THE AMPHINEURA 43 
from head to anus. The breadth of the foot is inversely’ pro- 
portional to the width of the lower edge of the mantle: it is broad 
in most of the Polyplacophora, but narrow in the Cryptoplacidae. 
Extending all round the foot, between it and the mantle on the 
ventral side, is the pallial groove, in which lie the gills. In the 
more primitive Chitons mucous thickenings extend into the groove, 
v 
ao 2 
9°72. v 
Cy | 
! fe 
Fic. 24. 
Transverse section of the lateral portion of the pallial teguments of Chiton. I, tegmentum ; 
II, articnlamentum ; III, pallial epithelium under the shell; IV, epithelium of the margin of 
the mantle; V, spicula; VI, cuticle of the mantle-margin; VlIa, periostracum; VII, megal- 
aesthetes ; VIII, micraesthetes. (After Blumrich.) fi 
reaching from the anus to its upper corner, or to the foot, or even 
to the inner wall of the mantle. 
II. ANATOMY. 
1. The Alimentary Canal extends from one extremity of the body 
to the other. The mouth leads into the buccal cavity, on the ventral 
wall of which opens the radular caecum. The radula is long and 
reaches nearly as far back as the stomach. ach radular row 
includes seventeen teeth of various shape (Figs. 2, A; 74, E). The 
three central teeth are simple: on each side of them is a large 
