316 ELEMENTARY BIOLOGY. [CHAP. 



to form the locomotor foot ; a large, yellowish, 

 somewhat ploughshare-shaped mass, whose apex 

 projects freely between the mantle-lobes. 



b. The gills or branchiae; two lamellar organs on each 

 side of the body, extending to its posterior end. 



c. The labial palps ; a pair of membranous folds on 

 each side, in front of the gills and immediately 

 below the protractor pedis muscle. Note the 

 structural similarity between them and the gills. 



B. The pallial-lobes, in relation to adjacent structures and 

 the exterior. The branchial chambers and siphons. 



Remove the animal completely from its shell, by detach- 

 ing the other mantle-lobe from the valve to which it is fixed 

 and cutting through the attachments of the muscles to the 

 same. 



Pin down under water (the pins should preferably be 

 thrust through the adductor muscles). Raise the pallial 

 lobe nearest you with forceps and remove it, cutting along 

 its line of confluence with the underlying organs and the 

 body wall. Examine carefully 



a. The infra-branchial chamber; bounded above and 

 externally by the pallial lobe, a c of Section A. 3 

 lie within it. 



Follow the cut edge of the mantle, working from 

 behind forwards. It courses along the dorsal 

 border of the external gill lamella, whence it passes 

 downwards and backwards to reach the labial 

 palps; it skirts these in a similar manner, and is 

 continued on beneath the anterior adductor 

 muscle. 



