EXTERNAL CHAEACTERS. Ill 



extremity. A median longitudinal groove runs 

 along its ventral surface. 



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 sheU. 



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 Up. 

 Pass a seeker into the mouth, and then upwards and 

 backwards 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 lip. 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 backivards 

 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 

 is a large round hole, the respiratory aperture, 

 leading into the pulmonary chamber. 



Wash aivay the mucus from the collar on the right side ; 

 clean the notch in the collar, and pass a seeker through the 

 respiratory aperture into the pulmonari/ chamber. 



iv. The anus is a smaller slit-like hole, immediately 

 below and to the right of the respiratory 

 aperture. Prom it a spout-like groove runs 

 forwards to the edge of the collar. 



