Phylum Annelida and Other Wormlike Coelomates 457 



These latter glands contain particles of calicum which are secreted into 

 the esophagus. Behind the thin-walled crop is the heavy muscular gizz- 

 ard (segments 17 and 18) which leads directly into the long stomach- 

 intestine. This latter terminates in the anus which is located in the pos- 

 teriormost segment of the body. 



EPIOCRMIS 



LONGITUDINAL 

 MUSCLE 



CHlOfUGOCEN 

 CELLS 



NEPHRIDIUM 



VENTRAL SLOOO 

 VESSEL 



LATERAL NEURAL 

 BLOOO VESSEL 



SETA MUSCLES 



.VENTRAL NERVE 



cono 



SUBNeuBAL 



BLOOD VESSEL 



Fig. 148. — Cross section of the earthworm, Lumbricus, posterior to the clitellum. 



A cross section (Fig. 148) of the stomach-intestine shows that the 

 digestive tract is composed of a number of layers. The lumen is lined 

 with a thin cuticle. Directly beneath this cuticle is a layer of tall, ciliated 

 columnar epithelial cells, some of which are enlarged into unicellular 

 glands, and others which are specialized for absorption of digested foods. 

 Extending into the lumen at the dorsal portion is the typhlosole which 

 is also covered with the intestinal epithelium. This structure is a longi- 

 tudinal fold, running the length of the stomach-intestine ; it functions to 

 increase the digestive surface. External to the digestive epithelium is a 

 thin layer of connective tissue overlain by the muscular layers. There is 

 an internal circular layer and an external longitudinal one. In the stom- 

 ach-intestine, these layers are quite thin and difficult to distinguish while 

 in the pharynx they are much heavier. Surrounding the intestine is a 

 mass of loose yellowish cells, the chloragogen cells. These also fill the 

 typhlosole. The function of these cells is not clear, but it has been sug- 

 gested that they may have a nutritive function for the developing eggs 

 or that they may be excretory. 



The blood of the earthworm circulates through a complex series 

 of closed tubes (Fig. 149). Of these, the dorsal blood vessel is largest 

 and is present just dorsal to the digestive tract. It is connected with 



