MICROSCOPIC OBJECTS. 75 



Fig. 149. Sting of Hive- Bee (Apis mellifica), x 20. 



The sting may be considered as a modified form of ovi- 

 positor (see figs. 125, 130). It consists of a sheath, divided 

 on the underside through its entire length; from this slit 

 the setae, or lancets, are protruded at will ; these lancets are 

 furnished at the extremity with fine teeth ; the entire appa- 

 ratus is supplied with very strong muscles, and both the 

 sheath and the setae can be withdrawn or protruded from the 

 abdomen at pleasure. At the base of the sheath are two 

 poison- glands, which poison, by the action of the setae, is 

 deposited in the wound made by them. The chief use of the 

 sheath appears to be to protect the fine points of the setae, or 

 lancets, from injury. 



After separating the sting from the insect, it must be sof- 

 tened by placing it in the diluted potassa fusa for a few hours, 

 after which it must be well washed, and the lancets drawn 

 out from the sheath with the point of a fine needle; they 

 must then be placed in a natural position, dried under pres- 

 sure, and mounted in balsam. 



Fig. 150. A Small Fly (Thrips physapus), x 20. 

 Order Thysanoptera. 



This extremely small Fly, being only about -^ inch in 

 length, has been taken to illustrate the order. The chief 

 structural peculiarities are : "Wings four, alike, long, narrow, 

 membranous, neither folded nor reticulated, with long cilia ; 

 mouth with two setiform mandibles, two triangular palpige- 

 rous maxillae, and a palpigerous labium ; tarsi 2-jointed, 

 vesicular at tip." The Thrips may generally be found in the 

 flowers of the small Bindweed or Convolvulus (Convolvulus 

 arvensis] ; and in sultry summer weather scarcely a Convol- 

 vulus can be found without them. 



Most flies are not at all difficult to mount ; they must be 

 macerated in the liquid potassa, according to size, from three 

 or four hours to three or four days, then pressed gently be- 

 tween slips of glass, so as to force out the contents of the 

 abdomen &c., then replace the insect in the potassa for a 

 short time, well wash in warm water, dry under pressure, 

 soak in turpentine until transparent, and mount in balsam as 

 usual. 



