248 BENEDICT. [Vol. XVI. 



a diameter of .012 mm., while the walls gradually increase in 

 thickness. Its course is a most intricate one, coiling and 

 twisting, and not confined to any particular part of the pouch 

 (PI. XVI, Fig. 17). Its course is not identical in different 

 proglottids, but all have much the same complicated twisting. 

 At about the middle of the course of the vas deferens in the 

 pouch a delicate cuticula, lining the cavity, makes its appear- 

 ance ; the longitudinal muscle fibers have become more promi- 

 nent, forming a well-defined layer, and circular muscles are first 

 plainly seen. Proceeding distally, the cuticula constantly but 

 slowly increases until, at the male genital opening, it is con- 

 tinuous with the body cuticula, and of equal thickness. 



The windings of the vas deferens are invested with a delicate 

 structureless tissue, which is very elastic. It wraps the coils 

 of the duct and holds them in a constant relation to each other, 

 but is connected with the walls of- the pouch only by delicate 

 filaments. 



The distinction between vas deferens and cirrus is simply a 

 matter of size. The structure of vas deferens within the pouch 

 in its distal half is as follows (PI. XVI, Figs. 18 and 20): lining 

 the lumen, which is about .015 mm. in diameter, is the cuticula, 

 .002 mm. thick, and quite regularly cast into folds, like the bel- 

 lows of a camera (PI. XVI, Fig. 20, ^/.). Without the cuticula 

 is a very minute layer of transverse muscle fibers, which follows 

 exactly the contour of the transverse folds (PI. XVI, Fig. 20, 

 w.j.). The longitudinal muscle layer, which lies next, is of 

 unequal thickness, dipping down into the folds (PI. XVI, Fig. 

 20, mp). Above the muscle layers comes a loose layer, con- 

 taining pyriform glandular cells, with narrow processes pro- 

 jecting down through the muscle layers, beyond which they 

 could not be traced (PI. XVI, Fig. 20, cl.gl). Surrounding the 

 entire duct is a delicate single layer of flattened epithelial cells 

 with prominent nuclei (PI. XVI, Fig. 20, <?/.). 



The last coil of the vas deferens brings its distal end back to 

 the proximal end of the pouch near the ventral side. .A sudden 

 enlargement to .07 mm. in long diameter then takes place, and 

 the duct bends upward and outward (PI. XVI, Fig. 17). The 

 cirrus begins at the sudden enlargement, which is slightly bulb- 



