INSECTS 105 



d. Examine the hinge, and note the tough ligament that held 

 the halves of the shell together. Which act required muscular 

 effort on the part of the animal, to close the shell, or to open it? 

 Can you find on the hinge the device by which the shell was 

 thrown open? If the projecting material at the hinge forms the 

 fulcrum, if the stretching of the ligament represents the work to 

 be done, and if the contraction of the muscles is the power, what 

 kind of a lever is the shell when the clam is trying to close it? 



If you were trying to pry the shell open, and the clam were 

 trying to keep it shut, to what other class of levers would the 

 shell belong? Where would the power be as regards the ful- 

 crum and the new resistance? To exert the greatest force, 

 ought the muscles to be attached near the hinge or near the 

 ventral edge of the shell? Where are they attached? Why? 



e. If you have a clam or oyster identify the cut ends of the 

 muscles, also the mantle, foot, and "siphons." 



/. Carefully examine a snail shell; sketch an outside view of 

 it. If possible, get some one to saw lengthwise through an 

 empty shell, from the tip to the widest part. Draw a section 

 of the shell. In what part did the animal live first? 



g. Describe the body and movements of a living snail. 



EXERCISE 97 

 INSECTS 



Materials. House fly and horsefly, spider, ant, May beetle; if 

 possible, a butterfly or a moth; also a spider's web, the larva of a May 

 beetle (" white grub"), and a cocoon of the cecropia moth. 



A convenient way to catch a butterfly or moth is to use a bag of 

 mosquito netting attached to a ring and pole; for the other insects use 

 a wide mouth bottle. Put this over the insect; then slip a piece of 

 cardboard between the mouth of the bottle and the table or wall on 

 which the insect had alighted. 



