860 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [142] 



is a predominance of circular fibers, which form an indistinct layer and 

 in which a division presently takes place, the outer part and the gran- 

 ular tissue which is outside of it sloughing off to form the collar. Part o*f 

 the circular lay er then goes to form the outer cuticular layer of the body 

 and another part goes to form the inner cuticular layer of the collar. 

 In sections made through the anterior part of the body, still within the 

 collar, the latter now appears as a concentric circle of dense granular 

 tissue with a few circular fibers. The tissues of the body proper are, 

 first, a thin cuticular layer; then a thick layer of spongy tissue with 

 irregular open spaces and a few longitudinal fibers interspersed; next 

 a layer of longitudinal fibers, into which most of the longitudinal fibers 

 of the neck are now collected. This layer is about 0.027 mm thick, and 

 surrounds a central core which is about 0.324 mm long, from margin to 

 margin, and 0.035 mm broad. 



Sections of longitudinal vessels lie at the marginal extremities of the 

 central core. Of these there are three principal ones near each margin. 

 Two of these, at each margin, have definite outlines; the other, at least 

 at first, is somewhat indefinite. In some sections they are oblong, the 

 largest about 0.01 mm in diameter; in others they are nearly circular and 

 as much as 0.016 mm in diameter. These longitudinal vessels appear first 

 in sections immediately behind the contractile bulbs, before the inner 

 core is differentiated. 



Anatomy of posterior segments. — In my former account of this species 

 I stated that the female genital aperture is lateral. In this I was mis- 

 taken, being misled by the median lateral aperture for the escape of 

 ova. A few segments were stained and cut into thin sections. In them 

 the vagina was traced from the ovary forward along the median line; 

 where it lay as a small tube, with short sinuous curves, to the base of the 

 cirrus bulb. It there turns abruptly towards the margin, and in some 

 can be traced for a short distance behind the cirrus bulb. It very soon 

 passes to the side of the bulb, and consequently in longitudinal sec- 

 tions disappears from view. The cirrus emerges not exactly on the 

 margin but a little way from the margin. The vagina appears to open 

 immediately beside the cirrus, between it and the margin, or, what is 

 more probable, the vagina and cirrus have a common marginal cloaca. 

 In some sections, which passed diagonally through the segment, the 

 tube of the vagina was seen lying close beside the cirrus bulb and near 

 its outer extremity. The cirrus, in these sections, is seen as a slender, 

 convoluted tube lying in the elongated bulb. The vas deferens is a 

 much convoluted tube, which lies in an irregular or pyriform mass in 

 front of the ovary. It enters the base of the cirrus bulb near the an- 

 terior edge of the segment. The ovary is centrally situated, about 

 ,36 mm broad and .16 mm long. In some of the sections it seemed to be 

 made up of elliptical lobules, each containing a number of polygonal, 

 often nucleated cells, each of the latter about .008 mm in diameter. 



In segments which did not contain ova the walls are quite muscular. 



