156 OLIGOCHAETA 



is as follows — (i) Lumbricinae (Lumbricus) ; (2) Tubificidae {Tiibifex, Lumbriculus, Rhynchelmis) ; 

 (3) Enchytraeidae {Enchytraeus) ; (4) Naideae {Dero, Nais, Aeolosoma, Chaetog aster). 



The ' Greminipares ' are distinguished from the ' Agemmes ' by the fact that the sexual organs 

 are always present, while in the 'Agemmes' the sexual organs only make their appearance at 

 certain times. 



The Lumbricidae, Tubiiicidae and Enchytraeidae are separated by the following characters. 



CLAPAKi]DE distinguished the Oligochaeta from other Annelida and divided them into two groups. 



(i) Terricolae. With two ventral blood-vessels (one above, one below the nerve-cord) with 

 ' segmental organs ' in the segments which contain the spermathecae and reproductive ducts ; the 

 clitellum developed behind the male sexual pores ; a vascular network on the segmental organs. 

 Genera Lumbricus and probably Hypogaeon, and Criodrilus. 



(z) Limicolae. With one ventral blood-vessel (above the nerve-cord) without segmental organs 

 in the genital segments; the male-pores opening on to the clitellar segment. No vascular network 

 on the segmental organs. 



Genera Tubifex, Limnodrilus, Clitellio, Lumbriculus, Nemodrilus, Enchytraeus, Pachydrilus, Nais, 

 Stylaria, Chaetogaster, Euaxes {=Bhynchelmis), Serpentina, Aeolosoma. 



The next classification of the group is that of G. Johnston. The division of Oligochaeta 

 (termed by him Sooloces) included also the Capitellidae ; it was divided into two tribes : — 

 I. Lumbricina. II. Naidina. 



The Lumbricina were again divided into two families : — 

 (i) Lumbricidae, genera Lumbricus, Saenuris, Enchytraeus; 

 (2) Littorales, Clitellio, Valla { = Capitella). 



The Naidina has only one family Naidea with genera Proto, Stylaria, Seipentina, Nais, Chaetogaster. 



The classification of Leon Vaillant is as follows : — 



Order Annelides lombkicines. 



I. Lumbricina. Setae simple. 



(i) Lumbricina propria. Setae isolated or grouped in pairs. Perichaeta, Megascolex, Pontoscolex, 

 Hypogaeon, Echinodrilus, Lumbricus, Helodrilus, Criodrilus, Euaxes, Trichodrilus, Phreoryctes. 

 (2) Enchytraeina. Setae three or four in number,in each bundle. Enchytraeus, Pachydrilus. 



II. Naidea. Setae bifid or hair-like, at least partly, rarely pectinated. 



(i) Naidea propria. Setae in four rows, exceptionally biserial, and then all hair-like. 

 Heterochaeta, Stylodrilus, Lumbriculus, Clitellio, Tubifex, Nais, Aulophorus, Mesopachys, 

 Aeolosoma. 

 (2) Chaetogastrina. Setae biserial, never hair-like. Chaetogaster, Ctenodrilus. 

 Benham (1) has proposed a classification which is really not different from that of d'Udekem. 

 He divides the class into two sub-classes : — 



I. Naidomorpha. II. Lumbricomorpha. 



In the first sub-class are the families Aphaneura, Naididae, Chaetogastridae (and the genus 

 Ctenodrilus). 



It is defined thus :— ' Small worms of relatively few somites ; blood uncoloured ; male genital pores 

 in front of the seventh somite, or in this somite. Asexual as well as sexual reproduction occurs.' 



The Lumbricomorpha are thus defined :—' Reproduction only by sexual process; no cephalization ; 

 somites behind the peristomium all similar; and setae are similar throughout the body, except in 

 special regions, e.g. on clitellum. Male genital pores behind the seventh somite. No eye spots 

 (7 Helodrilus, Hopfmeistbe). 



