212 CALIFORNIA ACADEMY OF SCIENCES. 



from that of the male in not being situated in the 

 terminal segment of the body, but by being found as an 

 invagination of the ventral body-wall several segments 

 forward. It also does not contain the anal opening, 

 this being situated terminally in the last segment. 



The external parts of the female are much the same 

 in all forms and the female Menopon titan may be 

 described as a type of the whole order. Grosse 

 describes the female organs of this form, but only very 

 briefly, and he says nothing at all of the external parts. 

 The sternum of the eighth abdominal segment is con- 

 siderably modified. It consists mostly of a large 

 depressed plate (plate xvii, fig. 7, pi) produced on each 

 side into two ventrally projecting ridges divergent 

 behind. The posterior border is free, above it is the 

 external genital opening (gc), a narrow transversely 

 elongated aperture. It opens into a cavity, the genital 

 chamber, situated above the plate. The structure is 

 best studied by means of transverse and longitudinal 

 sections. Longitudinal sections (plate xvii, fig. 6) show 

 that the genital chamber (gc) is formed as an invagi- 

 nation of the sternum of the eighth abdominal segment, 

 a short distance in front of the posterior border of the 

 latter. The vagina (v) opens into the upper part of its 

 anterior end by a terminal downward curvature. It is 

 lined by a continuation of the chitinous wall of the 

 body. Transverse sections (plate xvii, figs. 1-3) show 

 that the depressed plate of the eighth abdominal ster- 

 num is W-shaped. The tergum of the segment forms a 

 large, continuous, arched plate extending on each side 

 to the lateral edge of the body. Here a non-chitinized 

 line occurs, separating the tergum from a pleural chi- 

 tinization situated laterally on the ventral aspect. The 

 inner edges of these are united by unchitinized spaces 



