DIPTEEA. 



79 



and forming a more or less obtuse angle (Fig. 56). The first portion 

 of the trunk, that which joins the head, is perfectly membraneous 

 and in the form of a funnel. We will call it the conical part and 

 show it separately (Fig. 57). The second portion terminates in a 



Fig. 56. Trunk of the Meat-fly. 



Fig. 57. Conical part of the trunk. 



Fig. 58. Ketractile proboscis 

 of Blue-bottle fly. 



thick mass, in part cartilaginous or scaly, and of a shiny brown 

 colour. Above the conical portion are two oblong antennae, with- 

 out joints, of chesnut colour, and furnished with hairs. 



On ceasing to press the thorax, the membraneous conical por- 

 tion may be seen to draw itself back within its sheath (Fig. 58). 

 The second portion is at the same time 

 drawn into the cavity, but it raises itself 

 by forming a more and more acute angle, 

 so that when it reaches the opening of the 

 cell its length is equal to that of the cell, 

 which is quite large enough to receive 

 the second portion. The thick part is 

 lengthened and flattened a little, and conceals the trunk. 



Let us cause the trunk to extend itself a second time, in order 

 to observe its end minutely. Here the opening is placed, which 

 may be looked upon as the mouth of the insect, and is provided 

 with two large thick lips (Fig. 59). These lips form a disk, 

 perpendicular to the axis of the trunk ; the disc is oval, and is 

 divided into two equal and similar parts by a slit. The lips 

 have each a considerable number of parallel 

 channels situated perpendicularly to the slit. 

 These channels are formed by a succession of 

 vessels placed near each other. On pressing 

 the trunk we see that these vessels are distended 

 by a liquid. Eeaumur, from whom we borrow 

 these details, discovered a few of the uses to which this trunk 



Fig. 59. -Extremity on the 

 proboscis of a fly. 



