EXTERNAL CHAJRACTERS 105 



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 

 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 backwards 

 along the dorsal surface of the body : a similar 

 groove runs along the left side. 



Pass a seeker into the genital aperture, and backwards 

 clong 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 away 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 pulmonary chamber. 



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



below and to the right of the respiratory 



aperture. From it a spout-like groove runs 



forwards to the edge of the collar. 



Glean the anal opening and groove, and pass a seeker 



into the anus and back along the rectum. 



