MODE OF DISSECTING INSECTS. 293 



removed, and the insect by this treatment will have become trans- 

 parent, 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 coloring 

 the same. For hardening, 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 or din ary ether upon Aphides is not well under- 

 stood. Their bodies are speedily destroyed by plunging them into the 

 liquid. At the same time a considerable stream of air-bubbles con- 

 tained in the tracheae 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 a bright gamboge yel- 

 low. In some genera (notably Lachuus and Dryobius) potash deepens 

 very markedly the violet dye natural to these Aphides. In other 

 cases I have found potash to evoke the violet shade from specimens 

 otherwise colorless. This dye is fugitive, and if discharged by an 

 acid cannot be again recovered by the action of an alkali. Soda 

 and ammonia also bring out this color. 



"Advantage may be taken of the fact that there is a certain order 

 in which the tissues resist the intrusion of a foreign matter such as a 

 dye. Thus the germinal and most vitally endowed organs reject 

 dying by carmine, logwood, and such coal-colors as magenta; whilst 

 the portions in process of exfoliation and decay absorb it the 

 most readily. For such purposes, weak alcohol may be made 

 slightly alkaline by ammonia, and tinged with a little carmine or 

 cochineal solution. Dilute chromic acid both tinges the tissues 

 yellow and renders them tough. Solutions of osmic acid also may 

 be used to advantage, and, in short, the usual reagents employed for 

 conducting minute anatomy may be taken with due circumspection 

 and tenderness. 



"For labelling specimens, paste will be found much more adherent 

 than gum. The former may be preserved for some months in a 

 well-closed bottle, if a little aqueous solution of corrosive sublimate 

 be stirred into it." ("Monog. British Aphides," iv. (1883) pp. 193-5.) 



