64 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



hang down into the cavity of the ray, which they nearly 

 fill. 



With a knife or a pair of strong scissors cut through the 

 body wall for about an inch on each side of the ray, just 

 outside the inter-ambulacral ossicles, taking pains to avoid 

 injuring the soft parts. Lift up the ab-oral wall by its free 

 end, and carefully cut the mesenteric membranes which 

 bind the hepatic coeca to its inner surface. Repeat the 

 cuts in the same way until the roof of the ray has been 

 freed from tip nearly to base. Free the wall of the adja- 

 cent ray of the trivium in the same way. Lift up the 

 roof of the disc, and free it from its attachment to the soft 

 parts, nearly as far as the centre. Cut off and remove 

 the integument which has been loosened, thus exposing 

 the internal organs of the two rays and disc. Place the 

 specimen in a shallow, flat-bottomed dish, cover it with 

 water, or water and alcohol, and notice : — 



a. The large brown sacculated hepatic coeca (Fig. 

 30, b) ; two in each ray, reaching from the base nearly 

 to the tip. The dilations of the coeca are arranged in 

 pairs, and they hang down into the cavity of the ray. 



b. Near the base of the ray the sacculations disappear ; 

 the coeca suddenly constrict, and give rise to a pair of deli- 

 cate membraneous tubes (Fig. 30, «), which are attached, 

 like the coeca, to the inner surface of the body-wall, by 

 mesenteric membranes. 



The two tubes soon unite to form a common duct, which 

 can be traced into the disc. 



c. The proximal ends of these ducts open into a large 

 pentagonal membraneous pouch, the pyloric sac of the 

 stomach, which fills nearly the whole of the ab-oral portion 

 of the cavity of the disc, and which is attached to the 

 oody-wall along its edges by mesenteric folds. The angles 



