of OUgochcetous Annelids. 91 



gards food, attaining sexual completeness in winter as well as 

 in summer, unchecked by any competition or by assailants. 



1. Families of the Oligochseta. — The Oligochjeta are best 

 primarily divided as proposed by M. Clapar^de, into the 

 Terricolce and the Limicolce. The former group has been but 

 little studied, with the exception of the typical genus Lum- 

 hricus^ and is not as yet broken up into families ; it includes 

 the genera LumbricuSj PericJueta, Phreoryctes and others, 

 characterized by much greater histological and organological 

 differentiation than is met with in Limicolffi. The Limicolffi 

 liave been divided into three families, Sa3nurida3, Enchytraiidae, 

 and Naididffi ; but I should be inclined to place the Enchy- 

 trffiidge as a subgroup with Sa?nurid£e, since only in this way 

 can full weight be given to the very distinctive characters of 

 the Naididge. We thus have Lumbricidge = Terricolce, whilst 

 Sfenuridfe and Naididffi = Limicola3. TheNaididae are further 

 divisible into Naidinai and Chgetogastrinae. 



2. New Species of Sa^nuridfe. — The determination of spe- 

 cies amongst these worms is very difficult, for two reasons : — 

 first, that authors are not agreed as to what characters are 

 important, and give descriptions of varying incompleteness ; 

 and secondly, that it is not possible as yet to say what are the 

 limits of variability and the phases of development in one and 

 the same species. 



The most abundant wonn in the Thames mud is the Tubifex 

 7-ivulorum, described some years since with much care by M. 

 Jules d'Udekem. Two other worms, however, are very abun- 

 dant, living inextricably mixed with it in masses : these are 

 a sj)ecies of Limnodrilus and another, very interesting Tubifex. 

 No observer has recorded Limnodrilus (of Claj^ar^de) in Eng- 

 land ; but I have found it abundantly in many localities, re- 

 presented by three species. That in the Thames appears to be 

 the first of M.Clapar^de's species, L. Udekemianus (Recherches 

 sur les Oligochetes) , being characterized by brown patches in 

 the posterior segments, caused by stellate pigment-cells form- 

 ing the endothelium of the perivisceral cavity (figured by me 

 in Quart. Journ. Microsc. Science, July 1870). Another Lim- 

 nodrilus, which I have obtained from an old pond at Hamp- 

 stead, differs from either of Clapar^de's species in its great size 

 (4 inches in length) , as well as in the number of the setae. In 

 another series of specimens, which I think will prove specifi- 

 cally distinct, the chitinous tube in the copulatory organ is of 

 enormous length as compared with those figured by the Swiss 

 Professor. I have found that specimens of these and other 

 worms may be mounted with great facility, and kept for 

 reference, by means of glycerine jelly. 



7* 



