A MONOGRAPH OF THE OLIGOCHAETA. 



Class OLIGOCHAETA, Gkube. 



Def. Segmented ' worms ' invariably hermaphrodite ; all the segments of the body — 

 except the first and occasionally an additional and varying number at anterior end — 

 setigerous, the setae usually /-shaped but showing variation in form, never borne upon 

 parapodia. Excretory organs paired tubes metameric, or numerous in each segment 

 and dysmetameric. Branchial organs, rarely present. Gonads limited in number 

 (normally never more than two pairs of ovaries and testes) ; sexual products nearly 

 always matured in special sacs developed from the septa. Special ducts carry off the 

 genital products. Development direct. Terrestrial or fresh water, rarely marine, in 

 habitat. 



PAET I. 



THE ANATOMY OF THE OLIGOCHAETA. 



§ I. Historical Note. The Bibliography appended to the present work shows how very recent is our 

 knowledge of the anatomy of the Oligochaeta. Of the exotic earthworms, which form so much the 

 greater portion of the known species, there was absolutely no anatomical knowledge until the 

 publication of Vaillant's memoir upon Perichaeta in 1868 (3) ; all that was known before this 

 date from the contributions of F. S. Leuckakt, Rapp, Templeton, and Schmaeda relates to little 

 beyond external characters. Peekiee's researches, particularly his first memoir (6), gave the 

 first indication of the very great structural variation exhibited by the terrestrial Oligochaeta. Since 

 that date (1871) our knowledge has rapidly accumulated, particularly during the last ten years, by 

 the investigations of Hoest, Michaelsen, Rosa and others upon the continent, Spencee and 

 Fletcher in Australia, Eisen in America, and Benham and myself in England. 



Before 1868 we were only acquainted with the structure of European Oligochaeta. The common 

 earthworm (represented no doubt by several species) furnished material for a number of investigators ; 



B 



