180 THE BIOLOGY OF THE ANIMAL 



specimens. In studying the internal structure of the 

 locust, the two specimens are to be used in the follow- 

 ing manner: With the first one, cut off the wings, cut 

 the body in two lengthwise with a very sharp scalpel, 

 then, insect in hand, study the features mentioned here- 

 after. After having done this, prepare the second speci- 

 men as follows: Remove the wings, fasten the insect, 

 ventral side downward, in the dissecting-dish containing 

 fifty per cent, alcohol, by putting pins through the last 

 abdominal segment and each of the hind-legs, turning 

 the latter outward. Then begin at the posterior end, 

 and with fine, sharp scissors cut the skin along each side 

 of the body above the spiracles, turning the skin forward 

 as it is loosened, thus unroofing the body. Be espe- 

 cially careful not to injure the heart, which lies just be- 

 low the skin. Then proceed to verify the facts learned 

 from the first specimen. 



a. The integument. — Of how many layers is it com- 

 posed ? Can you find both epidermis and cuti- 

 cle ? What differences in their thickness, text- 

 ure, flexibility, color, and arrangement on the 

 body? Does the integument bear any outgrowths 

 corresponding to the " hairs " found on the lob- 

 ster ? If so, do they correspond in general posi- 

 tion to those on the latter animal? Put a piece 

 of the integument into dilute hydrochloric acid. 

 Do you get the same results as you did with the 

 lobster's shell ? Does the integument of the in- 

 sect contain carbonate of lime ? 



5. The heart (lying just under the skin). — Position? 

 What is its relation to the ridge running down 

 the middle of the back? Shape? Structure? 



