LUMBRICUS 



143 



alimentary canal which push it along ; on its passage it is mixed 

 with the secretions of the calciferous glands. It has been sug- 

 gested that since the decaying vegetation on which the worm feeds 

 is strongly acid in character the calcareous particles secreted by the 

 calciferous glands tend to neutralise these acids. The crop serves 

 as a resting-place in which the food accumulates before passing into 

 the gizzard. The hard, horny walls of the last-named chamber help 

 to grind up the food and render it fit for the action of the juices 

 which digest it. The process of digestion, or the rendering of the 

 food soluble, probably takes place in the intestine, and through the 

 walls of this portion of the alimentary canal the soluble products of 



FIG. 61. Six segments from the intestinal region of an Earthworm, Lumbricua 

 tcrrestris, dissected to show arrangement of parts. Magnified. From 

 Hatschek and Cori. 



1. Septa. 2. Nephridia. 3. Ventral nerve-cord. 4. Sub-neural 

 blood-vessel. 5. Nephrostomes, internal funnel-shaped openings of 

 nephridia. 6. Intestine. 7. Typhlosole. 8. Circular blood-vessels. 

 9. Ventral or sub-intestinal blood-vessel. 10. Dorsal blood-vessel. 



digestion soak, and are taken all over the body by the blood-vessels 

 and probably also to some extent by the fluid in the coelom. 



The series of contractions which squeeze the food onwards 

 towards the anus are known as peristalsis; they constitute the 

 sole movements of which the alimentary canal is capable and are 

 carried out by muscles developed from the cells of the inner wall 

 of the coelom, which pass round the canal like a series of rings 

 or tight india-rubber bands. 



The earthworm eats earth and manages to find sufficient 

 nourishment for its needs in the small amount of organic matter, 



