101 BRITISH APHIDES. 



In such cases a weak solution of common salt, or very 

 dilute glycerine, or sugar and water, or albumen and 

 water, all of which should nearly approach the density 

 of the juices of the insect, will be found a considerable 

 help. 



Some Aphides are so large, so full of liquid, and so 

 charged with oil-globules, that some treatment is 

 necessary to reduce their bulk, and to allow of a 

 sufficiently thin stratum of balsam for mountiug. 



In such cases the Aphides may be placed in spirits 

 of turpentine, and just raised to the boiling-point in 

 a small test-tube. After soaking in the turpentine 

 for a few hours, all the oil-globules will be removed, 

 and the insect, by this treatment, will have become 

 very transparent, and the aqueous parts will not then 

 chill the balsam. 



To prepare Aphides for dissection, liquids may be 

 divided into those used for hardening the tissues and 

 those employed for colouring the same. For harden- 

 ing, a digestion for several hours in weak alcohol will 

 be of advantage. The alcohol must not be too strong, 

 or the albuminous portions will be coagulated and 

 become too opaque. 



Weak acetic acid will render some portions tough, 

 and the same action is also well effected by a weak 

 solution of phosphoric or of nitric acid. 



The action of ordinary ether upon Aphides is not 

 well understood. Their bodies are speedily destroyed 

 by plunging them into the liquid. At the same time 

 a considerable stream of air-bubbles contained in the 

 tracheaa is expelled, and of such a volume as would 

 lead to the supposition that much of this air must be 

 in some state of solution in the body- juices. 



The reaction of weak potash has been before noted. 

 As a rule, the germinal matter resists its action for a 

 considerable time. Simultaneously this reagent usually 

 stains it of a bright gamboge yellow. In some genera 

 (notably Lachnus and Dryobius) potash deepens very 

 markedly tho violet dyo natural to these Aphides. 



