No. 2.] STRUCTURE OF BIMASTOS PALUSTRIS. 475 



the male pore. Both pairs of orifices lie between the two 

 couples of setae, but closer to the ventral couple. 



The somites behind the genital protuberances narrow and 

 upon XXIII to XXVIII, inclusive, is a well-marked clitellum, 

 which is complete ventrally, although thinner, and usually- 

 showing the intersegmental furrows quite distinctly. 



Anteriorly, B. pabistris is of a deep pink color, owing to the 

 vascularity of its body-walls. The color becomes lighter ven- 

 trally, whilst posteriorly the walls are thin and pale, almost 

 transparent, the blood-vessels and intestine being readily seen 

 through them. 



The clitellum is clay-colored. 



The posterior region of this worm is readily broken, and 

 partially regenerated worms are frequently met with. 



Body-xvalls. — The body is covered by a cuticle of the usual 

 character, except in the regions immediately surrounding the 

 male pores, where it is either wanting entirely, or else is ex- 

 tremely attenuated and much interrupted. 



The hypodermis is as in Lumbricus and other terrestrial 

 Oligochaeta. 



The clitellum, as above stated, occupies somites XXIII to 

 XXVIII, inclusive. It is well marked, both in color and tex- 

 ture, and is continuous, though but two-thirds as deep, ven- 

 trally. The hypodermal layer is developed at the expense of 

 the muscular portion; both the circular and longitudinal mus- 

 culatures are much reduced in this region, the former, in places, 

 being almost obsolete in some specimens. 



In the clitellar tissue proper, the same cellular elements are 

 found as in the corresponding region of Lumbricus, the un- 

 modified hypodermal cells, however, being less numerous. 

 The outer third of its thickness is occupied mainly by some- 

 what flask or club-shaped cells, containing coarse, refractive 

 granules, which closely fill nearly the entire cell. The lower 

 portion of each cell is a nucleated and nucleolated protoplasmic 

 mass prolonged into a tail-like process, the ultimate fate of 

 which I could not determine. 



The deeper portions of the clitellum consist of long-necked, 

 club-shaped cells containing a clear or very finely granular 



