198 MICROSCOPY FOR BEGINNERS. 



The bright red blood is contained in two principal 

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

 ous intestine. The upper, or dorsal one, has connected 

 with it near the anterior end of the body two little con- 

 tractile 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 ones, 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 other aquatic worms. They are 

 most conspicuous in the posterior rings, and are sup- 

 posed to represent kidneys in function. 



Tubifex is reproduced by eggs, which probably make 

 their escape after the parents' death, and after the body 

 lias fallen to pieces, as the living creature has no passage 

 for their exit. Huxley, however, says that they pass out 

 through the segmental organs the ciliated tubes just 

 referred to. 



11. NAIS (Figs. 140, 141). 



Body whitish or yellowish, 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 be- 

 ing longest. Each cluster of podal spines contains four 

 or more. The mouth is round, the front border of the 



