NO. 6 GRASSHOPPER ABDOMEN SNODGRASS 69 



between the inner faces of the anterior apodemes of the lateral plates. 

 The compressors of the ejaculatory sac are broad plaques of fibers 

 closely applied to the lateral walls of the endophallus (C, E, 284) ; 

 each arises on the entire outer wall of the lateral endophallic plate, 

 and its fibers converge ventrally to their insertions on the lateral wall 

 of the ejaculatory sac. In some cases a distinct branch of this muscle 

 takes its origin on the endophallic apodeme (fig. 29 C, 284a). The 

 ejaculatory duct has a strong sheath of circular fibers (fig. 25 E, 28^=]) 

 extending to the membranous terminal sac. 



The function of the endophallic muscles is to regulate the gonopore, 

 /. e., the aperture of the ejaculatory sac into the spermatophore sac, 

 and to drive the spermatophores through the gonopore, through the 

 spermatophore sac of the endophallus, and through the phallotreme 

 cleft of the aedeagus. If the endophallic cavity is opened from above 

 by cutting its dorsal wall, and the lateral plates are spread apart (fig. 

 33 C), the slithke gonopore {Gpr) is to be seen in the floor of the 

 spermatophore sac between the posterior ends of the convergent 

 gonopore processes {y) of the lateral plates. The gonopore processes 

 are hinged to each other by points of contact just before the anterior 

 end of the gonopore; as a consequence, an approximation of the 

 endophallic plates, produced naturally by a contraction of the muscle 

 between their anterior apodemes (fig. 25 E, F, 28s), results in an 

 opening of the gonopore. 



The endophallic mechanism is well illustrated in Mcrmiria maculi- 

 pcnnis (fig. 29 E, F). When the lateral plates are separated, as in the 

 ordinary state (E), the gonopore {Gpr) is closed to a narrow slit; 

 but when the plates are brought together (F) the gonopore becomes 

 a widely open aperture. Immediately beneath the gonopore is the 

 membranous ejaculatory sac (fig. 25 G, H, ejs), which is a terminal 

 enlargement ot the ejaculatory duct. The compressor muscles inserted 

 on the lateral walls of the ejaculatory sac (C, E, 284) probably 

 contract in unison with the compressor muscle of the endophallic 

 plates, and force the spermatophore from the ejaculatory sac through 

 the open gonopore into the spermatophore sac. The passage of the 

 spermatophore through the spermatophore sac is not so easily ex- 

 plained, in the absence of direct observations on the action of the endo- 

 phallic apparatus, and it seems probable that the endophallic muscles 

 must produce movements of the endophallic walls other than those con- 

 cerned with the opening and closing of the gonopore and the com- 

 pression of the ejaculatory sac described above. 



The male genitalia of the Tetrigidae, by comparison with the 

 acridid organs, are not only very simple in structure, but, as observed 



