50 ON THE ANATOMY OF THE FLY. 



upon the fissure, without impairing the action of the sucker or altering 

 the position of its edge. These bands are dissolved by liquor potassse, 

 they exhibit a dark outline ; do not swell up when treated with acetic acid 

 and are elastic. They are developed from spindle-shaped nucleated cellsj 

 which may be found in great numbers in the lobes of the proboscis of the 

 immature fly. 



There is no better method of examining the proboscis, in 

 order to obtain a general idea of its structure and functions, than 

 by observing that of a living fly whilst in action. This may be 

 conveniently done by enclosing the insect in a live-box, with a 

 few spots of syrup on the thin glass cover, and illuminating it 

 from above. This method was first suggested by the late 

 Richard Beck. Another very good way of examining the entire 

 organ, is to take a recently killed fly ; exsert the proboscis by 

 pressing on the thorax, and tie its base to keep it distended. 

 It may then be examined dry, or mounted in glycerine, in which 

 it becomes a very beautiful object, when it has soaked in that 

 medium a sufficient time to become transparent, especially if 

 illuminated by a black spot lens, as recommended by Mr. 

 Suffolk. This method is subject to the grave objection that 

 specimens so obtained are unnaturally tumid, and assume an 

 appearance quite unlike that natural to the organ. Sections of 

 the proboscis made with a lancet, or the entire organ cut off 

 and mounted in glycerine, are the most instructive specimens, 

 and are the only means of making out the minute anatomy of 

 the part. Those required to show the distribution of nerves 

 should first be hardened in spirit, or chromic acid. Numerous 

 recent sections should be examined as well as mounted specimens. 

 Mr. Topping's well-known and beautiful preparation only 

 exhibits the chitiiious parts, and the rneiitum is cut away in 

 order that the lobes may lie flat : although most useful as a 

 means of examining the structure of the false tracheal channels 

 and the teeth, the relations of the parts are so altered by 

 pressure, that some cannot be made out at all. All the hard 

 parts may be seen in situ by treating the whole head, with the 

 extended proboscis, in the manner already recommended fo* 

 examining the integument of the head ; but it is very difficult 



