MICROSCOPIC OBJECTS. 69 



Fig. 137. Eye of Dragonfly (Libellula depressa), x 200. 



The eye of the Dragonfly is well adapted for the work 

 which it has to perform, which is to perceive quickly any 

 insect in its rapid flight through the air. On examining a 

 Dragonfly the eyes will be found to comprise nearly all the 

 head ; they are also extremely prominent. The structure of 

 the eye is the same as in other insects (see fig. 126 &c.) ; but 

 the lenses are rather larger than those of the Diptera, Lepido- 

 ptera, &c. 



After separating the eye, it must be macerated for a short 

 time in the diluted potassa, well washed, and dried under 

 pressure ; it may then be mounted dry, or in a shallow cell 

 with acetic acid, or any other good preservative fluid. 



Fig. 138. Meadow- blue Butterfly (Polyommatus Alexis), 

 natural size. Order Lepidoptera. 



This Butterfly has been taken to illustrate the order. The 

 chief difference between the Moths and the Butterflies lies in 

 the antennae of the former terminating in a point, those of 

 the latter in a clavate or club-shaped end. The position of 

 the scales on the wing-membrane is nearly the same in both 

 divisions of the order (see fig. 142). Both Moths and Butter- 

 flies furnish a large series of instructive objects. One of the 

 most characteristic structures of the order is the proboscis 

 (see fig. 141). Many of the eggs are also most beautiful 

 objects (see figs. 143, 144). The scales as situated in situ 

 on the wings are generally best when mounted in a dry opaque 

 cell. 



