AN ATTEMPT TO CLASSIFY EARTHWORMS. 219 



in each somite^ and may be capillary^ uncinate, forked, or 

 simple. The clitellum is always developed round the male 

 pores, and generally occupies only two somites. There are no 

 nephridia in the genital somites. There is no true gizzard, 

 no typhlosole, no subneural vessel. [These last four negative 

 characters, however, hold for some " earthworms."] 



The characters nearly constant in Order 2, in which 

 ^'earthworms" differ from water- worms, are — 



Large size, varying from two inches (or less) to six feet ; 

 thick, pigmented, and opaque body-wall, though the pigment 

 may be absent and the wall more or less transparent on the 

 ventral surface. 



Prostomium separated by a groove fi-om the peristomium. 



Setae frequently not arranged in groups ; when they are so 

 arranged there are never more than two setse in a group 

 (?Echinodrilus, Vaillant). These setae are nearly always 

 simple, or the modification when present takes a different 

 direction from that in Order 1. 



The clitellum varies in position with regard to the male 

 pores, and always occupies more than two somites (? certain 

 species of Perichseta). 



A gizzard is nearly always present, except in such cases as 

 Criodrilus, Pontodrilus, Microscolex, and Photo- 

 drilus, where the character of the food renders it useless.^ 



With the exception of a few genera, nephridia occur in all 

 somites after the third or fourth, including the genital 

 somites. 



Order 1 includes Vejdovsky's '^ families" Discodrilidse, 

 Enchytrseidse, Tubificidse, Phreoryctidae, and Lum- 

 briculidse. 



Order 2 contains the remainder of his families, and these 

 I will now proceed to group as follows : 



Branch I. Plectonephrica.^ 

 Excretory system in the form of numerous delicate tubules 



^ In Pontodrilus there is a modification of the gut-wall which probably 

 represents the gizzard. 

 2 nX£Kr>; = a net. 



