ig 4 



THE YOUNG NATURALIST. 



comes the power, for there are no muscles to pull it into position ? 

 This is accomplished by the aid of the caudal forceps, with which 

 these insects are so formidably armed, for they are employed by the 

 creature to double over and tuck the wings under the elytra. 



The Diptera possess but two anterior membranous wings, the 

 posterior taking the form of two slender, clubbed organs, termed 

 halteres, or poisers (halter, a plummet), which vibrate sympathetically 

 with the wings. Owing, therefore, to the almost obsolete nature of 

 the second pair of wings, we must be prepared to find the mesothorax 

 much enlarged, the remaining two, perforce, dwindling to minute and 

 indistinct segments. The fore-wings are frequently provided at their 

 inner margin, and near the base, with small membranous appendages, 

 called alula, or winglets, but we can only regard them as an extension 

 and modification of the wings to which they are attached. 



It will not be out of place to briefly consider the probable part 

 taken by the true wings and their metathoracic representatives in the 

 production of the well-known and equally disagreeable buzz of the fly. 

 By having carefully compared the conflicting opinions of various 

 authors upon the subject, it appears to me that these and other organs 

 individually produce sounds independently of and in combination with 

 each other, the entire aggregation resulting in a continual buzz or 

 hum. De Geer was of the opinion that the sound is evolved by the 

 rubbing or friction of the roots of the wings against the sides of the 

 cavities forming their points of insertion into the thorax. That this 

 is one of the causes there is not much reason to doubt, though it is 

 probable, as I shall hereafter show, that the very conditions of the 

 experiment necessary to prove his theory, remove the possibility of 

 the sound being produced by any other means. Take a specimen of 

 Musca vomitoria, the common blue-bottle or meat-fly, and stretch its 

 wings out in opposite directions, holding them between the finger and 

 thumb of each hand. The buzzing continues until they are extended 

 so tightly as to prevent the slightest motion, when it is found to in- 

 stantly cease. Furthermore, if the wings be cut off close to the 

 base, the sound will continue until they have been plucked out com- 

 pletely. 



I have already expressed an opinion that the halteres and the alulae 

 play no important part in the production of this sound. Taking an 

 example from a species of Tabanus, it is found that the membranes of 

 the wing become widely separated in the alulae, though still united 

 round the edges, thus forming a species of hollow sounding board, in 

 form like unto a concavo-convex lens. Two drumsticks are supplied 



