ME THODS OF S TUDY. 211 



extrusion of a part of the seventh and the eighth segments 

 from the cloaca. 



The details of the structure and relations of the segments 

 forming the cloaca of the male and the ovipositor in the female 

 and their appendages will be given in the description of the 

 external generative organs. 



APPENDIX TO CHAPTER V. 



METHODS OF STUDY. 



In the study of the exo-skeleton of an insect the simple micro- 

 scope is far more useful than the compound instrument, except 

 when the more minute details are in question, and then low 

 powers and a good binocular are most desirable. Except when 

 the parts can be mounted in balsam without pressure, direct 

 light should be used in preference to transmitted. 



The slides which are usually prepared and sold as examples 

 of insect anatomy are in general useless, as the parts are 

 crushed and overlap each other. 



The microscope which I prefer for use in dissection is 

 Huxley's model, as made for the Normal School at South 

 Kensington, with Zeiss' triplets. These leave nothing to be 

 desired. 



For the study of the general structure of the exo-skeleton a 

 number of artificial exuvia should be prepared. I effect this 

 in the following manner : I steep the insects in a five per 

 cent, aqueous solution of caustic soda for a week, or until 

 all the soft parts are dissolved, and then wash them with dis- 

 tilled water. The washing must be very thorough, as even a 

 trace of the caustic soda adhering to the insects' skeletons will 

 destroy them afterwards, or, by forming crystals of soda salts, 

 render the specimens worthless for future use. 



In warm weather I find equal parts of alcohol and a ten per 

 cent, caustic soda solution preferable for steeping the specimens, 

 but they need a longer immersion. When the soft parts are 



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