118 MOLLUSCA. 



side was applied to the columella? In determining the position 

 of organs, constantly keep the sides in mind. 



Before beginning the dissection, note the following parts: 



1. The visceral dome. The portion that extended into the 

 spire of the shell. 



2. The mantle, which is thin and closely applied to the visce- 

 ral dome, and raised to form a thickened collar that extends 

 entirely around the body along a line that corresponds to the 

 aperture of the shell. 



3. The siphon, which is a spout-like prolongation of the col- 

 lar. Into what portion of the shell does it fit ? 



4. The mantle chamber. This can be seen by raising the edge 

 of the collar of the mantle. 



5. The head, which forms an anterior prolongation. 



6. The tentacles, forming two triangular projections on the 

 head. 



7. The eyes, pigmented spots on the outer edges of the ten- 

 tacles. 



8. The proboscis, which, when extended, protrudes from 

 beneath the portion that bears the tentacles. What is its size, 

 shape, and general appearance? It may be retracted entirely 

 into the body. 



9. The mouth, at the end of the proboscis. The end of the 

 odontophore may frequently be seen protruding from the mouth. 



10. The foot. What is its position, consistency, color, and 

 shape? 



11. The opening of the pedal gland, on the sole of the foot. 

 Is the pedal gland well developed in both sexes? Do you know 

 its function? 



12. The operculum. Notice its position and attachment. 



13. If the specimen is a male, the large, somewhat flattened 

 and bent penis, a little to the right and posterior to the right ten- 

 tacle. 



A number of organs may be seen through the somewhat 

 transparent mantle. These are: 



14. The liver, which forms the first two whorls of the spire. 

 Notice its color. 



