OF WORMS. 217 



end of the proboscis, but at its base, and exactly in the inferior 

 middle line of the body. Starting from the mouth with consid- 

 erable breadth (st), the digestive canal thins rapidly to a small 

 calibre, and winds in several overarching folds (i) alternately 

 from one side to the other, until it comes to a termination (a) at 

 the posterior end of the body. 



The respiratory organs, if such they may be called, are a 

 pair (figs. 126, 127, br l ) of spindle-shaped sacs, which are at- 

 tached on each side of the intestine, and open (at br) into it just 

 before its posterior termination (a). The whole surface of these 

 sacs is covered by branching tubes, which form so many pro- 

 longations from the main cavity upon which they are based. 



The circulatory system, owing to the enormous extensibility 

 of the proboscis, has a more complicated appearance than really 

 exists. That part of it which most probably corresponds to the 

 heart (h) lies in the posterior half of the body, above the intes- 

 tine, and is to be distinguished from the rest of the system by a 

 considerable thickening at that point, and a puckering of its wall. 

 From the heart the blood is impelled into a vessel (h l ) which 

 passes along the middle line of the body and proboscis to the 

 tip of the latter ; at this point (7/ 4 ) it divides right and left, 

 and follows the borders of the T-shaped part along the front 

 and then the back edge, and then courses on each side (A 3 , A 5 ) 

 of the main stem to the body. Passing on each side of and 

 below the gullet, close to the mouth, the vessels make a junction 

 (A 7 ) behind the latter, but immediately separate to form a ring 

 (/i 8 ) about the trumpet-shaped entrance (oy 3 ) of the emptying con- 

 duit, matrix, (ov 1 ,) of the reproductive organ, and then unite 

 again into a larger single vessel, which carries the blood along 

 the lower side of the body to the double posterior cavity of the 

 heart. From thence the blood passes upward and forward into 

 the main chamber (h) from which it started. If, now, we take 

 a foreshortened view (fig. 127) of this system, we shall see that 

 it is a mere ring about the intestine, with the heart, (h,) and its 

 anterior prolongation, above ; the two branches along the limbs 

 and stem of the T-shaped proboscis forming the two lateral 



