66 W. N. F. WOODLAND 



internal longitudinal muscle-layer and the dorsal anchor-cells 

 and fibres of the boring muscle ; the second series comprises 

 the similar transverse channels situated on the ventral side of 

 the body — the ventral transverse channels (PI. 3, 

 figs. 4, 6, VTc) ; the third comprises those channels which 

 arise from each lateral main channel on its dorsal side and turn 

 outwards towards the outer edge of the body — the dorsal 

 external channels (PI, 3, fig. 4, dec); and the fourth 

 comprises the similar outwardly directed channels which 

 arise from the ventral side of the lateral main channel— the 

 ventral external channels (PI. 3, fig. 4, vec). In many 

 and perhaps in most cases, the dorsal external channels and the 

 ventral external channels join together to form a lateral 

 excretory loop (PI. 3, fig. 6, lel), but in other cases the 

 two channels do not appear to communicate. Thus, in its main 

 plan, the excretory system consists (1) of two lateral main 

 channels which unite posteriorly to form a single exit channel 

 which opens to the exterior at the posterior extremity, and 

 (2) of subsidiary smaller channels which take the form, roughly 

 speaking, of three series of ' rings ' — the axially situated series 

 of flattened ' rings ' formed by the dorsal and ventral transverse 

 channels, and the two lateral series of ' rings ' arising from 

 and lying external to the lateral main channels. It must be 

 mentioned, however, that the upper and lower halves of these 

 ' rings ' very rarely lie in the same transverse plane — they only 

 form a ' ring ' when a considerable thickness of the body is 

 viewed end-on. In one worm measuring about 40 mm. in 

 length I observed that in 5 mm. of this length approximately 

 21 external channels were given off from one of the lateral 

 main channels — about 150 in the entire length of the worm. 

 Apart from this system of channels I have been unable to 

 discover any other portion of the excretory system, though 

 I have searched most carefully, in both transverse and longitu- 

 dinal series of well-fixed sections, for flame-cells. According 

 to Hein and Cohn flame-cells exist in A. folia cea in large 

 numbers, and the former author figures them ; but these 

 statements need confirmation, since Hein is possibly mistaken 



