304 ANNELIDA 



Oligochasts are poorly provided with special sense organs. Pig- 

 ment eyes are present in certain naids; tactile cells and processes may 

 be present but tentacles never are. The forward part of the body of 

 earthworms is especially sensitive to light and other stimuli. 



The terrestrial oligochaets are the earthworms. These familiar ani- 

 mals are often of large size, the largest being six feet in length, and 

 are found in temperate and tropical countries in all parts of the world. 

 They are nocturnal animals which live in burrows in the soil and feed 

 on decaying vegetation and the organic particles in the soil, which they 

 pass in large quantities through the intestine. Darwin has estimated 

 that an acre of ordinary ground will have about 63,000 earthworms 

 which bring many tons of earth to the surface from a foot or two 

 beneath. They are thus important agents in renewing the surface soil. 

 The aquatic oligochasts live mostly at the bottom of fresh-water 

 streams and ponds, although a few live in the sea, often in tubes of 

 mud or sand, and eat aquatic vegetation. The order contains over 1,200 

 species and about 11 families. 



Key to the families of Oligochceta here described: 



! Worms microscopic 1. ^EOLOSOMATIDAE 



c 2 Worms not microscopic. 



&! Parasitic worms with terminal sucker 2. DISCODRILIDAE 



6 2 No sucker present. 



c x Worms very long and filiform 3. HAPLOTAXIDAE 



C 2 Worms not so formed. 



d l Worms usually very small and slender and mostly aquatic. 

 d Reproduction mostly by serial budding, animal chains being formed. 



5. NAIDIDAE 



e 2 Such reproduction not present, or at least uncommon. 

 /! Spermatheca far forward, usually opening in segment 4 or 5. 

 / 2 Spermatheca farther back. 4 - ENCHYTB^IDAE 



0! Setae usually more than 2 in a bundle and usually of more than 



one form 6. TUBIFICIDAE 



g z Setae paired and all of one form 7. LUMBRICULIDAE 



d 2 Worms large and mostly terrestrial ; earthworms. 

 Ci Clitellum begins before segment 18 and contains the male pores. 

 /! Male pores in hinder margin of clitellum or entirely behind it. 



8. MEGASCOLICIDAE 



/ 2 Male pores in forward portion of clitellum 9. GEOSCOLECIDAE 



e a Clitellum begins at or behind segment 18 ; male pores some distance 



in front of it 10. LUMBBICIDAE 



396, 1895. "Notes on Species," etc., by same, same jour., Vol. 5, p. 441, 1900. "Notes 

 on Species of N. A. Oligochaeta, IV," by same, same jour., Vol. 5, p. 459, 1900. 

 "Oligochaeta," by W. Michaelsen, Das Tierreich, 1900. "Researches in American 

 Oligochaeta," etc., by G. Eisen, Proc. Cal. Acad. Sci., 3d Ser., Zool., Vol. 2, 1900. 

 "Hirudinea and Oligochaeta Collected in the Great Lake Region," by J. P. Moore, 

 Bull. U. S. Fish. Com., Vol. 25, p. 155, 1905. "Some Marine Oligochaeta of New 

 England," by J. P. Moore, Proc. A. N. S., Phila., 1905, p. 373. "Die Susswasserfauna 

 Deutschlands," Heft 13, "Oligochseta," by W. Michaelsen, 1909. "The Common 

 Freshwater Oligochaeta of the United States," by T. W. Galloway, Trans. Am. Mic. 

 Soc., Vol. 30, p. 285, 1911. 



