Objects for the Microscope. 83 



ANTENNA OF SILKWORM MOTH. 



These will form an example of the variation of the An- 

 tennae in the sexes, those of the male Moth being pecti- 

 nated throughout equally, while those of the female have 

 shorter branches, and alternately one long and one short. 



To prepare the antennaB of Bees, Wasps, and Flies, for 

 these observations, it is necessary to soak them in chlorate 

 of potash, with a few drops of hydrochloric acid, until they 

 are colourless ; then dry them and mount in balsam. . 



SPIRACLES AND TRACHEAE. 

 SPIRACLES OF DYTISCDS. 



The Dytiscus is a large Water-beetle, very common in 

 ditches and ponds, belonging to the pentamerous Coleop- 

 tera. It passes its first stage of existence wholly in the 

 water as a most voracious larva, with long narrow body 

 and strong head, armed with mandibles, breathing by the 

 anus, and rising frequently to the surface, when it hangs 

 head downwards and the body curved like an S. When 

 full-grown as larva it buries itself in the earth, changes to 

 a pupa, and afterwards to the perfect insect. It is from 

 the Beetle that these spiracles or breathing organs are 

 taken. 



Few objects are more beautiful than those prepared from 

 the respiratory apparatus of insects. The blood of insects 

 is aerated, not by its passing through particular organs, as 

 the lungs in some land animals, or the gills offish ; but the 

 air is circulated in every part of their body by means of 

 delicate spiral vessels, called tracheae, or air-tubes, which 

 ramify into the minutest organs. As you observe these 

 spiracles, look also at these slides, which are very commonly 

 found in all collections. 



TRACHEA OF DTTISCUS. 



You see they greatly resemble the spiral vessels of plants ; 

 within the outer membrane an elastic fibre winds round and 



