Phylum Annelida and Other Wormlike Coelomates 455 



in length. Often they are found in protozoan cultures in large numbers. 

 The terrestrial species or earthworms vary greatly in size. Some are 

 quite small, while others such as a species found in Australia attain a 

 length of from 8 to 10 feet. 



One of the most abundant earthworms is the European species, 

 Lmnbricus terrestris, which has been introduced into this country. It 

 is now widespread and the most abundant form in the lawns and gardens 

 about houses. 



The Anatomy of Lumbricus terrestris. — L. terrestris at times 

 attains a total length of 10 to 12 inches and is most commonly seen on 

 lawns and sidewalks after a spring rain. Its slender elongated form is 

 divided externally and internally into about 120 segments. Anteriorly 

 the worm is bluntly rounded with a ventral mouth. The mouth is in 

 segment 1, the peristomimn, with the small dorsal prostomium just an- 

 terior. In segments 31 to 37 is a glandular swelling forming a dorsal 

 saddle, the clitellum, which secretes the material forming the egg capsule. 

 In the last segment of the worms is the anus. Each segment except for 

 the first and the last has four pairs of small setae. 



Besides the mouth and anus there are a number of other smaller 

 openings (Fig. 150,^). On every segment but the first three and last, 

 there is a pair of small lateral-ventral openings, the nephridiopores. Ex- 

 cept for the first eight segments, each has a small dorsal opening, the 

 dorsal pore. This pore is located at the anterior dorsal portion of the 

 segment and communicates directly with the coelom. In the furrows be- 

 tween segments 9 and 10, and 10 and 11 are the tiny paired openings of 

 the seminal receptacles. These are laterally placed. On segment 14 are 

 the ventral openings of the paired oviducts. Ventrally on segment 15 are 

 the openings of the paired sperm ducts. Around these latter openings 

 are swollen lips from which ridges extend to the clitellum. 



In typical annelid fashion, a cross section demonstrates the "tube 

 within a tube" construction of the body. The cuticle, the glandular 

 epidermis, the circular and longitudinal muscle layers, and the parietal 

 peritoneum form the body wall. In the regions where the setae emerge, 

 special retractor and protractor muscles are visible. The coelom is 

 divided into segments by the septa and portions of the coiled nephridia 

 may be seen in each segment. The entire digestive tract is maintained 

 in its central position by these septa. 



Anteriorly the mouth opens into the buccal cavity which occupies 

 the first three segments and which leads into the muscular pharynx of 



