PHYLUM ANNELIDA 205 



it by passing it continually through the digestive tract. At night 

 they come to the surface of the ground, usually remaining partly 

 within or very close to the burrow, and feed on dead organic mat- 

 ter, such as leaves. Food is drawn into the mouth by suction pro- 

 duced by the muscular pharynx. In the pharynx it receives the 

 secretions from the pharyngeal glands and is then passed on 

 through the esophagus, where it receives the secretions from the 

 calciferous glands. It is then passed into the crop and is stored 

 there long enough for the secretions of the calciferous glands to 

 neutralize the organic acids which may be present in the food. It 

 is then passed into the gizzard, where it is ground by contractions 

 of the muscular walls of that organ. This process is aided by sand 

 grains which are swallowed along with the food. From the gizzard 

 the food is passed into the intestine where digestion is completed 

 and the absorption of digested materials is accomplished. 



Circulatory System 



The blood of the earthworm consists of a clear liquid plasma in 

 which there are numerous colorless cells. The red color of the blood, 

 as seen in a living specimen, is due to a pigment known as Jiemoglohin 

 suspended in the plasma and not in the corpuscles as is the case in 

 many animals. A complicated system of blood vessels makes up the 

 circulatory path of the blood. The principal ones are: (1) the 

 dorsal blood vessel, (2) the paired hearts (usually five) in segments 

 VII to XI, (3) the ventral blood vessel, (4) the subneural trunk, (5) 

 the parietal vessels, (6) the typhlosolar vessel, and (7) the intestino- 

 integumentary vessels. The dorsal vessel conveys the blood an- 

 teriorly and forces it along by waveiike contractions. The paired 

 hearts receive the blood from the dorsal vessel and by pulsating move- 

 ments force it into the ventral vessel which distributes it to the body 

 wall, the uephridia, and the intestine. In the intestine food is taken 

 up ; in the skin gaseous exchanges are made with the water in the 

 moist soil ; and in the nephridia the nitrogenous wastes are removed. 

 The lateral neural vessels receive freshly oxygenated blood from the 

 skin; hence the nervous system receives the most highly oxygenated 

 blood. From the lateral vessels it passes into the subneural, where 

 it flows posteriorly, and then returns to the dorsal vessel by way of 

 the parietal connectives. The blood flows from the intestine through 

 the typhlosole into the dorsal vessel by dorso-intestinul vessels. An- 



