84 THE EARTHWORM. 



2. The ventral nerve-cord. 



Remove the alimentary canal, from the pharynx back- 

 wards, without injuring the nerve-collar and ventral cord. 



The cord runs along the ventral body-wall in 

 the middle line, giving off three pairs of nerves in 

 each segment along nearly the whole length of the 

 body. The cord is slightly swollen opposite the 

 middle of the segments, the swellings or ganglia 

 being more conspicuous in the hinder part of the 

 body. 



III. EXAMINATION OF TRANSVERSE SECTIONS. 



The structure of the body-wall and alimentary canal, and 

 many other points in the anatomy of the earthworm, are best 

 understood from a microscopical examination of transverse 

 sections of the whole animal. 



To prepare these sections, take a worm which has thoroughly 

 evacuated its food contents and kill with the corrosive-acetic 

 mixture ; cut out about half an inch from the (esophageal region 

 and also from the middle, and leave these in 70 per cent, spirit 

 with trace of iodine added. Stain with hcemalum ; imbed ; 

 and cut into transverse sections with a microtome. Mount the 

 sections in order. 



Intestinal Region. 



A. Shape. 



The section is nearly circular in outline. The dorsal 

 surface is indicated by the typhlosole, the ventral by the 

 nerve-cord. 



B. The Integument. 



1. The cuticle is a thin structureless superficial layer, often 

 separated by the action of the reagents from the 

 underlying epidermis. 



