An American Earth norm of the Family Phreorifctidce. 109 



segment. The ventral seta3 continue throughout the body, at 

 first increasing in size backwards, and becoming very large and 

 long and strongly recurved at tip. At the middle of the worm 

 the imbedded part of the seta may extend into the coelom two 

 thirds the diameter of the body. The tips are obtuse and smooth, 

 and a circular ridge surrounds the seta below the middle. The 

 inserted portion is straight to the tip, from' which very numerous 

 distinct slender muscles radiate in all directions to the worms 

 wall. The dorsal setaj diminish in size and disappear between 

 the seventieth and eightieth segments, their occurrence becom- 

 ing irregular towards the last. In the middle part of the body 

 there is no trace of them nor of the glands for their de- 

 velopment. 



The large dorsal and subintestinal blood vessels are readily 

 seen in the living worm, as well as the contorted vascular 

 loops extending along the side of the intestine. The dorsal 

 vessel is contractile, and valved at the posterior portion of 

 each ccelomic space by four or five large, pale, nucleated 

 cells, so shaped and attached as to yield to forward pressure 

 but to close against backward. (Pl.VL, Fig. 3). This vessel di- 

 vides just behind the cerebral ganglion, each branch passing 

 outward and downward under the anterior end of the lateral 

 commissure, and then forward under the lateral part of the ce- 

 phalic ganglion, and upward and inward to the middle line in 

 front cf this ganglion, where the two branches from the oppo- 

 site sides nearly touch. Each then turns directly backward upon 

 itself and retraces the course just described, the direct and the 

 recurrent portions of the artery running parallel, a short dis- 

 tance apart, until beneath the anterior end of the commissure 

 again, where the vessel turns outward to the body wall. 



The lateral branches of the dorsal vessel (Pl.VL, Fig. 4) 

 are given off immediately in front of the posterior dissepiment 

 of each somite, and just behind the valves of the dorsal vessel. 

 Throughout the greater part of the body they run at first up- 

 ward and outward to the body wall, then irregularly forward 

 ( forming as they go a broad, downward loop on the side of the 

 intestine) to the front of the ccelomic space, where they turn 

 directly downward across the intestine, and backward along its 

 lower surface, again forming a broad, downward loop in the 



