618 



The clitellum is on XII and XIII and is distinctly developed. The 

 cells (PI. XCVIII, Fig". 3) are all of the same kind. The first dorsal 

 pore is in VII, and each pore has a mid-dorsal position in the middle 

 of its somite lengthwise. 



Brain. — The brain (PI. XCVIII, Fig. 4) is in the anterior part of 

 II but projects slightly into I. The length is about one and one fourth 

 times the width. The anterior margin is moderately concave, while 

 the posterior margin is strongly convex. The lateral margins are 

 nearly parallel. Two pairs of supporting strands extend from the 

 lateral margins to the body wall. 



Peptonephridia {Salivary Glands). — A pair of these organs open 

 into the ventral side of the digestive tract in the anterior part of 

 IV, close to the septum. They extend caudad through IV and V and 

 a short distance into VI. Each gives off a number of branches at 

 irregular intervals throughout its length. 



Chylns Cells. — The chylus cell region is that part of the intestine 

 included in XIII-^ XVIII. Here the intestine is lined with the 

 layer of ental epithelial cells, which are ciliated and approximately 

 rectangular in section, and each of these cells contains a large spheri- 

 cal nucleus. The chylus cells lie deeper in the intestinal wall^ and 

 open between the cells of the ental layer into the lumen of the intes- 

 tine. They are long, rather narrow, and broader at the bases than 

 at the apices. The intracellular canal (PI. XCVIII, Figs. 6, 7) is 

 ciliated and nearly straight in the apical part, but elsewhere it is non- 

 ciliated and somewhat tortuous, especially in the broad basal part. It 

 is surrounded by a definite layer of cytoplasm of uniform thickness, 

 which is more hyaline and stains more intensely than the finely granu- 

 lar and deeply staining adjacent part. The two kinds oi cytoplasm are 

 sharply differentiated. The elliptical nucleus lies in the base of the 

 cell in the angle formed at the chief bend of the canal. The cell 

 walls are indistinct, and it is somewhat difficult to determine the 

 exact line of demarcation between adjacent cells. However, suffi- 

 cient details of structure can be made out to prove that these cells 

 are definite units and that each canal is confined entirely within the 

 limits of a single cell. There is some variation in the form of the 

 chylus cells, since near septa and sometimes in the lateral walls of 

 the intestine they are rather short, while between septa they may be 

 rather long and slender. However, in all cases the general structure 

 and the arrangement of parts are uniform. Interstitial cells are ab- 

 sent. Certain considerations relating to the chylus cells will be taken 

 up in another part of the paper (p. 626). 



Ncphridia. — The first pair of nephridia are related to VI/VII. 

 The anteseptal part (PI. XCVIII, Fig. 5) of each nephridium is 



