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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. Coelom (see above). 
II. Musculature.—Note the longitudinal and cireular 
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 afterent 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, esophagus, esophageal 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. Vascular System.—Note the dorsal, intestinal, 
gastric, cesophageal, 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. 
\Y. Nephridia and Gonads.—Look out for any 
