202 



FILTER-BED XEMAS 



f erentiation occurs, 

 but the cells having 

 the coarser struc- 

 ture are more scat- 

 tered. They never- 

 theless are here 

 also commonly dor- 

 sal or sub-dorsal. 



What seems to 

 be a very long and 

 narrow tubular or- 

 gan (org f) exists 

 in ignavus. I have 

 been unable to de- 

 termine the func- 

 tion of this inter- 

 esting organ. The 

 mycelium of vari- 

 ous parasitic fungi 

 is not altogether 

 uncommon in the 

 bodies of fresh 

 water nemas, and 

 sometimes presents 

 highly deceptive 

 appearances, but it 

 . did not seem possi- 

 ble to me that this 

 tubular structure 

 could be other than 

 an integral part of 

 the Ironus. 



It is interesting 

 to note that the 

 most common spe- 

 cies of Ironus in 

 American filter- 

 beds are identical 

 with those of Eu- 

 rope. Ironus igna- 

 vus is widely spread 

 inthe United States, 

 as I have collected 

 it from spring, lake 

 and river waters of 

 many of the north- 

 ern states, from the 

 Atlantic as far west 

 as Colorado and 

 from widely vary- 

 ing altitudes. 



Fig. 5. It 



.TI&. a. 1 c//t lynuvux. Jiiiure- fjfj v 



tory pore and salivary glands as in /"*' 



longicaudatus, q. y. The differ- ''/ , 

 entiation of the intestinal cells , /* 



though marked is not so pro- /* 

 nounced as in longicaudatus. 



Common in filter-beds. See p. 212. /**'JH/ 



6 Ib H t 



