5H 



of waste products, and the only parts of the gills 

 performing any really important duty in respiration are 

 the branchial expansions of the principal filaments. 



ALIMENTARY CAXAL AXD DIGESTIVE GLAND. 



The Alimentary Canal of Pecten is comparatively 

 simple, and there are no complicated convolutions in the 

 visceral mass as in Cardium. The total length is about 

 twice that of the longest antero-posterior diameter of 

 the body. 



In order to examine the alimentary canal, it is 

 necessary to remove the mantle and gills from the right 

 side, and it will be easier if the specimen has been left for 

 a day or so in 5 per cent, aqueous solution of formol. 



The course of the alimentary canal in the visceral 

 mass can be best made out by shaving off slices parallel 

 to the surface. Sections will also best show the shape 

 and position of the stomach. 



The mouth (fig. 39, M .) is situated between the lips 

 which are conspicuous dorsal to the foot (fig. 39, L-p. u., 

 Li). I.). It is hidden completely by them, and food 

 particles pass into it by being carried forward at each 

 side of the visceral mass and foot between the labial palps. 



The Labial Palps (tigs. 1 and 39, L. p. e. and L. p. i.) 

 consist of an inner and an outer broad flap on each side of 

 the visceral mass at the points where the gill lamellae 

 terminate dorsally. The outer is a continuation of the 

 upper lip, and the inner palp of the lower lip. They are 

 pigmented yellow-brown, but are very thin and somewhat 

 transparent. The inner palp is rectangular in shape, and 

 is attached to the visceral mass along the inner long edge 

 and the sliort ventral edge. The attachment is, however, 

 confined to these two edges, and the whole area is 



