OLIGOCH^TA 



303 



FAMILY HEEMELLIDAE. 



With the characters of the suborder : 3 genera. 



SABELLARIA Lamarck. With the characters of the suborder: sev- 

 eral species, 1 at Woods Hole. 



S. vulgaris Venill. Color yellowish or reddish ; length 3 cm. ; width 

 2.5 mm.: North Carolina to Cape Cod; from low-water mark to 10 

 fathoms; common in tubes of sand, also on shells. 



ORDER 2. OLIGOCKETA.* 



Mostly fresh-water or terrestrial, 

 hermaphroditic annelids which are with- 

 out parapodia and cephalic appendages 

 (Fig. 478). The setae are few in num- 

 ber and project from pits in the body 

 wall; in the Discodrilidae and Anachceta 

 they are wanting. Some oligocha3ts have 

 external gills (a few naids and tubificids). 

 The head is small and consists of the 

 prostomium, which is a small projection 

 in front of the mouth, and the peristo- 

 mium, which contains the mouth and 

 often appears dorsally like the first somite 

 of the trunk, but differs from the somites 

 in that it has no setae. 



Paired ovaries and testes are pres- 

 ent (Fig. 479) ; a number of large 

 sperm sacs or vesiculae seminales act as 

 reservoirs of the sperm, in which the 

 sperm ripens as it comes from the testes, 

 and one or more pairs of pockets called 

 the receptacula seminis or spermathecae 

 receive the sperm of another animal dur- 

 ing the act of pairing. The eggs and sperm are extruded into a capsule 

 called the cocoon which is secreted by a thickened portion of the integu- 

 ment called the clitellum. Development is direct, the young animal being 

 born with the form of the parent ; of the numerous eggs in a cocoon only 

 a few, sometimes only one, hatch out. Many oligochaets reproduce asex- 

 ually, by transverse division, and the regenerative powers of all are great. 



* See "A Monograph of the Order Oligochaeta," by F. Beddard, 1893. "Notes on 

 Species of North American Oligochaeta," by F. Smith, Bull. 111. St. Lab., Vol. 4, p. 285, 

 1895. "Notes on Species of N. A. Oligochaeta, II," by same, same jour., Vol. 4, p. 



Fig. 478 



Fig. 479 



Fig. 478 Diagram of the an- 

 terior portion of an earthworm, 

 Lumbricus terrestris (Sedgwick 

 and Wilson). 1, prostoraium ; 2, 

 mouth ; 3, openings of the sper- 

 mathecae ; 4, openings of the ovi- 

 ducts ; 5, openings of the sperm 

 ducts ; 6, clitellum. Fig. 479 

 Diagram of the anterior portion 

 of an oligochaet (an enchytraeid), 



showing the internal organs with 



1 the rigl 

 hand male organs and the left- 



the digestive tract and the right- 



hand female organs removed (Gal- 

 loway). 1, prostomium ; 2, brain; 

 3, mouth ; 4, ventral nerve chord; 

 5, spermathecae; 6, nephridium; 

 7. testis ; 8, clitellum ; 9, sperm 

 duct ; 10, ovary ; 11, sperm sac ; 

 12, oviduct ; 13, egg sac. 



