350 ROXIE A. WEBER. 



EXPLANATION OF PLATE I. 



Helodrilus caliginosus trapezoides. 



1. No. 95, showing union through five segments. 



2. No. 171, showing union through one segment. 



3. Section through the anterior portion of No. 95, showing the pharynx fused 

 and the extension of the nerve tissue almost entirely around the pharynx, b, cere- 

 bral ganglia; s, setae. 



4. A section through a more posterior region of the same monster. Vg, ventral 

 ganglia; DBv, dorsal blood vessel; VBv, ventral blood vessel; n, nephridium; 5, seta. 



5. A longitudinal section through No. 171, showing a portion of the cerebra' 

 ganglia b, and also parts of the ventral cords. 



