BUSYCON. 133 



8. In structure the shell presents three layers. In a broken 

 shell notice : (a) the cuticle, worn away from the greater portion 

 of the shell; (6) the nacre, smooth and Hning the inner surface 

 of shell; (c) the middle layer. How can three layers be secreted 

 by the mantle? 



Draw two figures, one of a perfect and one of a broken shell. 



9. Compare the shell with the shells of other forms, such as 

 Polinices, Bulla, Haliotus, Crepidula, and Acm2ea. 



Soft Parts. — Examine an animal that has been removed from 

 its shell and killed while more or less expanded ^ and see in what 

 position it was placed in the shell. Compare the number of 

 whorls made by it to the number in the shell. Understand which 

 is right and which is left for the coiled part of the body. Wnich 

 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. 



* This can be accomplished by breaking the shell away with the blade 

 of a hatchet, and when enough of the shell has been removed, loosening the 

 muscle from the columella with the thumb, and then pulling and twisting 

 the animal out. When free from the shell place the animal in sea-water 

 to which has been added about one-tenth its volume of alcohol and a little 

 turpentine (about 10 c.c. of turpentine to each 100 c.c. of alcohol) and leave 

 for several hours. An animal treated in this way will usually die with its 

 proboscis extended. For the method we are indebted to Mr. Geo. M. 

 Gray, Curator at the Marine Biological Laboratory, Woods Hole, Mass. 



