

TUBIFEX. 309 



band in each segment, forming an incomplete ring around 

 it and giving the worm a striped appearance. 



If specimens of both worms are examined under the 

 microscope, it will be seen that the setae are different, 

 Tubifex showing two kinds of setae, capilliform and 

 sigmoid, while Limnodrilus has only sigmoid. 



If the receptacle in which the worms are being kept 

 is suddenly jarred with a sharp knock, they all 

 simultaneously contract, hiding themselves almost 

 completely in the mud. Tubifex rivulorum is also 

 sensitive to light, for, if a bright beam from an arc lamp 

 be projected through the water on to the mass, all the 

 worms belonging to this species contract instantly and 

 disappear. Limnodrilus udekemianus appears to be 

 unaffected by the light, for the posterior end of the body 

 still continues to wave about in the water. 



If individuals of both species be placed on a slide, 

 it is possible to distinguish them by their movements. 

 Tubifex rivulorum is much more rapid in its movements, 

 and retains its activity much longer than Limnodrilus 

 udekemianus after being deprived of the mud in which 

 it lives. 



EXTERNAL CHARACTERS. 



Tubifex rivulorum is a small worm varying from 

 30-50 mm. in length, and is of a bright red colour. The 

 colour is due to the presence of red blood, which is clearly 

 visible through the transparent body wall. The worm is 

 bluntly pointed at both ends, the widest part of the body 

 being in the anterior third. The body is divided 

 throughout its length into a number of segments, all quite 

 clearly marked off from one another, and decreasing in 

 size towards the posterior end. The number of segments 



