116 THE VITAL FUNCTIONS. 



like the blade of a knife. These instruments 

 are sometimes constructed so as to form, by their 

 union, a tube adapted for suction. In the flesh- 

 fly, the proboscis is folded like the letter Z, the 

 upper angle pointing to the breast, and the lower 

 one to the mouth. In other flies there is a single 

 fold only. 



Those insects of the order Hymenoptera, 

 which, like the bee, suck the honey of flowers, 

 have, together with regular jaws, a proboscis 

 formed by the prolongation of the lower lip, 

 which is folded so as to constitute a tube : this 

 tube is protected by the mandibles, and is pro- 

 jected forwards by being carried on a pedicle, 

 which can be folded back when the tube is not 

 in use. The mouths of the Acephalous 3Iollnsca 

 are merely sucking apertures, with folds like 

 lips, and without either jaws, tongue, or teeth, 

 but having often tentacula arising from their 

 margins. 



Among fishes, we meet with the family of 

 Cyclostomata, so called from their having a cir- 

 cular mouth, formed for suction. The margin 

 of this mouth is supported by a ring of cartilage, 

 and is furnished with appropriate muscles for 

 producing adhesion to the surfaces to which it is 

 applied ; the mechanism and mode of its attach- 

 ment being similar to that of the leech. To this 

 family belong the Myxine and the Lamprey. 

 So great is the force of adhesion exerted by this 



