22 ON THE ANATOMY OF THE FLY. 



The direction and length of the hairs upon the pad are so 

 adapted to the oblique direction in which the strain is put upon 

 them when the tarsus is straight, that the insect has a perfectly 

 secure hold ; this is immediately released as soon as the tarsus is 

 curved, which is effected by the long slender tendon already men- 

 tioned. In the small house-fly the pads themselves are capable of 

 being curved, for the tarsal tendon branches, and is inserted into 

 the distal extremity of each pad. 



The legs are developed from six pear-shaped corpuscles ad- 

 herent to the nerves andtracherc of the larva ; the changes these 

 undergo are seen in Plate VI., and are described in the second 

 part of this work. 



Section VI. The Digestive System. 



The viscera of the fly are remarkable for their symmetrical 

 arrangnnent, a fact well worthy of note, as it is at variance with 

 the usual disposition of the viscera of animals, although I 

 believe lateral symmetry will prove the rule amongst insects. 



The organs of the mouth are extremely modified so that they 

 form a complicated proboscis admirably adapted for the purpose 

 of collecting food by suction ; and, although all the parts homo- 

 logous to the six lancets of the gadflies so terrible in those 

 insects, are present, they are all more or less intimately united to 

 the sheath of the proboscis, so that they are quite incapable of 

 inflicting a wound, but form by their union a long tubular mouth. 

 The extremity of the organ bears a pair of large fleshy lobes, 

 which form an oval sucker when open, by which the insect 

 collects its food, either receiving the nutriment so collected at 

 once into the opening of the mouth, which is placed between the 

 lobes, or straining the fluid from the solid part of the material on 

 \rhich it is feeding by means of a set of channels ( false trachea: ), 



