Smith — Lake Superior Lumbriculids. 37 



to the "prostate" of M. asymmetricus, but relatively shorter and more 

 slender. This organ extends dorsad and laterad to a position near the open- 

 ing of a sperm sac in septum 10/11, where it is connected with the anterior 

 end of the sperm reservoir by a duct of diameter similar to that of the 

 penial organ (0.045-0.05 mm.). The reservoir is included within the 

 sperm sac of the atrial side of the worm and extends posteriad two to four 

 somites, the distance varying in different specimens. In the type specimen 

 it ends in somite 14. The wall of the reservoir includes a thin lining 

 epithelium; several thin laminae of muscular tissue of which the fibers 

 have a spiral direction, some to the right and some to the left; and a very 

 thin outer layer of longitudinal fibers. The spirally arranged fibers are 

 more nearly transverse than longitudinal, and the angles which they 

 make with each other and with those of the superficially placed longi- 

 tudinal series are approximately equal (60° or 120°). This arrangement 

 is very different from that in M. asymmetricus in which the chief mass of 

 muscle fibers have a slightly spiral course, but are nearly parallel with 

 the longitudinal axis of the sperm reservoir. The diameter of the reser- 

 voir is approximately one-fifth of that of the somites containing it and the 

 diameter of the lumen, midway of its length, is about one-third of that 

 of the reservoir. Connected with the wall by narrowed extensions are 

 numerous gland cells of large size which are similar to the "large prostate 

 cells" of Eclipidrilus frigidus described by Eisen (1895). There is no 

 large mass of gland cells related to the spermiducal pore, as in M. asym- 

 metricus (Smith, 1896:405). Paired sperm sacs extend posteriad from 

 septum 10/11 through four to six somites; in the type specimen at least 

 to somite 16. 



There are uniformly a pair of ovaries in 11 attached to septum 10/11, 

 and a pair of oviducal funnels and oviducts in the same somite, related 

 to septum 11/12. From 11/12 a pair of ovisacs extend posteriad a few 

 somites beyond the posterior ends of the sperm sacs, which are included 

 in the anterior part of the ovisacs. More commonly there is one sperma- 

 theca in 9, opening on the mid-ventral surface near the posterior boundary 

 of the somite, but in one specimen there is also a second spermatheca in 

 8, with opening similarly placed in that somite. The spermathecal ducts 

 have relatively small diameter and are sharply distinct from the large, 

 rather thick-walled sacs. The sacs often invade adjacent somites and 

 may be on either the right or left side of the alimentary tract. The diameter 

 of the duct is about 0.075 mm., while that of the sac is often more than 

 half of the diameter of the worm, and hence nearly ten times as great. 



Relationships of Mesoporodrilus lacustris. 



The relationships of M. lacustris seem very clear. In having a single 

 atrium opening on the mid-ventral surface, and asymmetrically arranged 

 spermathecae which also have median pores, its close relation to M. 

 asymmetricus is obvious. While agreeing with this species in various 

 other characters of generic rank, it is clearly distinguished by several 

 characters of specific grade. Two pairs of spermaries and spermiducal 



