56 THE STRUCTURE AND FUNCTION OF THE PROBOSCIS 



TJie pseudo-tracJiecB. 



The pseudo-trache;E are deep furrows or incomplete mem- 

 branous tubes embedded, more or less deeply according to the 

 degree of its inflation, in the substance of the oral surface of the 

 labellum, but under any conditions projecting sufficiently to 

 produce distinct ridges. Along the apex of the ridge the wall 

 of the pseudo-trachea is lacking so that the interior of the tube 

 is in communication with the oral surface of the disc through a 

 very narrow zigzag fissure. The lumen of the tube is kept open 

 by means of incomplete chitinous rings running transversely 



Fig. 20. Fig. i\. 



Fig. 20 is a side view of a pseudo-tracheal ring. At its right-hand end the ring has 

 a flattened expanded extremity ; at its left-hand end a bifid extremity. The 

 opening of the longitudinal fissure is seen between the flattened end of the ring 

 and the tips of the forks. Tlie arrangement of the fold of integument forming the 

 interbifid groove is indicated by means of shading. (From Graham-Smith, 

 Journal of Hygiene, 191 1.) 



Fig. 21 represents two consecutive pseudo-tracheal rings, showing the relationship of 

 their bifid and flattened extremities, as seen from the oral surface of the disc. 



round the tube, each of which has one fork-like bifid extremity, 

 enclosing a rounded space between the prongs, and one extremity 

 slightly expanded and flattened so as to resemble the tail of a 

 fish. The rings are arranged in such a manner that along each 

 side of the central fissure the bifid extremity of one ring alternates 

 with the expanded extremity of the next ring. In consequence 

 of this arrangement, which is very clearly seen in preparations 

 treated with potash for the purpose of demonstrating the chitin- 

 ous structures, the margin of the pseudo-trachea at each side of 

 the central fissure has a deeply indented or scalloped appearance. 



