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CHAPTER XIII. 



ANNELIDA.* Red-blooded Worms. (Cuv.) 



(231.) The lowest class of articulated animals comprehends an ex- 

 tensive series of creatures generally grouped together under the com- 

 mon name of Worms. In the outward form of their bodies many 

 of them resemble some of the more perfect Entozoa, and we need 

 not therefore be surprised that in ordinary language they are not 

 unfrequently confounded together. But whatever may be the 

 similarity in outward appearance between the more perfect intes- 

 tinal worms, and the animals belonging to the class upon the con- 

 sideration of which we are now entering, the examination of their 

 anatomical structure will at once show that they differ widely from 

 each other, and have thus been properly separated by a consi- 

 derable interval in all the more modern systems of zoological 

 arrangement. 



(232.) The principal characters which serve to distinguish the 

 Annelida from other forms of the animal world are readily appre- 

 ciated ; and, when once pointed out, will be found sufficient for the 

 guidance of the most superficial observer. The body is always 

 considerably elongated, and composed of a succession of rings or 

 segments, which, with the exception of the first and last, scarcely 

 differ from each other except in size. Each ring is generally 

 found to be furnished with a set of short spines or setae, calcu- 

 lated to assist in locomotion ; but in no instance are these animals 

 provided with articulated legs. The first segment of the body, 

 which may be called the head, contains the mouth, sometimes 

 provided with a formidable apparatus of jaws ; and is also generally 

 furnished with eyes, and variously shaped tentacula, which are 

 apparently instruments of touch. The last segment also, which 

 is generally the smallest, occasionally presents setiform appen- 

 dages, and occasionally a prehensile sucker, used as an organ of 

 progression. 



Their blood is remarkable for its red colour, and circulates 

 in a double system of arteries and veins ; respiration is effected 

 either in membranous sacculi contained within the body, or by 

 means of arborescent tufts appended to various parts of their ex- 



* Annellus, a little ring. 



