218 W. B. BENHAM. 



anterior few somites of the body are frequently different from 

 the following somites, e.g. in Naids and in Chsetogaster 

 the setse have a different arrangement or form in the anterior 

 somites (" cephalization " of Lankester) ; or the prostomium 

 is pigmented and ciliated, as in ^olosoma and Cteno- 

 drilus. Eye-spots are frequently present. 



Sub-class II. LUMBRICOMORPHA. 



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 Somite vii. 



No eye-spots (? Helodrilus, Hoffmeister). 



The various families included in this sub-class cannot really 

 be sejDarated by any very marked anatomical characters; but 

 they may be divided roughly into — 



Order 1. Microdrili (Lumbricomorpha minora) ; 

 2. Megadrili (Lumbricomorpha majora); 

 which correspond to '' water-worms " and " earthworms " re- 

 spectively. The only constant difference between these two 

 groups is the absence in Order I of a capillary network of 

 blood-vessels on the nephridium, and the presence of such 

 blood-vessels on the nephridium in Order 2; and this is very 

 likely due to the difference in size, and to the character of the 

 medium in which the members of the two groups live. 



Other characters which are usual to Order 1, and rarely 

 present in Order 2, are as follows : 



Small size, and thin, transparent body-wall. 



Prostomium not separated from the peristomium by a 

 groove. 



Setce always in four groups per somite, and usually more 

 than two in each group : frequently the setse are of two sorts 



^ In a paper on a uew species of Diacliitta, a proof of which Professor 

 Lankester has very kindly allowed me to sec, ]\Jr. Beddard slates that no seta: 

 arc present on the Qrst five somites. 



