TUBIFEX. 389 



mouth. The worm is simply made use of in this case as 

 a substratum to which the Vorticellid becomes attached. 

 These Protozoa are very abundant on some individuals, 

 and completely absent from others, but, as a rule, when 

 present, they are confined to the posterior segments of the 

 body, those" which wave about freely in the water. 



The fact that Fungi often attack these worms was 

 recognised by Mcintosh (1871), who speaks of Fungi 

 growing on the dis-organised anterior segments, while 

 the posterior ones are in full activity. I have often 

 observed fully active worms which are infected with 

 Fungus growths, and it seems very probable that the 

 Fungus increases so much in quantity that it actually 

 causes the disintegration of the segments which are 

 attacked — the anterior segments are usually affected first, 

 but the growth may spread throughout the entire length 

 of the body. These Fungi appear, as a rule, to attach 

 themselves in or near to the setigerous sacs, for they are 

 usually to be seen emerging from between the two prongs 

 of the sigmoid setae, forming long, delicate filaments, 

 several of which may originate from the same seta-bundle. 



The internal parasites may be found in the 

 alimentary canal, sperm sac and body cavity. Mcintosh 

 states (1871) that he has found numerous examples of 

 Opalina amongst the sandy mud in the intestinal canal. 

 He gives figures of some of these specimens, which have 

 very diverse forms. These worms were captured from the 

 margin of the River Tay. It is interesting to note that, 

 although I have examined numerous worms from the 

 Thames both in sections and in the liviug condition, 

 I have never once found Opalina in the alimentary canal. 

 I have been more successful, however, in finding parasites 

 in ihe sperm sac and body cavity. During the summer 

 months of 1912, when the worm was really immature, 



