ANNELIDA. 197 



The skin on the surface of the earth-worm is furnished 

 at the parts where it covers the rings, witli very minute bris- 

 tles, called Setx, by means of which the animal is enabled 

 to fix those parts on the ground, while the other portions of its 

 body are in motion. Both in the anterior and posterior seg- 

 ments, these hairs are directed towards the centre of the ani- 

 mal; while those on the middle segments are perpendicular.* 

 We almost constantly find, in animals belonging to the or- 

 der of Annelida, some provision of this kind. Often it con- 

 sists of tufts of hair regularly disposed in rows on each side 

 of the under surface. In the Nei^eis (Fig. 129,) a genus of 

 sea-worms, there are often above a hundred pair of little tufts 

 of strong bristles: and between these we find tentacula to pre- 

 vent the animal from running against any thing by which it 

 might be injured. They also raise the body from the ground; 

 for which purpose, as they are used under water, very little 

 support is necessary.! Sometimes the whole body is covered 

 with hair; at other times these appendages are in the form 

 of hooks, which, of course, give greater power of clinging to 

 the objects on which they fasten. In some, again, they as- 

 sume more the nature of feet, of which they exercise durinc; 

 progression all the functions; being furnished with several, 

 sets of muscles for adjusting and strengthening their actions. 

 The mode by which an animal of this description advances 

 along the ground is very simple. It first protrudes the 

 head by the elongation of the foremost segments of the body, 

 while the others cling to the earth by means of tlie rings, 

 and also of the bristles and other appendages to the integu- 

 ments. The head is then applied to the ground, and made 

 the fixed point, and the segments next to it, which had been 

 elongated, are now contracted by the action of tiicir longi- 

 tudinal muscles; in doing which, equal portions of tlie suc- 



* As an instance of the extraordinary multiplicity of species existing in 

 every department of living- nature, I may here notice, that of the common 

 earth-worm, ajiparcntly so uniform in its shape, Savig-ny has lately, by a 

 closer examination, been able to disting-uish no less than twenty-two diflercnt 

 species amoni^ those found in the neighbourhood of Paris alone. 



f Home; Lectures, &c. Vol i. p. 115. 



