440 CALIFORNIA ACADEMY OF SCIENCES. 



All have their concave borders facing one another and 

 the center from which they spring. Along the convex 

 surface of each is a fringe of cilia inclined distally. The 

 rest of the pad is covered by short, thick projections, 

 lying with their long axes parallel to the surface and 

 curving over to the dorsal side, where they become scale- 

 like in form. Between this hypopharynx and the labium 

 is a fold of membrane from which project the anterior 

 ends of two other structures. There are two chitinous 

 rods (plate lx, figs. 6, fk, and 12) whose anterior forked 

 ends project through this fold and lie beneath and a little 

 external to the hypopharynx. They may be exposed by 

 removing the labium. Each lies ventral to all the other 

 organs in the head. Posteriorly they diverge from each 

 other and pass backward, ventral to the lower edge of 

 the tentorium, and are attached to the ventral wall of 

 the head by muscles. They are very slender and del- 

 icate on account of their thinness and being not very 

 strongly chitinized. Anteriorly each is rather expanded 

 and flattened dorsoventrally, but posteriorly becomes 

 narrower and more cylindrical. The outer prong of 

 the anterior bifurcation is wide and thin, the other is 

 longer, narrower, a little curved outwardly, and rather 

 more chitinous than any other part of the whole rod. 

 The bifid part projects out of the fold as described, but 

 very little if any of the shaft. The cuticle covering the 

 fold is continuous with that over the pads on the fork of 

 the hypopharynx, and is covered by small sharp-pointed 

 papillae, having enlarged bases, and projecting forward. 



