THE EARTHWORM. 13 



worm-shaped masses, well known to gardeners and 

 others as " worm-castings." Of these more hereafter. 



The digestive apparatus is of the simplest kind, 

 consisting of a straight alimentary canal which runs 

 from one end of the body to the other, commencing 

 at the mouth and terminating in the final posterior 

 ring. This tubular stomach is slightly constricted at 

 each ring, and is covered externally along its whole 

 length with a granular envelope, composed of nu- 

 merous glands, which secrete a fluid that aids in the 

 digestion of the ahmentary substances and their 

 elaboration into the blood (PL II. fig. 4, section of 

 Worm's body, showing the form of alimentary canal) . 



If you examine the living worm, you will notice a 

 fine crimson streak shining through its semitrans- 

 parent covering j this is the main trunk or artery 

 which extends along the whole body, in the same 

 manner as the alimentary canal, and serves as the 

 receptacle of the blood. To observe the circulation 

 of the latter, you need but remove a worm from the 

 ground, and keep it a little while, until it has voided 

 the earth which it contained, and thus rendered its 

 body more transparent ; you will then be able to distin- 

 guish the crimson current as it courses along the crea- 

 ture's back, flowing from the tail to the head confined 

 within the central artery ; and on turning it upon its 

 back you will perceive the return current flowing in the 

 opposite direction, through another blood-vessel, situ- 

 ated near the abdominal surface. The dorsal vessel 

 must be regarded as the heart, and partakes to some 



