THE EXO-SKELETQN OF THE PROBOSCIS. 



145 



dorsal and proximal surface of the disc, and the two lips lie 

 flat, the walls of the prestomum being thrown into the same 

 plane as the surface of the disc. 



Fic. 31. — Details of the Oral Sucker : /, A section through the disc just in front of 

 the prelabrum : x, cavity of the prestomum ; y, cavity of the mouth ; a, dorsal 

 seam formed by a bead and furrow ; s g, labial salivary gland ; J, duct ; //;, 

 thyroid cornu ; / furca ; t c, tendinous cord ; j, cavity ; //, hypodorm cells. 2, 

 A similar section in a more anterior plane passing across the pseudotrachea; : x, 

 preslomal cavity and the bases of the teeth ; t c, tendinous cords ; pst, pseudo- 

 trachea;. J, A section through the junction of the theca and the oral sucker : 

 / furca ; £■, elastic ligament ; /, poculum, with labial glands on either side ; 

 h s, hypoglossal sclerite ; //, extremity of the prelabrum. 4, A pseudotracheal 

 vessel and the prestomal teeth and folds. 5, An isolated ring of one of the 

 pseudotracheK. 



The distal surface of the disc may therefore be described as 

 consisting of two parts, the prestomal and the discal. 



The prestomal portion is formed by the discal sclerites and 

 the teeth and folds of the prestomum (Fig. 31, 4) with the 

 inner orifices of the pseudotracheaj between them. 



