154 MOLLUSC A 



6. The fold of tissue behind each eye. These have been 

 called the olfactory organs, but there is no experimental evi- 

 dence of function. 



7. The small pore in front of the eye, the aquiferous pore. 

 With what does this communicate? 



8. The attachment of the head and the extent of the man- 

 tle opening around the neck. 



9. The funnel protruding from beneath the mantle on the 

 ventral surface. Notice the position and character of its 

 opening. 



10. The median dorsal projection of the mantle. 



11. The tail fin, its position and shape. What is its func- 

 tion? 



Draw the animal as seen from the ventral side. 

 Carefully open a specimen by cutting through the mantle 

 a little to one side of the midventral line. 

 Notice : 



1. The thickness and character of the mantle and its rela- 

 tion to the rest of the body. Why does it need to be so 

 muscular? 



2. The arrangement of the funnel. Why does it have a 

 thin posterior edge? How is it held in position against the 

 mantle? Does it have a valve? Is the funnel movable in 

 the living animal? Is there any provision for movement? 



3. The free edge of the mantle and its relation to the folds 

 beneath the eyes. Do you understand how the water gets 

 into and out of the mantle cavity? 



4. The large retractor muscles of the funnel. How many 

 are there? How can the funnel be pointed in different direc- 

 tions? What need is there for such a provision? 



5. The retractor rnuscles of the head. How many are 

 there? Are they used in swimming in any way? 



6. The rectum, opening near the base of the funnel be- 

 tween two small lateral flaps of tissue. 



7. The ink bag, dorsal to the rectum and opening into it 

 near the anus. 



