ANNULATA (RING-WORMS) 



143 



The head segment consists of two distinct portions, — the 

 anterior of which bears dorsally four simple eyes and anteriorly 

 a pair of slender tentacles or feelers and a pair of thick palps ; 



Fig. 55. — The common carnivorous worm, Nereis virens from Massachusetts Bay. 

 A, entire worm. B, a paddle (or parapodium, — much enlarged) from the fifty- 

 fifth segment. C, the head of another specimen, showing the toothed jaws ex- 

 tended, an., anus; e., eyes; j., jaws; p., palp; par., parapodium; seg., seg- 

 ments or divisions of body ; /., tentacles ; /./., terminal feelers. (A and C X f .) 



the posterior portion bears antero-laterally four pairs of tenta- 

 cles. The tail segment bears merely a pair of long terminal 

 feelers. The body is inclosed in a very thin layer of chitin 

 secreted by the epidermis beneath it. 



Beneath the epidermis are circular muscles by which the 

 worm can diminish its diameter, while beneath these are four 

 longitudinal muscles which can diminish its length; the latter 

 are arranged in two pairs, a dorso-lateral and a ventro-lateral 

 pair. Besides these there are muscles to move the parapodia. 



Its food consists of both plants and animals, but especially 

 the latter. It is active and voracious, eating especially crus- 

 taceans and other worms. At night it leaves its burrow, swim- 

 ming actively about in search of food, at which time many of 

 these worms are eaten by fishes. The mouth is situated at 

 the end of the head upon the under side ; through this Nereis 

 can thrust out the anterior portion of its oesophagus, by a process 

 of rolling inside out as with the finger of a glove. This thrust- 

 out portion, the proboscis, is provided with two laterally placed, 



