EARTHWORMS, LEECHES, ETC. 101 



This is an arrangement that we find common in all the higher 

 animals. 



In the alimentary canal a number of distinct parts may be 

 recognized. Anteriorly is the muscular pharynx, which is 

 followed by a narrow esophagus leading directly into the 

 thin-walled crop; next comes the muscular gizzard, and next 

 the intestine, which opens externally in the terminal segment 

 through the anus. The anterior end of the alimentary canal 

 is more or less protrusible, while the posterior portion is held 

 more firmly in place by the septa, which act as mesenteries. 

 Surrounding the narrow esophagus are the reproductive organs, 

 three pairs of large white bodies and two pairs of smaller sacs. 

 Under the reproductive organs are three pairs of bag-like 

 structures projecting from the esophagus. The front pair 

 are the esophageal pouches; the next two pairs are the esopha- 

 geal, or calcijerous, glands. They communicate with the 

 alimentary canal, and secrete a milky calcareous fluid. 



By cutting transversely through the alimentary canal in the 

 region of the clitellum, a dorsal fold of the intestine, the 

 typhlosole, may be seen extending into the lumen. This fold 

 gives a greater surface for digestion, and in it are a great 

 many hepatic or special digestive cells. The entire alimentary 

 canal is lined internally with epithelium. 



The dorsal blood-vessel lies along the dorsal surface of the 

 alimentary canal. From the anterior portion there arise 

 several circumesophageal rings, or " hearts." These hearts 

 are contractile, and serve to keep the blood in motion through 

 the blood-vessels. Just beneath the alimentary canal is the 

 ventral blood-vessel, and still beneath this the ventral nerve-cord. 

 The slight swellings on the nerve-cord in each segment of the 

 body are the ganglia. The brain, or cerebral ganglion, lies in 

 the first segment of the body above the esophagus, and is con- 

 nected with the ventral nerve chain by the circumesophageal 

 collar. 



The excretory system is peculiar, consisting of a series of small 

 convoluted tubes, the inner ends of which are furnished with 

 small ciliated funnels which gather and carry off the waste 

 matter from the fluid that fills the body-cavity. There are 



