72 THE EARTHWORM 



The chain 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 OF THE 

 INTESTINAL REGION. 



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 ^re^are these sections hill a worm with cold saturated 

 solution of corrosive sublimate ; cut out about half an inch 

 from the middle of its length, and leave this in the sublimate 

 for twenty-four hours. Wash it well, and transfer to spirit. 

 Ga/refully syringe out the contents of the intestine. Stain; 

 imbed, and cut into transverse sections with a microtome. 

 Mount the sections in order. 



Examine with low and high powers. 



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. 



2. The epidermis lies immediately below the cuticle. It 



consists of a single layer of columnar cells, set side 

 by side at right angles to the surface, with nuclei 

 near their bases. Many of these cells have the 

 character of ' goblet cells,' being distended by a 

 granular secretion formed within them ; other cells 



