90 THE MICROSCOPIST. 



Heads, Mouths, &c. The manducatory apparatus of insects 

 is a subject of great interest to the entomologist. The divi- 

 sion of insects into Mandibulata and Haustellata are founded 

 thereon; the first having jaws, the latter a proboscis or suck- 

 ing instrument. Some of them require but little preparation, 

 and may be mounted as opaque objects; others, as the pro- 

 bosces and lancets of flies and bees, demand considerable skill 

 to display them to the best advantage. When thin and trans- 

 parent, they should be mounted in fluid, but if thick and opaque, 

 in balsam. Before mounting in the latter way, they should be 

 dissected while soft, and laid out on a slide to dry. 



Parasitic Insects should be placed in spirit and water in 

 order to kill them. They may be mounted in fluid or balsam. 

 Some of the large kinds may be examined as opaque objects. 

 The term Epizoa has been applied to them because occurring 

 on the exterior, in contradistinction to those occurring within 

 animals, which are called Entozoa. Some of them are classed 

 with insects, as having six legs ; while others, having eight, are 

 called Acari, and are included in the class Arachnida. 



Some very minute insects, called Aphides, are abundant on 

 plants, the leaves, &c., of which they destroy. Others, called 

 Cynips, are the cause of the excrescences on the leaves, &c., 

 of trees, termed galls. The well-known oak-apple is produced 

 by the Cynips quercus, which is a most elegant object when 

 examined by reflected light. The same may also be said of 

 the insect from the gall of the rose. Gather the galls when 

 ripe, and place them in a box covered with gauze. In a few 

 days or weeks numbers of insects will escape from the gall, 

 and those exhibiting beautiful colors may be selected. 



Among the Acari, may be mentioned the cheese-mite, A. 

 domesticusj and the itch-insect, A. scabiei. To obtain the 

 latter, the operator must examine carefully th,e parts surround- 

 ing each pustule, and he will generally find in the early stage 



