408 University of California Publications in Zoology. [VOL. 6 



size. They are lined with a cuticula resembling that covering 

 the body, and are surrounded by a well-developed band of cir- 

 cular muscle fibres (circ. muse. I., pi. 11, fig. 60) resembling in 

 size and shape the cuticular longitudinal fibres of the body. Out- 

 side of this circular muscle layer is a mass of parenchyma fibres 

 passing in the same direction. Nuclei are scattered about irregu- 

 larly in the neighborhood of this layer, but often at some little 

 distance from it. 



In the larger of these canals, a large tuft of cilia projects 

 into the lumen, through a break in the cuticular lining, running 

 the whole length of the canal. These ciliated canals receive the 

 smaller non-ciliated ones. The non-ciliated canals are plainly to 

 be seen in the living animal in the lateral frills, in close relation 

 to the follicles of the vitellaria, emptying on the one side 

 (lateral) into a small non-ciliated "sinus terminalis" (Wag- 

 ener) and on the other side (medial) into a ciliated canal of 

 about twice their own diameter (pi. 35, fig. 20). Still further 

 mediad, near the base of the lateral folds, is a second ciliated 

 canal, of the same size and appearance as the first. In it, how- 

 ever, the waves of motion traverse the cilia in the opposite direc- 

 tion from that taken in the more lateral canal. Thus, if in the 

 outer one waves pass from anterior to posterior, in the inner one 

 they run from posterior to anterior. The motion is almost in- 

 credibly swift and very regular. 



The largest excretory canals lie within the central core of the 

 body, among the inner longitudinal muscles, the ovaries and 

 testes. Running the length of the body, on either side of the 

 uterus, is a very large ciliated canal, the largest in the body. The 

 structure of these canals is like that of the smaller peripheral 

 canal described above, except that the lining is thicker, the muscu- 

 lar layer better developed and nuclei more numerous in the neigh- 

 borhood of the wall of the canal. In no case has it been possible 

 to recognize any connection between the cilia of the canals and 

 the neighboring nuclei, such as was figured by Lonnberg (1891, 

 Taf. 3, figs. 39,40). 



Around the anterior margin of the acetabulum there is a 

 fairly well-defined ring-canal, receiving many small anastomos- 

 ing longitudinal branches. Its diameter and relations shown 



