114 



THE VITAL FUNCTIONS. 



the TcBiiia has orifices of this kind in each of its 

 jointed segments : the Ascaris and the Earth- 

 worm have each a simple mouth. The margin 

 of the mouth is often divided, so as to compose 

 lips ; of these there are generally two, and in 

 the leech there are three. In some rare cases, 

 as in the Planaria, there is, besides the ordinary 

 mouth, a tube also provided for suction, in a dif- 

 ferent part of the body, and leading into the 

 same stomach.* 



When the instrument for suction extends for 

 some length from the mouth, it is generally termed 

 ^proboscis: such is the apparatus of the butterfly, 

 the moth, the gnat, the house fly, and other 

 insects that subsist on fluid aliment. The pro- 

 boscis of the Lepidoptera, (Fig. 266), is a double 

 tube, constructed by the two 

 edges being rolled longitudi- 

 nally till they meet in the 

 middle of the lower surface, 

 thus forming a tube on each 

 side, but leaving also another 

 tube, intermediate to the two 

 lateral ones. This middle 

 tube is formed by the junction 



sucking' disks are not perforated, and do not perform the office 

 of mouths ; and the true mouth for the reception of food is single. 

 Cuvier discovered an animal of this class furnished with above a 

 hundred of these cup-shaped sucking organs. See Edinburgh 

 Pliilos. Journal, XX. 101. 



» Phil Trans, for 1822, 442. 



