10 EARTHWORMS AND LEECHES [CH. I 



liquid itself; and, speaking generally, it is the case that 

 such oxygen-carriers are found either in animals whose 

 bulk is considerable in proportion to their respiratory 

 surfaces, or in animals which though small live in an 

 environment poor in oxygen, e.g. Tubifex living in mud, 

 and the aquatic larvae of some species of Chironomus 

 (Gnat). It is very probable that the worms so often 

 seen on the surface of the ground after heavy rain have 

 come up to avoid the suffocation to which they assuredly 

 are exposed when the soil becomes saturated and much 

 of the included air expelled by the water. Many worms, 

 however, normally live in very moist places and can with- 

 stand prolonged immersion in water. In order to test 

 their powers of endurance in the absence of oxygen I 

 placed one worm in a flask full of water that had been 

 boiled to expel all gases and then allowed to cool in an 

 atmosphere of carbon dioxide: in 3 minutes the worm 

 was asphyxiated and to all appearance dead. A second 

 worm was placed in ordinary tap-water that had not been 

 boiled and though it made strenuous efforts to get out it 

 was still alive and vigorous after 1J hours' immersion; on 

 transferring it to the other flask it too in a couple of minutes 

 lay motionless. I then poured off the water and filled the 

 flask with oxygen gas : the second worm recovered in ten 

 minutes, and the first, which had been drowned for nearly 

 1 j hours, in about double that time. 



Excretion. The chief excretory organs of the body are 

 the nephridia. These are fine, much convoluted tubes, 

 opening internally by ciliated funnel-shaped mouths into 

 the body-cavity and externally on the ventral surface. 



