288 



ANIMAL SKETCHES. 



CHAP. 



more cruel than to choke water-breathing organisms by 

 inches, through carelessness in not keeping the water 

 pure. And we must remember that water, like air, may 

 be quite clear and bright-looking, and yet be utterly unfit 

 to breathe. Of course, if you have green water- weeds 

 growing in a well-lit tank, these will serve to keep the 

 water sufficiently supplied with oxygen ; but failing this, 

 change the water often. 



You will notice, as your crayfish moves about at ease in 

 the basin, that he walks on eight pairs of legs, of which 



CRAYFISH. 



the first two pairs bear small pincers at the tips, while the 

 others end in points. There is nothing like a flattened 

 foot. And the crayfish is so light under water that he 

 seems barely to touch the surface on which he walks. In 

 front of the legs are the great pincer claws with which he 

 can give you a pretty smart nip if you give him a chance. 

 These are generally carried, unless the animal is disturbed, 

 with their tips just resting on the bottom. Very con- 



