194 CALIFORNIA ACADEMY OF SCIENCES. 



of acting as a guard to the penis, or they may also 

 serve as levers to prevent the latter from being pushed 

 back into the genital cavity. The penis, however, is 

 otherwise very much the same as in those forms where 

 movable rods are absent. 



Nirmus pacificus. 



The penis is very similar to that of Docophorus lari. 

 The internal part is a wide plate which tapers slightly 

 forward and ends anteriorly with a wide rounded out- 

 line. The proximal half of each lateral margin is 

 slightly convex and very thickly chitinized, so that the 

 two give the appearance of a pair of curved prongs 

 reaching forward into the body cavity, since the median 

 part of the plate is comparatively very thin and trans- 

 parent. Between the internal plate and the outer parts 

 is a thickened portion common to both. The external 

 penis consists of two lateral curved rods articulated to 

 the base of the median external part. When the penis 

 is retracted within the genital chamber, these two rods 

 extend backward with their tips approximated and 

 their concave edges turned toward each other. When, 

 however, the penis is protruded, the rods turn forward 

 over the back of the insect and become rotated outwards, 

 so that their convex edges are toward each other and 

 their tips divergent. The median external part is pro- 

 longed terminally into a slender, tapering, chitinous 

 tube, which appears to bear at its end the genital 

 opening. Surrounding this are five processes which 

 arise near its base and are much the same as those of 

 Docophorus lari. On the dorsal side is a pair of rather 

 long slender plates, on the ventral side a slender 

 median rod, and on each side a rather large, outward- 

 turned process reaching a little beyond the extremity of 



