CHAPTER II 

 ANNELIDA 



A POLYCHAETOUS ANNELID {Nereis virens) 



Nereis is a common marine worm which lives in the sand 

 along the shores of our northern and middle states. Its food con- 

 sists of various kinds of small marine animals, which it catches 

 with its formidable, protrusile proboscis. A specimen should 

 be selected for study in which the proboscis is not thrust out. 



Observe, in the first place, the long, segmented, and some- 

 what flattened body, the pair of appendages on each segment, 

 and the distinct head with special sense-organs at the forward 

 end ; observe also that the body tapers towards the hinder end, 

 where is a pair of special sense-organs, the long caudal feelers. 

 All of these characters indicate an animal possessed of the power 

 of rapid locomotion. Count the somites or body-segments ; note 

 that they are almost exactly alike. This lack of specialization 

 is in sharp contrast to the condition of the somites in most arthro- 

 pods. Observe carefully the appendages ; they differ from those 

 of the arthropod in that each one is an unjointed expansion of 

 the body-wall, whereas the arthropodous appendage is segmented. 

 Each one is made up of several lobes and is provided with long 

 bristles or setae. Note the absence of a hard shell, the external 

 integumentary covering being the glistening cuticula, which 

 has not been stiffened by the presence of calcareous salts. 



Observe the head and the forward portion of the body. 

 An annelid's body is composed genetically of two portions: 



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