Fresh-water Mussel. 59 



before it disengages itself from the mass they make up. Of these, 

 the one directly continuous with the stomach, is placed between 

 the other two, and two raised ridges are visible upon its inner 

 surface — one, the larger of the two, upon its neural, the other, the 

 more delicate, upon its haemal aspect. With this first loop, the 

 one placed most externally is continuous, and is seen bending 

 sharply back from, and closely round upon it along the posterior 

 free margin of the foot. Upon its surface there is no longitudinal 

 ridge developed, but a raphe with jdica running from it at right 

 angles to the long axis of the intestine. It is in close relation 

 with the muscular strata of the ' foot.' In ends in the third loop, 

 which at its beginning passes over the first so as to become quite 

 superficial in the middle of the right side of the visceral mass ; 

 and then takes a horizontal course, as seen in this preparation, 

 to the haemal border of the animaFs body, at a deeper level parallel 

 to and immediately posteriorly to the portion of intestine imme- 

 diately continuous with the pyloric end of the stomach. Where it 

 reaches this deeper level, a raised ridge is developed upon it, which 

 commences with a club-shaped end, and is prolonged on the neural 

 wall of the intestine as far as the anus. After thus completing its 

 third coil, by reaching the haemal edge of the visceral mass, the 

 intestine emerges from it, and turns at a right angle to its previous 

 direction to pass, as in the great majority of Lamellibranchiata, 

 through the heart, the cut edge of the ventricle of which is seen to 

 the left of the intestine. The pericardial space appears, in section, 

 as a triangular cavity, bounded by the heart and intestine to the 

 left, the retractor pedis posterior below, and the organ of Bojanus 

 to the right. The two cavities or sacs of which this organ is made 

 up, are well seen in section; though the walls of the superiorly 

 placed and non-glandular sac are more nearly in apposition than in 

 nature. The lamellate glandular sac is seen prolonging itself 

 around the tendon of the posterior retractor, and along the anterior 

 and inferior surface of the posterior adductor. Posteriorly again 

 to the posterior adductor, we see the attachment of the gill of the 

 left side to the mantle at a point corresponding to the junction 

 of the fimbriate with the non-fimbriate portion of the mantle. 

 The preparation is suspended by the apex of the muscular * foot ;' 

 by the protrusion and implantation of which into the soft bottoms of 

 the ponds and streams in which these creatures live, they can move 



