108 PROCEEDINGS OF THE NATIONAL MUSEUM vol. m 



The entii-e gonopod structure can be protruded from the bod}^ by 

 the contraction of a pair of muscles that originate near the ventral 

 ends of the pleurotergite of segment 7 and insert on the gonopod at 

 the ends of the sternite (fig. 2,6). Retraction of the genital apparatus 

 into the bod}^ cavity is accomplished by large muscles that originate 

 on the dorsal side of the pleurotergite and insert on the distad ends 

 of the sternal apodemes. These two sets of muscles appear to be 

 common to the gonopods of many helminthomorphous diplopods, and 

 seem to be homologous to sunilar muscles motivating the free sternites 

 of such orders as the Chordeumida. 



The muscles that originate on the gonopod apparatus itself are 

 not numerous but provide for a gi-eat degree of activity. They are 

 most easily seen in caudal aspect, the accompanying figures (fig. 2,h-d) 

 showing several successive stages of dissection as well as a cleaned 

 gonopod for easy reference to hard parts. 



The following list designates the muscles and describes their func- 

 tions : 



1. A large, fusiform muscle originating on the caudal side of the 

 posterior apodeme and inserting on the base of the posterior gonopod 

 just mesiad to the pivot joint. Contraction causes the distal end of 

 the gonopod to swing proximomcsiad. 



2. Similar to 1 but originating on the anterior side of the apodeme. 

 Function is the same. 



3. A long slender muscle originating at the tip of the anterior sternal 

 apodeme and inserting on the base of the posterior gonopod near its 

 mesial end. Its contraction would provide extra power in support 

 of muscles 1 and 2, and likewise prevent uncontrolled protrusion of 

 the posterior gonopod by the contraction of 4. 



4. A large, flat, twisted muscle, originating along the caudal edge 

 of the anterior coxite, and inserting on the anterior face of the posterior 

 apodeme. Contraction would result in extrusion of the entire posterior 

 gonopod apparatus, the twisting presumably turnmg the gonopod into 

 a position to facilitate its escape from the gonocoel. 



5. A long slender ligamentous-type m.uscle origmating on the 

 anterior sternal apodemes and extending mesiad over 4 to join the 

 caudal extension of the vinculum. The function of 5 is to provide 

 stability for the caudal extension as well as to hold twisted muscle 4 

 in correct position during its contraction. 



6. A small, short muscle originatmg on the tip of the coxal apodeme 

 and inserting on the outer end of the base of the posterior gonopod 

 (fig. 2,d). The muscle would retract the gonopod to get it back 

 into the gonocoel. 



7. A small slender muscle running from the anterior side of the coxal 

 apodeme to the mesial end of the posterior gonopod and serving the 

 same function as 1 and 2, but, judging from its origin on the coxal 



