170 SEGMENTED WORMS— THE ANNELIDS 



burrows in the ground and crawl around on the surface on damp nights. 

 If you will take a flashlight and go out on the campus some dark night 

 about midnight when it is pouring rain you may see some earthworms 

 crawling around on the surface. It is a little more convenient and con- 

 siderably drier to wait until the next morning and then see some of them 

 on the surface that failed to get under before the sun came up and suffo- 

 cated as their skins dried. Normally, when the rain stops and the air 

 becomes a little dry, the worms will crawl back in the ground by eating 

 their way down. Those which succeed leave little castings of dirt on 

 the surface as evidence of their prowling, while those that find them- 

 selves on a concrete walk are likely to have considerable difficulty trying 

 to eat a hole through it to get in the ground beneath. Their dead bodies 

 can be seen on the walks as an evidence of their unfortunate predicament. 



It might be difficult to convince a golfer that earthworms are such 

 nice and beneficial creatures after his ball has been deflected from the 

 hole by earthworm castings on the green, and many golf courses put 

 poison in the ground to prevent such an occurrence that may loom as 

 catastrophe at the moment. 



Lumbricus has the best developed digestive system that has been 

 studied. Some of its nourishment comes from the digestion and absorp- 

 tion of the decaying organic matter that is present in the soil which the 

 worm eats as it moves about. However, it has another and more efficient 

 method. The mouth is at the anterior end and bits of leaves or other 

 food may be ingested with the aid of the pharynx which is next in line. 

 The pharynx is muscular in nature and capable of expansion and con- 

 traction, so the earthworm places its mouth over the food and the 

 pharynx suddenly expands, thus creating a suction that pulls the food in. 

 This is not such a strange method of ingestion since many people use the 

 same principle in getting soup into their mouths. The food is then 

 forced from the pharynx and down the esophagus by rhythmic contrac- 

 tions of the walls which are called peristaltic movements. These same 

 movements are found in the human alimentary tract and are involuntary 

 in nature. Once a mouthful of food reaches your pharynx, or throat, it 

 is seized by these contractions and carried on down your esophagus to 

 your stomach even though you may change your mind and decide that 

 you do not want to swallow it. The earthworm empties the food into 

 the crop, which is a storage chamber from which the food is released in 

 small portions to the gizzard. Birds and earthworms have something 

 in common ; neither of them have teeth and both of them have a crop 

 and a gizzard. The gizzard makes up for the lack of teeth by grinding 

 the food which was swallowed whole at the mouth. Sand grains are in 

 the gizzard of the earthworm to aid in the grinding process, and birds eat 



