The Microscope and Biology. By W. Wesche'. 421 



good preparations can be secured by careful watching, taking the 

 insect out of the solution immediately the chitin is thoroughly 

 softened and will not crack with pressure. They are beautiful 

 symmetrical objects, and can be easily traced to their openings, 

 the stigmata, particularly in the longer ovipositors, where the 

 membrane is transparent. The stigma has a minute apodeme or 

 lever to control its aperture ; this lever in the flies undergoes great 

 changes in appearance, so that it is occasionally possible to find 

 the place of an insect in the classification by a sight of this 

 part alone. 



4. Eggs will often be met with in various stages of development. 

 In Pcriplaneta the capsule that contains them can be seen, but 

 certainly not recognised, as it appears as a mass of folded chitin. 



When eggs are present in the flies, the abdomen is full of them ; 

 the receptacula seminis in some species are egg-shaped, but are 

 usually only three in number and can thus be distinguished, but 

 the beginner is very likely to take them for eggs. 



5. Larvae when present will always show, as their jaws will 



Fig. 115. — Jaws of the larva of Lucilia sericata Mg. These larvse infest the 

 fleeces of sheep. Most of the larvae in the Muscidge have the trophi of this type. 



not dissolve. There are many species of the large Muscid family 

 that are viviparous, and a slide with the jaws of the larvae showing 

 in the abdomen will absolutely settle this point in the life-history. 

 I have preparations of Oliviera lateralis F., Plagia trepida Mg. and 

 Phorocera serriventris End., showing these jaws. In the latter 

 case a problem at once presents itself. The female has a remarkable 

 ovipositor, of which the principal part is a curved hook turned in 

 under the abdomen. (Not at all resembling in arrangement this 

 part as found in the Pipunculidae.) The question arises, to what use 

 does an insect put an ovipositor when that insect does not lay eggs ? 

 One day a field naturalist will notice this fly boring holes in 

 something that will contain food, or abraiding with the under 

 surface of the abdomen some leaf or plant and depositing larvae. 

 The edges of the plates on the under side of the abdomen are 

 spined (hence Eondani's name). This elaboration exists for some 

 very specific purpose, but here the limitations of what I may call 

 the " arm-chair method " come in, and we must wait for the field 

 naturalist to solve the problem. Even here the Microscope affords 

 a clue that may suggest a solution. The " scent pits " on the 



