670 ^V- G- MacCallum. 



of the coeca appears extraordinarily tliick and tlie lumen extremely 

 iiarrow. There is a quite tliick rauscular coat of circular and longitudinal 

 fibres and outside tliese there are numeroiis irreg-ular cells accom- 

 panying tJie coeca and sending" processes between the muscle bundles. 



The excretory System in this form is interesting in its arrange- 

 nient. bnt it is so closely associated with the parenchyma that that 

 nmst be first described. The worm is qnite translucent and Avithal 

 (luite tliick dorsoventrally. The translucency is seen on section to 

 depend largely on the structnre of the parenchyma. This is com- 

 püsed of ramifying cells whose nuclei are very inconspicuous and 

 sraall. The cell body is also rather attenuated, the main bnlk of 

 the tissue being- made np of great Spaces between the cells which 

 are filled with a coagulable fluid. This fluid is not everywhere of 

 the sanie consistence for while in some Spaces it is slightly granulär 

 and stains scarcely at all, in others it becomes niore dense and 

 assumes a pink stain. Finally there are several canal-like Spaces, 

 two on each side, dorsal and ventral to the intestinal coeca, Avhich 

 run tliroughout a large part of the length of the body and which 

 contain an especially dense colloid-like, pink-staining fluid. Tliese 

 canals seem to be actually lined by an endothelium-like layer of 

 flat cells but it does not seem possible to outline tliem clearly every- 

 where, and one receives the Impression tliat they communicate with 

 the other Spaces between the cells. Such canals or lacunae Surround 

 the anterior and posterior suckers which seem to be suspended 

 in them. 



Beginning at the extreme anterior end of the body there are 

 several canals with basement membrane and much convoluted wall 

 lined by high cubical or columnar or even bulbous cells which carry 

 a great deal of brown pigment. There are tliree of these canals 

 on each side anteriorly, but as they approach the posterior end they 

 unite into one canal on each side and eventually these trunks approach 

 the middle line and joining to form a thicker tube whose wall is 

 even provided with muscular hbres, the System finally opens at the 

 point in the median dorsal line just in front of the posterior suckers, 

 referred to above. This System of pigmented canals which can be seen 

 in the whole w^orni by transmitted light inust be regarded as the 

 excretory or water vascular System. Cf. Fig. A (page 674) in which only 

 the pigmented canals and the median excretory sac are represented. 



Now in sections it is seen that the canals filled with the red 

 staining colloid-like material stand in direct communication with 



