THE EARTHWORM 



169 



bottom of the sea. Perhaps the commonest burrowers, how- 

 ever, are those elongated animals — elongated in association 

 with the iDurrowing capacity — that we call sea-worms. A 

 fuller account of many of them is given in another chapter. 

 Many of the Crustacea burrow and feed upon the burrowing 

 worms. 



The burrowers of the land are the best known to us. They 

 have been derived from organisms that lived in fresh water. 



Fig. 162. — Flash-light photograph of earthwomi and wlug crawling on a 

 pavement at night. Photo, by D. and S. 



Among the land burrowers are the earthworms; certain 

 Crustacea, like the crayfish ; many insect larvae ; and a few 

 mollusks and vertebrates. In the present chapter we have 

 especially to consider the earthworm (Oliogochata ')• 



Earthworms, as the name implies, are inhabitants of the 

 ground, through which they burrow and in which they gain 

 their food. They sometimes come to the surface at night in 

 search of companions and food (Fig. 162). Even during the 

 day in rain}' weather they extend the anterior end of the bodj' 

 out of their burrows. Earthworms, found on the surface at 

 other times, have, for the most part, been parasitized by a 



' oligos, few ; chcete, hair. 



