Phylum Annelida and Other Wormlike Coelomates 



451 



anteriorly a pair of small tentacles. All segments except the peri- 

 stomium and the last anal segment bear parapodia. The last segment 

 contains the anal opening and a pair of cirri. 



Each parapodium (Fig. 145,5) consists of a dorsal lobe, the noto- 

 podium, and a ventral lobe, the neuropodium. Each lobe contains 

 numerous setae and a projection known as the cirrus. Inside the in- 

 dividual parapodium are two chitinized rods, the aciculi, which support 

 it and aid in movements. Capillaries are present in the individual para- 

 podium ; thus the parapodia perform the double function of respiration 

 and locomotion. 



PERISTOMIAI. 

 TENTACLES 



PERISTOMIUM 



DORSAL CIRRUS 



NEunOPODIUU 



VENTRAL CIRRUS. 



Fig. 145. — The clamworm, Neanthes. A, Anterior end; B, a 

 parapodium; C, trochophore larva. 



In cross section, the body of Neanthes is shown to be of a tube 

 within a tube construction. The outer tube is the body wall, the inner 

 one the digestive tract. A number of layers form the body wall. The 

 outermost of these is the thin, noncellular cuticle. Directly below this 

 is the single-celled epidermis which contains numerous glands. Part 

 of the dorsal epidermis is well supplied with blood vessels and may 

 assist the parapodia in gaseous exchange. Internal to the epidermis 



