The Earthworm. 21 



thinner and less curved. The clitellum, to which reference 

 has been made, is a region of the body which stands out 

 conspicuously by reason of its glandular, smooth, and swollen 

 appearance. It occupies a variable number of segments, 

 and commences at a variable segment, the variability corre- 

 sponding with different species. It never, however, com- 

 mences further forward than the twenty-third or twenty-fourth 

 segment. The clitellum is sometimes termed the cingulum or 

 the girdle. At the commencement of the clitellum there are 

 . on the ventral surface of the body certain glandular eminences, 

 more conspicuous in immature worms in which the clitellum is 

 not yet formed. These, again, vary in number and position 

 according to the species, and are known as the tubercicla 

 pubertatis. 



If an earthworm be dried with blotting-paper and then 

 gently squeezed, liquid will be seen to exude or even to spirt 

 out from certain pores placed along the back. These are the 

 dorsal pores, and lie in the middle line of the back between 

 successive segments. They do not begin for some distance 

 behind the anterior extremity, and the exact segment at which 

 they do commence is another of those points which varies with 

 the species. A careful examination, especially of spirit- 

 preserved examples, shows a second series of pores, which, 

 unlike the dorsal pores, are paired, a pair to each segment. 

 These lie laterally, and are placed in front of the more ventral 

 couple of setae. Their position, again, varies somewhat in some 

 species, and they are not apparent on the first two or three 

 segments of the body. These pores are termed the nephridio- 

 pores ; they are the openings of the excretory organs. 



On the fifteenth segment of the body are a pair of very 

 conspicuous orifices with tumid lips, lying iDetween the dorsal 

 and the ventral pair of setae. These orifices are those of the 

 sperm ducts, but in some species they are not so obvious as in 

 others. On the segment in front of this — i.e. the fourteenth 

 — are two other orifices very minute and not always easy to 

 see, the oviducal pores. Less easy, again, to see are a series of 

 pairs of orifices not fewer than two pairs, lying generally 

 between segments 9 and 10 and 10 and 11. These are the 



