50 Laboratory Guide in Zoology 



parts — a small anterior part, the prostomium, a large 

 posterior part, the peristomium. Make careful draw- 

 ings of the upper and lower views of the head and the 

 first three segments back of it. 



IV. — Study the prostomium. Is it distinctly differentiated 

 from the peristomium ? Notice the central lobe bear- 

 ing in front the two club-shaped tentacles. Are they 

 segmented ? See on each side of this central lobe the 

 large conical palpi, distinctly segmented. Find the 

 small black spots which are the eyes. How many are 

 there ? 



V. — Study the peristomium : on each side in front are the 



two cirri, each double. Find the mouth. Sometimes 

 this is extended and shows the two black, serrated 

 mandibles. 



VI. — Study the lateral appendages of the body segments, 

 — ^they are the parapodia. Are they of the same size 

 throughout the length of the animal.-' Remove with 

 forceps one of the parapodia, and examine it with a 

 low magnifying power — a simple lens will do. Dis- 

 tinguish two general parts — the dorsal and ventral 

 lobes. On which is a large subtriangular blade — the 

 gill .'' Which bears the most spinose setae .'' Treat a 

 parapodium with caustic potash solution to bring out 

 the spinose acicula. Make a careful drawing of a para- 

 podium showing its parts and its basal connections. 



VII. — Lay the worm on the -bottom of the dissecting tray, 

 ventral side down. Cut longitudinally along the median 

 dorsal line, and pin down the cut edges on each side. 

 See how the body cavity is segmented. 



VIII. — Study the alimentary canal: see how the mouth 

 opens into the pharynx, which in the living worm can 

 be protruded; and how the pharynx leads into the 



