ix PRACTICAL DIRECTIONS 429 



the mid-ventral line : the atrial epithelium is often much folded ven- 

 trally. 



4. The single ventral aorta in the endostylar coelomic canal, and the 

 paired dorsal aorta, on either side of the epibranchial groove. 



d. Note again a. 2, 3, 4, 5 ; c. I, 3, 4, and also : 



1. The pharynx, much as in c 2, but laterally compressed. The en- 

 dostyle is now converted into a groove. 



2. The hepatic cacum, on the right side of the pharynx, and covered 

 by the atrial epithelium. Note the ccelomic space around it, in which 

 are the portal veins and the hepatic veins (dorsal side). 



3. The gonads (ovaries or spermaries) large masses on either side of 

 the pharynx, projecting into the atrial cavity and covered by the atrial 

 folds. The spaces around them represent portions of the coelome. 

 Note the small sperm-cells in the male, and in the female, the large ova. 



(The nephridia can only be made out satisfactorily in good sections of 

 very w r ell preserved specimens. ) 



