192 CALIFORNIA ACADEMY OF SCIENCES. 



erected. In this way the external part of the penis can 

 be protruded from the genital cavity, which during the 

 operation becomes itself more or less erected. The 

 posterior sets of jnuscles contracting reverse these 

 movements, resulting in a withdrawal of the penis into 

 the genital chamber. 



Docophorus lari (Plate XIV, fig. 8). 



The chitinous genitalia in this species consist of a 

 large, thin, flat chitinous plate situated within the 

 abdomen close to the ventral wall, and an external, con- 

 ical tube with two articulated lateral arras. The plate 

 is rather short, being less than twice as long as wide. 

 Its greatest breadth is near its posterior end; it tapers 

 somewhat forward but has a wide rounded anterior ter- 

 mination. The external part is tubular and represents 

 an inner tube evaginated from the anterior end of the 

 genital cavity. Its walls are very thick and entirely 

 chitinous. In general shape it is, as stated, conical, 

 having the internal plate passing forward from the ven- 

 tral part of the anterior end. Its lateral outlines are 

 slightly convex. Posteriorly it terminates in a slender 

 median prolongation, at the extremity of which is the 

 external genital opening. Into the anterior end of this 

 part, dorsal to the internal plate, the ductus ejaculatorius 

 enters. Five processes surround the slender, parallel- 

 sided terminal tube. Two of them are dorsal, two lat- 

 eral — one on each side, and one ventral. The latter is 

 triangular in shape, rather elongated antero-posteriorly, 

 and has the more pointed apex pointed backwards 

 in the median line. The dorsal processes are much 

 longer than the ventral one. Each is a flat plate reach- 

 ing almost to the posterior end of the central tube. It 

 expands toward its middle and then tapers off again 



