DESCRIPTIONS OF GENERA AND SPECIES 229 



rivulorum does from Limnodrilus. In considering the question of the generic 

 separation of these forms, it must be borne in mind that the comparatively simple 

 organization of the family leaves less room for differences than in the highly organized 

 ' Terricolae.' As all or nearly all the generic names have been in use for so long, and, 

 as it is a less serious matter to multiply genera than to multiply species, I retain the 

 names as they are at present. As to the species it is generally impossible to follow 

 and compare descriptions by different authors. Minute points, emphasized by one, 

 are neglected by another. "What is wanted is a careful study of the living worms by 

 one naturalist who is able to devote a good deal of time to what is, after all, a very 

 small matter. 



ElSEN proposed (12) to divide the genera known to him into two sub-families, one containing the 

 genus Telmatodrilus alone, the others the remaining forms. 

 They are distinguished by Eisen thus': — 

 Subf. i. Telmatodrilus. 



Setae sigmoid, only bifurcate in young. 



Ventral nerve ganglia, distinctly paired, with numerous minute commissures. 

 Five pairs of contractile hearts (not more dilated than others) in vi-x. 

 Ventral vessel lateral in position approximated to dorsal. 

 Spermiducal gland with numerous (ten) separate prostates. 

 Subf. ii. Tubiflcini. 



Setae both capilliform and uncinate. 

 Ventral nerve-ganglia not separated. 

 One to two pairs of contractile hearts in viii, ix. 



Spermiducal gland with one large separate prostate, or without prostates. 

 To these subfamilies Stolc added two others, viz. Ilyodrilinae and Bothrioneurinae. He defines 

 these subfamilies and the Tubificinae as follows": — 

 Subf. i. Ilyodrilinae. 



No penis. Penial setae present. Spermathccae without spermatophores. 

 No prostates. Development of ova as in Naidomorpha. 

 Subf. ii. Tubificinae. 



Penis present, but no penial setae. Prostates present and spermatophores. 

 Development of ova as in higher Oligochaeta. 

 Subf. iii. Bothrioneurinae. 



Penial setae present, but no penis. Male genital pore single and median. 

 Prostates present. No spermatheca. 

 If it were desirable to subdivide the family Tubificidae, my genus Branchiura would certainly form 

 the type of a fifth subfamily. But it does not appear to me that much is to be gained by forming 

 subfamilies in a family of so comparatively limited an extent as the Tubificidae. 



As regards the mutual affinities of the genera comprising this family, we may 



arrive at a comparison of the genera by the help of the accompanying table, which 



shows the principal anatomical resemblances and differences. 



' I abstract the two definitions from Eisen's two papers. 



^ As nearly as I can make out from the paper, which is in Czech. 



