PRESERVING HEMIPTERA. 281 



The soft-bodied species of Aphis or plant-lice should be 

 preserved in alcohol, glycerine, or Canada 

 balsam. They should be carefully watched 

 for their parasites, and can be easily kept 

 in slender glass vials, through which they 

 can be observed. 



All the bugs should be pinned through 

 the distinct triangular scutellum, situated 

 in the middle at the base of the wings FlG 373. Method of 

 (Fig. 273). The small, hard species of pinning a bug. 

 leaf-hoppers should be pinned through the right wing- 

 cover. Various quadrupeds should be carefully examined 

 for lice, which may be preserved in alcohol, or mounted on 

 slides for the microscope. 



Examining Live Aphides. Mr. H. J. Slack says that when we want 

 live aphides to examine under the microscope in a vigorous condition, 

 we must handle them with extreme gentleness, or their soft and deli- 

 cate bodies will be injured and the creature killed. Their slightness 

 of structure is, however, accompanied with great endurance of con- 

 ditions that would be quickly fatal to many stouter organisms. Most 

 insects would be rapidly killed by immersion in paraffine oil ; but 

 young and vigorous aphides will often live lor some time, and occa- 

 sionally for hours, in this fluid, such as is burnt in lamps. If two or 

 three of the insects are very carefully placed in a little cork cell,* 

 filled with paraffine oil, and covered with thin glass, they are in a 

 handy condition for examination. The result of numerous experi- 

 ments made with the best American petroleum oil, commonly called 

 crystal oil in the lamp shops, is that the survivals are very uncertain, 

 but sufficiently frequent for the process to be well worth trying. 

 They keep pretty quiet in the fluid, and it enables higher powers to 

 be used with convenience. A A inch objective, magnifying about 100 

 linear, with a full -sized instrument, is very handy. The illumination 

 should be varied; but one of the best ways is to use both an achro 

 matic condenser and a lieberkuhn, or little silver reflector, at the end 

 of the objective. The largest hole and central stop of the condenser 

 will give a fine dark-ground illumination. When used in combination 

 with the lieberkuhn, it lights up the inside of the object, while the 

 less transparent parts receive reflected rays from the silver surface. 

 The student will find a great many cases in which this mode of treat- 

 ing a refractive and reflective object produces the best results. The 

 eyes of the Aphis, seen in this way, are like half mulberries, and the 

 little eye projecting from the corner of the larger group is well dis- 



* A vial-cork | inch in diameter cut across so as to make a disk 

 T \ inch thick, with an oblong hole in the centre, and gummed on a 

 slide. The gum is not dissolved by paraffine oil. 



