PREPARATION OF INSECTS. 517 



tracheae, or air-tubes, which branch off from the larger 

 system in the body. The common Fly, if caught when 

 only a few hours old, shows this equally well. 



The breathing apparatus of insects affords many inte- 

 resting objects for the microscopic cabinet. 



Mr. Quekett recommends the following as a simple 

 method of obtaining a perfect system of tracheal tubes 

 from larvae : A small opening having been made in the 

 body, it is to be placed in strong acetic acid, which softens 

 or decomposes all the viscera : the trachea may then be 

 well washed with a syringe, and removed from the body, 

 by cutting away the connexions of the main trunks with 

 the spiracles, by means of fine -pointed scissors. In order 

 to mount them, they should be floated on to the glass-slide, 

 and laid out in the position best adapted for displaying 

 them. If they are to be mounted in Canada balsam, they 

 should be allowed to dry upon the slide, and should then 

 be treated in the usual way ; but their natural appearance 

 is best preserved by mounting in weak spirit and water, or 

 Goadby's solution, using a shallow cell, to prevent pres- 

 sure. The spiracles are easily dissected out with a fine 

 knife and pair of scissors : they should be mounted in 

 fluid, when their texture is soft, and in balsam, when the 

 integument is hard and horny. 1 



Another way of preparing insects, is to press them as 

 much as possible between two glass slides, without crush- 

 ing, and to fasten the slides together with india-rubber 

 bands or a fine string, so that the parts may dry in the 

 compressed state. When subsequently soaked in oil of 

 turpentine, and mounted in Canada balsam, they become 

 much more transparent and distinct. By prolonged 

 maceration in the turpentine, the whole of the pigment 

 may be removed, the structure is then seen more dis- 

 tinctly. When the organs are very hard and thick, they 

 may be first softened in boiling water, or a solution of 

 potash, before being pressed. 



TRANSFORMATION OF INSECTS. 



The metamorphoses of the insect race offer some of the 

 most curious and wonderful of nature's phenomena for 



(1) See Memoire sur les Objects qui peuvent etre conserves en Preparations Micro- 

 scopiques, Paris, 1856 , which contains a complete list of all objects of interest. 



