

EXTERNAL CHARACTERS. 119 



b. The foot is a large flattened muscular expansion of 



the ventral wall of the body. It is of an elon- 

 gated oval shape, commencing in front with a 

 rounded anterior border immediately below and 

 behind the head, and narrowing behind to a long 

 pointed extremity. A median longitudinal groove 

 runs along its ventral surface. 



Watch the under surface of the foot as a snail creeps along 

 a sheet of glass, and note the waves that pass from behind for- 

 wards along the muscles. 



c. The collar is a thickened fleshy rim surrounding 



the mouth of the shell, and separated by a deep 

 groove from the body which it encircles. It is 

 thicker at the sides than in front or behind, and 

 is especially thick on the right side in the angle 

 of the mouth of the shell. 



d. The external apertures. 



i. The mouth is a small aperture on the ventral 

 surface of the anterior end of the head. It 

 is bordered at the sides by two prominent 

 lateral lips, and is separated from the foot by 

 a less conspicuous inferior lip. 



Pass a seeker into the mouth, and then upwards and back- 

 wards into the cavity of the buccal mass. 



ii. The genital aperture is on the right side of the 

 head, behind and below the larger tentacle, 

 and immediately behind the' posterior edge of 

 the right Up. From it a groove runs back- 

 wards along the dorsal surface of the body : 

 a similar groove runs along the left side. 



Pass a seeker into the genital aperture, and backwards 

 along the genital passage. 



iii. The respiratory or pulmonary aperture. On 



the right side of the Collar at its widest part 

 is a deep notch, at the dorsal end of which 



