— 2 9 — 



amined more than counterbalances the unpleasant part of 

 the preparation of the specimen. 



PRESERVATION OF SPECIMENS. 



Specimens that are to be used for the study of internal 

 anatomy should be preserved in an aqueous solution of chlo- 

 ral hydrate ; this is made by dissolving one part by weight 

 of chloral hydrate in twenty parts of water. This liquid 

 preserves the organs and at the same time leaves them flexi- 

 ble. After the specimens have been in the solution for one 

 day, a short, longitudinal slit must be made through the wall 

 of the abdomen, so as to allow the solution to enter the peri- 

 visceral cavity ; otherwise the viscera will decay. The de- 

 lay of one da}- before making the slit in the body is impor- 

 tant ; if the slit is made too soon, the muscles will contract 

 in such a way as to distort the specimen and render it worth- 

 less. One-half of the specimens should be slit on the dorsi- 

 meson, the others, on the ventrimeson ; for if the specimens 

 are all cut in the same manner, it will be impracticable to 

 study certain organs. 



If a very careful study is to be made of the external anat- 

 omy of this larva, one or more spacimens should be left for 

 several days in a warm place, in the chloral hydrate solution, 

 without being cut. The parts bathed by the solution will 

 be well-preserved ; the viscera will decay ; and the gases of 

 decomposition will so distend the body that the different 

 sclerites will be spread apart. 



EXTERNAL CHARACTERISTICS. 



In order to understand the internal anatomy of this insect 

 it is necessary to know the more general features of its ex- 

 ternal anatomy. We will not stop to trace out the homol- 

 ogies of the different sclerites which enter into the compo- 

 sition of the body wall, but will merely examine the more 

 important external structures. 



