ANNELIDA 



89 



The sea- worms here mentioned are only a few representa- 

 tives of the many to be found on our coasts. They have been 

 chosen because they illustrate in some degree the variety of 

 structure found amongst the Chaetopod worms, and their 

 powers of adaptation to different spheres of life. Earthworms 

 are more or less protected by their underground habit, and, 

 since air is plentiful in their burrows and their skin is so thin 

 as to be penetrable to it, they have no need of special respira- 

 tory organs. Sea-worms on the other hand, living exposed 

 to the attacks of many enemies and being in many cases 

 sedentary, need a protective tube, and this necessitates special 



FIG. 45. Spirorbis borealis. 

 A, Attached to seaweed (nat. size). B, One individual much enlarged. 



respiratory gills which they can project beyond the tube, and 

 in which the blood is oxygenated. 



We are not accustomed perhaps to think of worms as 

 things of beauty, and yet these sea-forms exhibit some of the 

 most wonderful colours seen in the animal kingdom, and the 

 study of them well repays both the artist and the naturalist. 



Class II. : H1RUDINEA OR LEECHES 

 (RINGED WORMS DESTITUTE OF BRISTLES) 



Leeches are usually water-inhabiting creatures though 

 they are found also in damp earth. They swim through the 



