EARTHWORM 



235 



Pros-f'omi'unr 



xxvr- 



:xxxir- 



Opehin^ 

 oTCv/ducf 



Openm0 of 

 Is/as c/eferens 



Sem/rya/ 



one end of the animal to the other the aUmentary canal extends, a 



tube within a tube. It is held in place by the partitions, the coelomic 



spaces thus becoming ringhke. In the ventral portions of metameres 



IX to XV are the reproductive organs, while above the alimentary 



canal is the dorsal blood vessel and below 



it are the ventral blood vessel and nerve cord. 



Each metamere, except the first three and the 



last, also contains a pair of nephridia. The 



coelomic spaces are fined by a delicate epi- 



thefium known as the yeritoneum. They are 



filled with the coelomic fluid, which is colorless 



and which, when the worm contracts, can flow 



from one space to another through a small 



opening in each septum above the ventral 



nerve cord. 



271. Alimentary Canal and Metabolism. — 

 The alimentary canal is divided into a greater 

 number of regions than in any type previously 

 discussed and these are more highly special- 

 ized (Fig. 146). These regions include a buccal 

 cavity; a muscular -pharynx; a narrow esophagus; yxKVE- 

 a thin- walled ciliated crop, or proventriculus; 

 a thick-walled muscular gizzard; and a thin- 

 walled intestine, which begins at metamere XIX. 



The food of earthworms consists of organic 

 matter in the soil and of living or decaying 

 leaves: The worms will also eat bits from the 

 bodies of dead animals when they can secure 

 them. The organic matter in the soil may be 

 gathered at any time, but the fragments of 

 leaves are secured from the surface of the 

 ground at night. Taken in at the mouth by a 

 sucking action of the pharynx and mixed wdth 

 a secretion from salivary glands in the pharyn- 

 geal wall, this food is passed to the crop. 

 From here it goes into the gizzard where it is 

 ground and is then passed on into the intestine 

 where digestion and absorption take place. 

 Feces are egested at the anal opening. They appear in the form of cast- 

 ings outside the burrows. Enzymes are produced in the intestine which 

 act on proteins, fats, and carbohydrates. 



272. Circulatory System.— The circulatory system of the earthworm 

 is a compficated system of blood vessels through which the blood is 

 forced by a sort of peristaltic action of the muscle fibers in the walls of 



C//fe//a/T7 



^Sefae 



-Anus 



Fig. 144. — An earth- 

 worm, Lumhrictis terrestris 

 Linnaeus. Ventral side of 

 the more anterior and the 

 most posterior segments. 

 From a preserved specimen. 

 X 113 in length and about 

 2 in diameter. Segments 

 numbered in roman. 



