60 ANIMAL FORMS 
form along almost any seashore. The body presents the 
same segmented appearance as the earthworm, but the 
head (Fig. 37, A) is provided with numerous sense organs, 
chief among which are four eyes and 
several tentacles or “ feelers.” 
The segments behind the head 
Fia. 37.—A, head and one of the lateral appendages (B) of a marine worm (Nereis 
branadtii); al, intestine ; f, ‘‘ gill” ; %, kidney ; m, nerve cord ; s, bristles for loco- 
motion. 
differ very little from one another, and, unlike those of 
the earthworm, each bears a pair of lateral plates (Figs. 
36, 37, B) or paddles with many lobes, some of which bear 
numerous bristles. By a to-and-fro movement these organs 
aid in pushing the animal about, or may enable certain spe- 
cies to swim with considerable rapidity. 
As in all other worms, respiration takes place through 
the surface of the body, the area of which is increased by 
the development, on certain portions of the paddles (para- 
podia), of plates penetrated with numerous blood-vessels, 
which thus become special respiratory organs or gills 
(Fig. 37, B). 
In their internal organization the Polychetes are con- 
structed practically on the same plan as the earthworms, 
the principal difference being in the reproductive system. 
In the earthworm this is restricted to some of the forward 
segments, while in the present group the eggs and sperms 
