188 CALIFORNIA ACADEMY OF SCIENCES. 



The. External Male Genitalia. — The outer accessory 

 structures connected with the inner reproductive organs 

 have never been very carefully studied. Nitzsch (1818), 

 Piaget (1880, 1885), and Taschenberg (1882) described 

 them mostly as they appeared through the body-wall. 

 Piaget made a few dissections. The external organs con- 

 sist of two parts: (1) a simple or compound invagination 

 of the body-wall of the last abdominal segment, and (2) 

 chitinous parts developed in the walls of the invagina- 

 tion. In addition, however, there are muscles attached 

 to these parts, situated within the body, and which are 

 very important and sometimes very complicated 

 adjuncts of the copulatory organs. The following 

 descriptions represent all the genera of which males 

 could be obtained. 



Eurymetopus taurus (Plate XIV, fig. 5, plate XV, fig. 1). 



The male has nine abdominal segments. The last 

 tergum is very much narrowed from side to side, 

 forming a triangular terminal dorsal plate with the 

 apex, which is a little invaginated, projecting back- 

 wards. The sternum of the last segment, on the 

 other hand, is much enlarged, projecting much beyond 

 the corresponding tergum both posteriorly and lat- 

 erally as a large plate with slightly upcurved lateral 

 edges. Above this plate the top of the copulatory organ 

 may be seen projecting a little beyond the end of the 

 tergum. By separating these two plates a terminal 

 cavity of the abdomen is exposed, having the chitinous 

 penis lying along the middle line of its floor, and the 

 anus opening into the upper posterior part. This space 

 will be spoken of as the genital cavity, since it is evidently 

 formed to accommodate the reproductive function, and 

 since it contains the external part of the copulatory 



