•SOME AQUATIC WORMS, ETC. 211 



tubular vessels, one above, the other below the tortu- 

 ous intestine. The upper, or dorsal one, has con- 

 nected with it near the anterior end of the body two 

 little contractile hearts, one on each side, which can 

 be seen through the hyaline animal throwing out the 

 blood with considerable force. The two vessels are 

 connected with each other by smaller branches, a pair 

 in each segment or body-ring, one being on each side. 

 There is also on each side of the body^ — two in each 

 segment— ^a narrow colorless tube, ciliated within, and 

 resembling those found in Nais and in other aquatic 

 worms. They are most conspicuous in the posterior 

 rings, and are supposed to represent kidneys in func- 

 tion. 



Tiibifex is reproduced by eggs, which probably 

 make their escape after the parents' death, and after 

 the body has fallen to pieces, as the living creature 

 has no natural passage for their exit. Huxley, how- 

 ever, says that they pass out through the segmental 

 organs — the ciliated tubes referred to in the preceding 

 paragraph. 



II. NXis (Figs. 153, 154). 



The body of Nais is whitish or yellowish and usually 

 very active. 



The podal spines and bristles are each arranged in a 

 row on both sides of the worm, the bristles near the 

 front end usually being longest. Each cluster of 

 ' ' podal spines contains four or more. 



The mouth is round. The front border of the body 

 bears numerous fine, short hairs. Two dark or black 

 eye-spots are generally present, one on each side in 

 advance of the mouth. The blood is red. 



