146 



INTRODUCTION To ZOOLOCJY. 



ments 13-16; tlie gizzard, in segnieiits IT-'^O; the 

 intestine, the rest of the way. 



h. In the iloor of tlie Ijody cavity, note the nerve 

 cord and ganglia. 



Cross S<Mtion. 



1. Tlie cuticle has already 

 section shows the outer layer ci 



CR ss ^1 11 



I I VK I IIW [ M 



a cutiflp /' (iiculii iiuisi 1p c 1)11- 

 gitudinal iiiusc le (/ ddisil l)l(«i(l\ essel ; 

 f, aliineiit<ii> ( xnal / ^et f c \eiiti il 

 nei%e coiil, h, ^eiitial blood ^ esbel , /, 

 repioduotive organs. 



the ground, and so furnish 



leen seen. The cross 

 muscles. This layer 

 is circular, and runs 

 around the body. 

 AVhen it contracts, 

 it tends to diminish 

 the diameter (jf the 

 ])ody ; 1)11 1 l)y the 

 tliminution in diam- 

 eter, the length be- 

 comes greater, and 

 the distance be- 

 tween the head and 

 tail is increased. If 

 tlie sct^e point back- 

 ward, as they ordi- 

 narily do, the in- 

 crease in distance 

 between the h e a d 

 and tail will drive 

 the setie at the pos- 

 t e rio ]• part of the 

 111 anchor 



body into 



which prevents the tail f'i'om moving backward; 

 hence, lengthening th(j liody pushes the head forward. 

 When the head is pushed forward, the backward 

 pninting set;c slip freely over the surface. Thus there 

 is a forward moTement of the head, and no liaekward 

 movement of the tail. 



'/!. Tlie cross section shows also a layer of muscles in- 

 side the circidai' la}'er. This is a layei' of longitudinal 



