free spermatozoa — usually better seen in contents of spermathecse. 



F. In the same preparation look for and sketch, if present, the following stages 



in the life history of the gregarina of the earthworm (Monocystis lumbrici). 

 (a) Free gregarinse. 

 (6) Cysts containing — 



(1) Two entire gregarinse or a single gregarina. 



(2) Gregarinse partly broken up. 



(3) Pseudo-naviculse. 



