94 Descriptive Zoology. 



the typhlosole. It is richly supplied with blood tubes and 

 serves to increase the surface for the absorption of food. 



As the food passes along the digestive tube it has added 

 to it liquids secreted by the intestinal walls, and these 

 juices have the power to digest starchy, fatty, and proteid 

 foods. As the food is digested it is absorbed through the 

 intestinal walls, either into the liquid of the body cavity, 

 or into the blood tubes that branch through the walls of the 

 intestine, or into both of these. 



The Blood. The blood of the earthworm is red, and the , 

 red color is due to a substance called hemoglobin, as in 

 human blood. But the color is in the liquid itself, and not 

 in the corpuscles as in our blood. Small colorless corpus- 

 cles are present in the blood. The liquid found in the 

 body cavity has also corpuscles, and this liquid is compara- 

 ble to the lymph of higher animals. It is colorless or 

 sometimes milky in appearance. There is a minute pore 

 opening in the dorsal part of most of the segments. 



Circulation of the Blood. In watching the live earth- 

 worm one sees a dark red streak through the dorsal wall ; 

 this is the dorsai blood tube. It usually shows plainly a 

 wavelike motion running from the posterior end to the 

 anterior end. The action is due to the successive short- 

 ening of the circular muscle fibers in the wall of the 

 blood tube, from behind forward. This sort of action is 

 familiar to many under the name of peristaltic action, 

 such as takes place in the intestines of most animals. By 

 this action the blood is continually driven forward in this 

 blood tube. A similar blood tube is to be found under 

 the intestine, the ventral blood tube. In it, by the same 

 means, the blood is sent backward. These are the princi- 

 pal longitudinal blood tubes, but there are three small 

 tubes close to the nerve cord. In the region of the gullet 



