ix PRACTICAL DIRECTIONS 42< 



ccflomic spaces on the outer sides of the rods; (d) the 

 dorsal suspensory folds of the pharynx, which enclose the 

 two dorsal ccelomic canals. 



3. The atrial cavity, surrounding the pharynx, except at 

 the mid-dorsal line, where the pharynx is attached to the 

 sheath of the notochord, and communicating with the 

 cavity of the pharynx through the gill-slits. It is enclosed 

 by the two atrial folds, which are united in the mid -ventral 

 line : the atrial epithelium is often much folded ventrally. 



4. The single ventral aorta in the endostylar ccelomic 

 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 : 



i. The pharynx, much as in c. 2, but laterally com- 

 pressed. The endostyle is now converted into a groove. 



z. The hepatic ccecum, 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 ccelome. 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 well preserved specimens.) 



E K 3 



