Premnodrilus palustris, 467 



sponding sperm-sac, and lies dorsad of the sperm-reservoir 

 and parallel with it (Fig. 3), one extending into XII and the 

 other as far as XVII. In two specimens, in which careful 

 measurements were made, the entire length of each sperma- 

 theca was a little over 3 mm., the greatest diameter being 

 .25 mm. The general form and proportions of these organs 

 can be readily seen in Fig. 2. 



Each spermatheca includes three distinct regions, which 

 may be designated respectively as duct, storage region, and 

 glandular region. The duct is about 1 mm. in length, and 

 has comparatively thick walls, which consist chiefly of longi- 

 tudinal muscle fibers. The muscular layer is thickest in the 

 middle of the duct and gradually thins out near the beginning 

 of the storage region. The diameter of both duct and lumen 

 is subject to considerable variation as shown by the following 

 measurements, which are very nearly the same for the two 

 spermatheca 1 most carefully studied. At a distance of 

 .25 mm. from the pore the diameter of the duct is .1 mm. and 

 that of the lumen .05 mm., and in this region the lining epithe- 

 lium is thrown into numerous high transverse folds, which 

 nearly fill the cavity. The diameter of the duct .4 mm. from 

 the pore is .1 mm., while that of its lumen is reduced to 

 .02 mm. From this point to the beginning of the storage 

 region the diameter of the duct gradually decreases to 

 .045 mm,, while the lumen at first increases to .045 mm., 

 next decreases to .02 mm., and then enlarges into the cavity 

 of the storage region. The storage region is about .5 mm. 

 in length and has a diameter of .15 mm. for the first half, 

 then widens out to .22 mm., and is next constricted to 

 .14 mm. where the division between the second and the third 

 region occurs. Its walls are quite thin in the part nearest 

 the duct, but gradually become. thicker and more glandular 

 and like those of the third region. This third, or glandular, 

 region is about 1.85 mm. in length, and its diameter is pretty 

 nearly uniform, varying only from .2 mm. to .25 mm., while 

 that of its lumen varies from .12 to .18 mm. The storage 

 region and the glandular region are not sharply differentiated, 

 but the former is filled with spermatozoa while the latter con- 



