62 THE STRUCTURE AND FUNCTION OF THE PROBOSCIS 



branch behind the distal extremities of the intermediate set. The branches 

 diverge widely behind those of the intermediate set, but do not articulate directly 

 with the discal sclerite. At each side of the figure this set is represented by 

 separate chitinous bars which do not unite to form definite teeth. 



The teeth of the inner set form the side walls of gutters whose floors are formed 

 by the branches of the intermediate and outer sets of teeth and the integument 

 covering them. Fluids drawn through the collecting tubes pass along the gutters 

 into the mouth. 



The tendinous chords described by Lowne (p. 395) are indicated between the 

 pseudo-tracheae. {From GTa.ha.m-Svn\th, yourna/ 0/ Ify^tene, 1911.) 



teeth, in fact all that area bordering the longitudinal sulcus, is 

 capable of being bent through a right angle. It is over these 

 highly flexible regions of the suctorial disc, which are invariably- 

 bent during the act of feeding, that the pseudo-tracheae are 

 converted into closed collecting channels. 



T/ie prestomal teeth. 



On each side of the prestomum is arranged a series of rows 

 of chitinous teeth, usually ten in number. The central rows 

 each consist of three teeth. The innermost teeth are the 

 strongest and are articulated at their proximal extremities on to 

 the chitinous side of the lateral plate of the discal sclerite, while 

 their distal free extremities are bifid. Except at their bases 

 they are free from investment with integument. The intermediate 

 teeth are longer than the inner and their distal extremities are 

 placed directly external to those of the inner set. Their distal 

 extremities are bifid. Immediately behind the free extremities 

 of the inner set these teeth branch, and the two branches pass 

 behind and to the sides of the inner set to be inserted into the 

 discal sclerite. The upper thirds only of these teeth are free 

 from integument. The outer teeth resemble the intermediate 

 set in their general shape and disposition, but are longer. 

 Their distal extremities are bifid, but their proximal branched 

 extremities are not inserted into the discal sclerite, but seem to 

 articulate with it indirectly through the intervention of plates of 

 chitin. Only the distal ends of the outer set are free from 

 integument. 



The arrangement of these teeth will be best understood by 

 reference to Fig. 22 which represents the teeth as seen from the 

 oral aspect. 



