32 



and the ease with which the internal organs can be examined 

 more than counterbalances the unpleasant part of the prepara- 

 tion of specimens. 



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 pre- 

 serves the organs and at the same time leaves them flexible. 

 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 perivisceral 

 cavity ; otherwise the viscera will decay. The delay of one 

 day before making the slit in the body is important ; if the 

 slit is made too soon, the muscles will contract in such a way 

 as to distort the specimen and render it worthless. One-half 

 of the specimens should be slit on the back, the others, on 

 the ventral side ; 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 specimens 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 de- 

 composition will so distend the body that the different scle- 

 rites 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- 



