76 THE EARTHWORM. 



the ventral cord by a pair of connectives running round the 

 sides of the alimentary canal. 



1. The nerve-collar is a small ring of nervous substance 



surrounding the buccal sac just in front of the 

 pharynx, in the third segment. It consists of a pair 

 of pyriform supra-oesophageal ganglia, united by 

 their broader ends in the median plane, and sending 

 large nerves to the prostomium ; a pair of lateral 

 connectives running round the sides of the buccal 

 sac ; and a pair of closely apposed ventral ganglia, 

 the first pair of the ventral series. 



2. The ventral nerve-cord. 



Bemove the alimentary oanal, from the 'pharynx back- 

 wards, loithout 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 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 prepare these sections, kill a worm with the corrosive- 

 acetic mixture ; cut out about half an inch from the middle 

 of its length, and leave this in the mixture for four hours. 

 Wash it well, and transfer to spirit. Carefully syringe out 

 the contents of the intestine. Stain with hmmalum ; imbed; 

 and cut into transverse sections luith aynicrotome. Mount the 

 sections in order. 



Examine with low and high powers. 



