68 Objects for the Microscope. 



these are ; the first and second bristly, the third is very 

 long, and the last three very short. It is important to 

 observe these things, as the shape of one joint in the an- 

 tennse will determine the species. In this very case, if we 

 were examining the large and true Tabanus bovinus, we 

 should see a very different third joint. 



Next let us examine the mouth. 



That long and broad membrane is called the labium. 

 Those lines at the inner edge of the two lobes are spiral 

 muscular fibre, which enable it to lap or draw up the fluid 

 it feeds on ; and those lancets are instead of jaws, or rather 

 are modifications of the mandibles and maxillse, which are 

 the inner and outer jaws of insects. These lancets pierce 

 the skin, and the labium sucks the blood of the horse. If 

 the slide has the head of Tabanus bovinus, and not the com- 

 mon Tabanus pluviatilis, also called Hsemotopota, or " blood- 

 drinking," the head will be armed with a strong pair of 

 mandibles besides the lancets. The larvae of these flies 

 live in the earth long grey footless .grubs, feeding on 

 decayed vegetables. 



PROBOSCIS OF GNAT. 



Here is another of our little tormentors, and a female 

 Diptera also ; for the male Gnat dances gaily in the sun- 

 shine with his beautiful plumed head, and has not by any 

 means so well-developed a mouth. He does not suck blood, 

 and probably sips a little nectar from flowers or the dew 

 upon the leaves in the short time he has to live : the busi- 

 ness of his life is to choose a mate and die. The female 

 Gnat lives longer, and is very bloodthirsty. Here observe 

 a long fleshy lip, or labium, which is the sheath containing 

 two mandibles, two maxillae, one labium, one ligula or 

 tongue. They may not all be visible on the slide, as some 

 may remain inside the sheath, and some may be broken off, 

 they are so very delicate ; but if perfect it would show all 

 these. The mandibles are finely toothed like a saw,- but 

 you require a quarter-inch glass to see this well. The 

 ligula is shaped like a spear-head. The stiff horny labium is 

 pointed like a needle. When the Gnat pierces the skin, 



