THE GRASSHOPPER 29 



the inside of this on each side of the spiracle until it is almost 

 transparent. Mount it as before with the outside up and 

 view it with the low power objective. Find a hard circular 

 ridge of chitin inside of which is a thin membrane with an 

 elongated opening in the center, sometimes open but gen- 

 erally closed. The elasticity of this inner membrane allows 

 the animal to breathe. Draw spiracle. 



Metamorphosis of the Grasshopper. — The eggs of the 

 Melanoplus differentialis are deposited in the fall and remain 

 in the ground during the winter. In the spring the larvae 

 emerge from the openings in the ground scarcely larger 

 than the eggs from which they came. They eat ravenously 

 and as they grow the membranous covering, at first thin 

 and elastic, becomes harder by the deposit of chitinous 

 matter, until the body cannot expand as it grows. The 

 animal then seeks a protected place, the hard shell is burst 

 behind the prothorax, and the animal crawls out of its old, 

 dry, hard skin and begins anew with a soft membrane. 

 After a short period of growth and rapid eating the shell 

 becomes hard again, the animal, considerably larger now, 

 bursts its shell and emerges as before. At about the third 

 molt the wings appear as very small projections from the 

 terga of the mesothorax and metathorax and at about the 

 sixth molt the now fullgrown animal is able to fly. 



Get a number of grasshoppers representing the different 

 stages of growth and note the differences in the wings and 

 posterior divisions of the abdomen in three or four stages 

 of the same species. Do you find differences in any other 

 parts of the body? 



Make drawings of the left side of three stages showing 

 the differences in form (X2). 



