CHAP. I. THEIR STRUCTURE. 17 



consists of from 100 to 200 almost cylindrical 

 rings or segments, each furnished with minute 

 bristles. The muscular system is well 

 developed. Worms can crawl backwards as 

 well as forwards, and by the aid of their 

 affixed tails can retreat with extraordinary 

 rapidity into their burrows. The mouth is 

 situated at the anterior end of the body, and 

 is provided with a little projection (lobe or lip, 

 as it has been variously called) which is used 

 for prehension. Internally, behind the mouth, 

 there is a strong pharynx, shown in the ac- 

 .companying diagram (Fig. 1) which is pushed 

 forwards when the animal eats, and this part 

 corresponds, according to Perrier, with the pro- 

 trudable trunk or proboscis of other annelids. 

 The pharynx leads into the oesophagus, on 

 each side of which in the lower part there 

 are three pairs of large glands, which secrete 

 a surprising amount of carbonate of lime. 

 These calciferous glands are highly remark- 

 able, for nothing like them is known in any 

 other animal. Their use will be discussed 

 when we treat of the digestive process. In 

 most of the species, the oesophagus is enlarged 

 into a crop in front of the gizzard. This 



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