EXAMINATION OF UNIO OR ANODONTA. 



289 



II. The examination of a section between the posterior 

 adductor muscle and the heart. 



a. Notice the mantle cavity (Fig. 147, h, i, &), in sub- 

 stantially the same position as in the preceding section : 

 containing the gills (Fig. 

 147, I, m), and bounded 

 at the sides by the man- 

 tle lobes(a, a), andabove 

 by the body cavity. 



FIG. 147. Diagram of a 

 vertical section through the 

 body of Unio purpurea, be- 

 tween the heart and the 

 posterior adductor muscle. 

 (Drawn from nature by W. K. 

 Brooks. ) 



a, b, c, and h. as in Fig. 

 146. i, L Cloacal tubes of 

 outer gills. A;. Cloacal tube of 

 inner gills. I. Outer gills. 

 m. Inner gills. n. Outer 

 lamella of outer gill. o. In- 

 ner lamella of outer gill. 

 q. Outer lamella of inner gill. 

 r. Inner lamella of inner gill, 

 s. Retractor muscles of foot. 

 t. Glandular portion of organ 

 of Bojanus. 



FIG. 147. 



b. The body cavity is of about the same size as in the 

 previous section ; somewhat triangular in shape, and occu- 

 pying the dorsal portion of the section. 



1. On the median line of the body cavity, close to the 

 dorsal surface, notice the intestine (Fig. 147, p), with 

 horseshoe-shaped cavity and ventral ridge. 



(i.) The intestine is surrounded by a layer of connec- 

 tive tissue, which is united above to the dorsal portion of 

 the integument. 



