374 H. s. PRATT, 



pharynx. This organ has a length of 0.03 mm and leads into the 

 oesophagus, which, on its part, has a length of 0.03 mm, divided into 

 a constricted, narrow, anterior portion with a length of 0.009 mm, 

 and a wide posterior portion, with a width of 0.021 mm. The bifur- 

 cated portion of the intestine passes posteriad to the region of the 

 appendix: its diameter near its forward end is 0.018 mm and towards 

 its hinder end it is somewhat greater. 



The histology of the system is in no way unusual: it is of interest, 

 however, that the epithelial lining of the intestine does not appear 

 at the point of its bifurcation, as is common, but at the level of the 

 acetabulum, some distance back of this point. 



I have already mentioned the fact that I have never seen one of 

 these worms attached by either sucker to its host. Animals killed 

 in their hosts have often the oral sucker, pharynx, and forward 

 portion of the intestine filled with a clear, homogeneous fluid, which, 

 stained with eosin, becomes a deep red; and all the animals which 

 were sectioned, both those taken free-swimming and those enclosed 

 within Copepods, have lesser portions of the same substance in the 

 limbs of the intestine. I think it is the blood of the host which 

 the worms have sucked in, without, however, attaching themselves 

 by means of either sucker to the host's body, and which constitutes 

 their food. 



Nervous System. 



This system is well developed in the worm under discussion. 

 The broad, supra-oesophageal commissure, with a width of 0.007 mm, 

 extends across the narrow, anterior portion of the oesophagus, im- 

 mediately back of the pharynx, and connects the supra-oesophageal gan- 

 glionic masses (PI. 27, Fig. lis. 6r.). These are two distinct swellings 

 just posteriad of the pharynx, each with a width of 0.012 mm. From 

 them two broad nerves, each 0.01 mm wide, pass posteriad to the 

 hinder part of the body; two narrower nerves, each 0.007 mm wide, 

 also pass anteriad close to the surface of the pharynx and oral sucker 

 to the extreme forward end of the body. These latter nerves gra- 

 dually diminish in diameter and at their forward ends are reduced 

 to a fraction of their original width: at the point of juncture of the 

 pharynx and sucker, however, they swell to form a second pair of 

 ganglia (PI. 27 , Fig. 1 1 P. 6r.) the diameter of each of which is 

 0.075 mm. 



The histology of these nerves is simple. The central portion of 



