161 



resentative brain measured as follows : leng-th, 0.153 mm., width, 0.085 

 mm. A distinct neurilemma encloses the organ and is slightly thick- 

 ened on the posterior margin. Two pairs of strands attach the organ 

 to the bodv wall, one arising near the mid-lateral part and the other 

 from a latero-posterior position. In transverse section the brain is 

 almost circular. 



Pcptoncphridia. — Two of these organs (PI. XI, Fig. 39) lie ven- 

 trad to the digestive tract, one on either side of the median line. Each 

 opens independently into the cesophagus in a latero-ventral position 

 in the posterior part of IV. There is some variation in length. In 

 some specimens they extend into VII and in others only to VI. The 

 general structure is, however, the same. They lie parallel to the di- 

 gestive tract, and both gradually diminish in diameter towards the 

 terminus. They are roughly tuberculate in appearance and give off 

 short single tubular branches at irregular intervals. The branching is 

 much more marked at the posterior end, although even there it is 

 sparse. Anteriorly the branches are given off only at wide intervals, 

 are short, and show no secondary branching. 



Chyliis Cells. — Chylus cells occur in the wall of the intestine in 

 ^XIV-XVIII. As in certain other species of Fridericia previously 

 described, the epithelial layer of the intestinal wall in this region (PI. 

 XI, Figs. 38, 41) is composed of two distinct kinds of cells, the ental 

 epithelial cells, which line the lumen of the intestine, and the chylus 

 cells, which lie deeper in the intestinal wall and meet the lumen only at 

 points between the ental epithelial cells. The ental epithelial cells are 

 wedge-shaped, the larger ends being entad. In sections the smaller 

 ends appear to be inserted between the apices of the chylus cells either 

 singly or in groups of two, usually the latter. Each ental epithelial 

 cell contains a large elliptical nucleus in the ental end, and the surface 

 bordering on the intestinal lumen has numerous long cilia. The ectal 

 end is in contact with the perivisceral blood sinus. Each chylus cell 

 is flask-shaped, the broader end being ectad, and is about three times 

 as long as broad. The base is long and slightly truncate, the apex 

 rather pointed, exposing little surface to the lumen of the intestine, 

 and the sides of the cell converge gradually entad. The intracellular 

 canal extends the full length of the cell. Its apical half is straight or 

 nearly so, but the basal part often shows two distinct spiral turns. The 

 lining of this canal appears to be little more than a mere bounding 

 membrane. Only the apical half of the canal is ciliated. The re- 

 lation to the perivisceral blood sinus is intimate. i\s shown in figures 

 38 and 41 the surface of the base and from one half to two thirds 

 the length of the sides are in contact with the sinus. A distinct 



