ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 467 



and the insect by this treatment will have become 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 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 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 

 tracheae is expelled, and of such a volume as would lead to the suppo- 

 sition 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. Simulta- 

 neously this reagent usually stains it a bright gamboge yellow. In 

 some genera (notably Sachuus and Dryohius) potash deepens very 

 markedly the violet dye natural to these Aphides. In other cases I 

 Jiave found potash to evoke the violet shade from specimens otherwise 

 colourless. 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 colour. 



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 dyeing by 

 carmine, logwood, and such coal-colours 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 with 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." 



Transmission, Preservation, and Mounting of Aphides.* — G. B. 

 Buckton gives the results of his experience as to the best mode of 

 transmitting living Aphides, and also the best method for killing and 

 preserving such-like insects for future examination. 



As to transmission, the chief thing to be guarded against is desic- 

 cation, and no plan seems to be so successful as their inclosure in 

 ordinary quills stopped by plugs of cork or pellets of beeswax. The 

 substance of the quill is sufficiently porous to prevent mildew on the 



* 'Monogiaph of the British Aphides,' iv. (1883) pp. 188-93. 



2 I 2 



