290 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



organs, e.g., the nephridia. In this case the reproductive 

 products should be carefully washed away. A change of 

 sea water in the dish may even be necessary. 



The internal organs may be examined in the following 

 order : — 



I. Ccelom (see p. 231). 



II. Musculature. — Note the longitudinal and circular 

 muscles, the muscles of the pharynx, the setal muscles, the 

 oblique muscles, the three anterior septa, the two pouches 

 on the first septum, the rudimentary septa (the safety cord 

 accompanying the afferent vessel of the fourth nephri- 

 dium, and the small septa in two or three of the posterior 

 branchial segments), the caudal septa, the mesenteries of 

 the first and second segments. 



III. Alimentary Canal. — Note the proboscis, 

 pharynx, oesophagus, oesophageal glands, stomach covered 

 with the vessels of the gastric plexus between which are 

 the areas of chlorogogen cells, intestine, anus. Later 

 (after section V.) the stomach and intestine may be slit 

 open and their contents washed out so as to show the 

 ventral ciliated groove and the subsidiary grooves. The 

 stomach and intestine may be pushed over to one side, 

 care being taken not to break any of the blood-vessels, so 

 as to leave the greater part of the body wall in this region 

 open to view. 



IV. Yascular System. — Note the dorsal, intestinal, 

 gastric, oesophageal, ventral, sub-intestinal, neural, 

 nephridial longitudinal and dorsal longitudinal vessels, 

 the afferent and efferent vessels of the nephridia and gills 

 and the hearts. The sub-intestinal vessels are difficult 

 to see, and are only visible on carefully drawing the ventral 

 vessel a little further away from the wall of the stomach. 

 Note the chlorogogenous tissue on the ventral vessel. 



V. Nephridia and Gonads. — Look out for any 



