TWOFOLD RESPIRATION OF ANNELIDS. GO 



another purpose, acting as an internal skeleton. You are 

 surprised at the idea of a liquid skeleton ? yet you sit on a 

 cushion of air, without the least astonishment. The fact is 

 positive : the Annelid employs its chylaqueous fluid as a 

 fulcrum by which it moves ; let the fluid out, and all power 

 of locomotion vanishes. 



The two bloods have two methods of aeration. The 

 " chylaqueous fluid" rushes into the lovely tentacles wliich 

 in many species wave above the head, and there is aerated, 

 aided by the action of the cilia which line the inner surface 

 of the tentacles. Tlie " blood" is carried to those arborescent 

 tufts, without cilia, which branch from each side of the head 

 beneath the tentacles. But although the respiratory process 

 does undoubtedly take place in these organs, yet in animals 

 so simply constructed, each organ performs more than one 

 function. Let us hear Dr Williams on the tentacles : — 



"From their extreme length, and vast number, they 

 expose an extensive aggregate surface to the agency of the 

 surrounding medium. They consist of hollow, flattened, 

 tubular filaments, furnished with strong muscular parietes. 

 Each of these hollow band-like tentacles may be rolled longi- 

 tudinally into a cylindrical form, so as to enclose a semi- 

 circular space, if they only impeifectly meet. This inimi- 

 table mechanism enables each filament to take up and firmly 

 grasp, at any point of its length, a molecule of sand, or, if 

 placed in a linear series, a row of molecules. But so perfect 

 is the disposition of the muscular fibres at the extreme end 

 of each filament, that it is gifted with the twofold power of 

 acting on the sucking and on tlie muscular principle. In 



