160 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



The wall of the vesicle is uniformly very thin and transparent in all 

 parts except immediately around the orifice of the duct, where it is 

 somewhat thicker; but there is no muscular sphincter at this point. 

 The histological structure of the wall is described in another connec- 

 tion (pp. 166, 167). 



At the anterior end of the vesicle, at a point on a line with the me- 

 dian border of the hilus and a little in front of the anterior edge of the 

 gland, there is an orifice which opens into the duct leading to the exte- 

 rior (Plate 1, Fig. 1, of. i.). This orifice is circular, or slightly oval, and 

 1 to 1.5 mm. in diameter. It is noticeable that it retains its shape when 

 the walls of the vesicle are collapsed. 



The duct is a thin-walled tube, oval in cross section, — being slightly 

 flattened dorso-ventrally, — and lies wholly within the antenna. From 

 the orifice in the vesicle it extends downward and slightly forward and 

 outward for a distance of 5 to 7 mm. Its average diameter through 

 this region is 2 mm. At the level of the coxo-basal joint the duct turns 

 abruptly through an arc of about 45° in a parasagittal plane of the body, 

 and runs downward and backward to the tubercle on the ventral face of 

 the coxopodite, through which it opens to the exterior. Its diameter 

 through this second part of its course is somewhat greater than in the 

 first part, but diminishes noticeably as it enters the tubercle. There is 

 a slight dilatation at the point where the tubules from the white lobe 

 enter. The entire length of the duct is not over 1.5 cm., and its aver- 

 age diameter is perhaps 2.5 mm. 



I find no sphincters or other muscular structures in or around the 

 wall of the duct, other than the muscles of the antenna, among which it 

 runs. It seems, then, that the ejaculatory process, by which the secre- 

 tion of the gland is sometimes forced out of the external orifice, cannot 

 have its origin in any intrinsic action of the duct. It may arise from 

 concerted action of the muscles of the antenna, but since no especially 

 active movement of the antenna has been noted in connection with this 

 function, it is probable that the force producing such ejaculation has its 

 seat in the muscular walls of the vesicle, the duct being passive. 



The external orifice of the duct is situated at the apex of a truncate 

 conical tubercle, which rises from the general ventral surface of the cox- 

 opodite of the second antenna. This tubercle is nearly in the midventral 

 line of the appendage. It does not stand perpendicular to the general 

 surface, but its axis is inclined slightly forward and medianward, so that 

 if the antennae were at rest in the horizontal position, the axes of the 

 two tubercles prolonged would intersect at a point in the sagittal plane 



