2 54 



RUCKER. 



[VOL. I. 



glands, are always on the third or fourth posterior appendages. 

 The only specimen with twenty-five pairs of legs, which did not 

 have these tubercles, was opened and found to be a female. 

 The position of these papillae can best be seen from Fig. 2, 

 which is a camera lucida drawing of the left fourth leg. Fig. i 

 is a drawing of the ventral surface of the posterior end of an 

 animal 2.4 cm. in length. At first sight the fourth or third 

 leg may appear to have only one papilla or none at all, but on 

 closer examination the tip of the papilla will be seen to be sur- 

 rounded by a circular ridge. Sections through these posterior 

 legs of different individuals show that the tubercles are of uni- 

 form development in all males, and that they can be retracted 

 or protruded in the living animal. The section also shows that 

 the papillae are retracted only by involuntary muscle fibers 

 inserted on these papillae. Fig. 4 represents a section through 

 the fourth leg. The inner papilla is protruded, while the outer 



AC. a 



Cr 3 0. 



--^w^ ' Hv > 

 /; . : 



Pa* 



FIG. 4. 



one is partially withdrawn. Fig. 5 is a section through the 

 third leg, showing the inner tubercle more retracted than the 

 outer one in Fig. 4. This tubercle has about reached its limit 

 of retraction. The outer papilla was cut to one side, so as to 



