156 



long, well-developed branch which extended cephalad and terminated 

 anterior to the opening of the peptonephridium. The structure of this 

 branch is identical with that of the main trunk. This is probably an 

 accidental condition, since it occurred in only one specimen and only 

 on one side. 



Chylus Cells. — ^The chylus cell region of the intestine occupies 

 XV-XVIII in all of the specimens examined except one, in which a 

 few chylus cells appear in the posterior part of XIV. Cells of two 

 kinds are present (PI. X, Fig. 33), the chylus cells and the ental 

 epithelial cells. The chylus cells form a continuous layer. They are 

 flask-shaped, the broader ends being ectad. The base of each is more 

 or less truncate and the sides converge gradually entad. The apical 

 half of the intracellular canal is straight, but the basal half is spiral 

 and appears sigmoid in section. This intracellular canal is lined by 

 a relatively thick specialized layer of cytoplasm which is everywhere 

 uniform in thickness and structure. The canal is ciliated for the 

 greater part of its length. The blood sinus comes in contact with 

 little more than the basal end of each chylus cell. The ental epithelial 

 cells are long and trumpet-shaped, the broad end being ental. Their 

 ectal ends are inserted between the apices of the chylus cells. In 

 longitudinal sections usually but one epithelial cell appears 

 between each chylus cell and its neighbor. The ental surface of these 

 cells is ciliated. Interstitial cells are absent. There appears to be a 

 distinct difference in the structure of the chylus cells and the ental 

 epithelial cells as indicated by the staining reaction. In the form.er 

 the cytoplasm is somewhat granular, while the cytoplasm of the ental 

 epithelial cells is more homogeneous and more dense. 



Blood Vascular System. — The blood-vessels in the specimens of 

 this species remain better distended than in the others examined, mak- 

 ing it possible to follow them and to study the chief vessels. The 

 system (PI. IX, Fig. 25) consists of the usual dorsal longitudinal ves- 

 sel, the ventral vessel, and the transverse vessels which connect them, 

 these latter forming loops around the anterior part of the digestive 

 tract. The dorsal vessel arises from the perivisceral blood sinus in 

 XX. It shows distinct enlargements in each of the somites posterior 

 to the clitellum. From its origin it extends cephalad, parallel to the 

 digestive tract, with which it maintains a more or less close relation 

 throughout its course. In the anterior region it lies between the brain 

 and the buccal cavity, and is so reduced in diameter that it requires 

 high magnification to follow it. At a point immediately under the 

 anterior part of the brain it divides into two trunks, one passing to 

 the right and the other to the left of the digestive tract, and both ex- 



