THE MICROSCOPE IN ZOOLOGY. 177 



a curious modification of tracheal structure, which is 

 thought to serve the function of suction (Plate XVII, 

 Fig. 134). The tongue of the bee is also an interesting 

 object. In the Diptera the labrum, maxillse, mandibles, 

 etc., are converted into delicate lancets, termed setse, and 

 are used to puncture the epidermis of animals or plants, 

 from which the juices may be drawn by the proboscis. 

 In the Lepidoptera the labrum and mandibles are reduced 

 to minute plates, while the maxillae are greatly elongated, 

 and are united to form the haustellum, or true proboscis, 

 which contains a tube for suction. 



Feet. Tbese organs vary with the habits of life in dif- 

 ferent species. The limb consists of five divisions : the 

 coxa or hip, the trochanter, the femur or thigh, the tibia 

 or shank, and the tarsus or foot. This last has usually 

 five joints, but sometimes less. The Cdeoytera are subdi- 

 vided into groups, according as the tarsus consists of five, 

 four, or three segments. The last joint is furnished with 

 hooks or claws, and in the fly, etc., the foot is also 

 furnished with membranous expansions, called pulvilli. 

 These latter have numerous hairs, each of which has a 

 minute disk at its extremity. By these, probably by the 

 secretion of a viscid material, the insect is enabled to 

 walk on glass, etc., in opposition to gravity (Plate XVII, 

 Fig. 135). In the Dytiscus, tne inner side of the leg is 

 furnished with disks or suckers of considerable size. 

 They may be mounted as opaque objects. Stings and 

 Oi'i positors also present a great variety of structure, and 

 may be best mounted in balsam. 



The alimentary canal in insects presents many diversi- 

 ties. As in higher animals, it is shorter in flesh-eaters 

 than in feeders on vegetables. It consists of: 1. The 

 oesophagus, which is sometimes dilated to form a crop. 



2. The muscular stomach, or gizzard, whose lining mem- 

 brane is covered with plates, or teeth, for trituration. 



3. A cylindrical true stomach, in which digestion takes 



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