112 ELEMENTARY BIOLOGY. [XL 



f. The cloacal chamber: pass a probe through the 

 dorsal siphon; it will enter a small chamber, 

 separated from the pallial chamber by a par- 

 tition which unites the hinder part of the two 

 inner gills (c. /8.). 



c. The contents of the pallial chamber. 



a. The foot: a large, yellowish, somewhat plough- 

 share-shaped mass, in the middle line ; its apex 

 directed forwards and ventrally, towards the 

 front of the cleft between the mantle-lobes. 



/3. The gills or branchice: two lamellar bodies on 

 each side of the foot, but reaching farther back 

 than it does: the outer gill on each side, at- 

 tached to the mantle-lobe; the inner, attached 

 to the foot in front, but farther back separated 

 by a cleft from it; and behind the foot, united 

 across the middle line with its fellow so as 

 to form a partition separating the cloacal from 

 the pallial chamber. 



7. The labial palps: a pair of small triangular 

 processes on each side, in front of the gills and 

 on the dorsal end of the anterior edge of the 

 foot. 



8. The mouth: each labial palp is continuous with 

 its fellow across the middle line, and between 

 the lip-like ridges thus formed, lies the wide 

 mouth-opening. 



d* The anterior and posterior adductor muscles: if 

 the reflected mantle-lobe be turned down again, 

 the oval divided ends of the adductor muscles can 

 be seen. They appear to perforate the mantle. 



