THE HOUSE-FLY. • 631 



edges becomes either pentagonal or even square. It consists of 

 a conical transparent body, called the cone, which is set in a layer 

 of dark red pigment. If a fly be crushed, this pigment escapes, 

 and looks just like blood. Then follows the 'rod,' a delicate 

 fibre which connects the cone with nerve-centres in the head. 



The whole of this structure has been thoroughly worked out 

 by Mr. B. T. Lowne in his valuable monograph on ' The 

 Anatomy and Physiology of the Blow-Fly,' a work which every 

 entomologist ought to possess, as the information which it 

 gives does not merely relate to the particular insect of which 

 the author treats, but explains the structure of various other 

 insects. Having myself dissected great numbers of Blow-Flies, 

 I am qualified to express an opinion on the subject, and to 

 appreciate the careful pains and labour that the author has 

 bestowed upon his investigations. 



At Fig. b is given an outline drawing of the foot, with its 

 two pads. The structure of this member has already been 

 described, so that we need not refer to it again. At Fig. e is 

 given a side view of the proboscis, showing its right lobe. 

 This instrument forms a most beautiful object in the micro- 

 scope. The two lobes are then seen to be traversed by a 

 number of air-tubes of a rather peculiar structure, all radiating 

 from two principal tubes, one to each lobe. 



Generally the air-tubes or tracheae of insects are kept in 

 shape by a spiral thread between the two layers of which 

 they are composed, but in the air-tubes of the proboscis the 

 place of the spiral thread is taken by a number of incomplete 

 rings, called false tracheae. These incomplete rings look some- 

 thing like the ancient torque, or, to speak more familiarly, like 

 a horse-shoe. The open part of each ring is downward, and 

 the result of this structure is that they form a sort of strainer 

 through which the liquid portions of their food are passed. 

 The shape of this curious organ is greatly varied, and although 

 the proboscis of every Fly agrees in the principles of its 

 construction, there are not any two species which have it 

 exactly alike. 



At Fig. 1 of Woodcut LXXV. is shown the common House- 

 Fly {Musca domestica), slightly magnified. In all the insects 

 belonging to this genus, the trausformation is conducted in 



