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HANDBOOK OF INVERTEBRATE ZOOLOGY. 



placed in a basin of water, and sliced vertically ,with a 

 ra/or at intervals of half or one-third of an inch. The 

 sections should then be preserved for study under alcohol 

 in a shallow dish or saucer. The more instructive sections 

 are : one through the posterior portion of the posterior 

 adductor muscle ; one through the space between the pos- 

 terior adductor and the heart; one through the heart; 

 one through the middle of the abdomen ; and one through 

 the anterior portion of the abdomen. 



I. A section through the posterior adductor muscle. 

 In this, as in all the other sections, two main chambers 

 or cavities are to be noticed. 



a. The mantle cavity (Fig. 146, d, A), which is widely 

 open below, and contains the gills (Fig. 146, e,f). 



b. Above this, notice the body 

 cavity, which in this section is 

 almost entirely filled by the ad- 

 ductor muscle (Fig. 146, g), the 

 rectum (Fig. 146, p), and con- 

 nective tissue. 



FIG. 146. Diagram of a vertical section 

 of the body of Unio purpurea in the region 

 of the posterior adductor muscle. (Drawn 

 from nature by W. K. Brooks. ) 



a, a. Mantle lobes. b. Glandular epi- 

 thelial layer of mantle, c. Dorsal lobes of 

 mantle. d. Cloacal chamber of mantle 

 cavity, e, e. Inner gills. /,/. Outer gills. 

 g. Posterior adductor muscle, li. Branchial 

 chamber, ft'. Dorsal portion of mantle 

 cavity, p. Rectum. 



FIG. 146. 



c. Above the intestine is what appears to be another 

 small cavity (Fig. 146, A'), but if the posterior end of the 

 section be examined, it will be found to be part of the 



