MICROSCOPIC OBJECTS. 66 



Fig. 131. Hop- Aphis (Aphis humuli), x 20. Order Hemi- 

 ptera, Division Homoptera. 



The insects of this division of the order Hemiptera are 

 chiefly distinguished by having their beak growing from the 

 lower part of the head also by not having the elytra half 

 coriaceous and half membranous as in the Heteroptera, but 

 all of membranous consistency. The Hop-Aphis is one of the 

 most troublesome insects to farmers ; and if it were not for the 

 larva of the Coccinella and other insects living entirely upon 

 them, they would be more so. The sweet fluid which these 

 insects secrete, called honey-dew, is much liked by ants ; this 

 fluid exudes from the two tube-like processes called " paps/' 

 situated at the back. On the ants pressing these "paps" 

 gently, they are able to procure this fluid, of which they are 

 extremely fond. These insects are best mounted in acetic 

 acid, in a shallow cell, sealed with liquid india-rubber or 

 dissolved gutta percha. 



Fig. 132. Wing-case (Elytron) of Water-boatman (Notoiiecta 

 glauca), x 5. 



The elytron of this insect has been taken to illustrate the 

 partially membranous and coriaceous elytra of the division 

 Heteroptera of the order Hemiptera, as mentioned at fig. 130. 

 On referring to the drawing, the membranous may be distin- 

 guished from the coriaceous or leathery parts, the membranous 

 being nearly transparent, and the coriaceous having a more 

 opaque appearance. 



This, together with most of the transparent elytra of the 

 various insects, requires scarcely any preparation, simply 

 soaking in hot water, and drying under strong pressure, then 

 placing it in turpentine for a few minutes, and mounting in 

 balsam. 



