142 FRIEND : NEW AND LITTLE-KNOWN OL1GOCH& I S. 



of our investigations. Having been for some years engaged in 

 collecting specimens from various parts of the United Kingdom, and 

 being now in possession of much valuable information relating to 

 the limicolous Oligochaets of Great Britain, I propose to issue from 

 time to time such reports on the species found within the field 

 of operations which comes under the purview of 'The Naturalist' 

 as I shall be able to prepare. I shall begin with a selection of such 

 worms as are already known to occur in this country. The species 

 in my possession which have only been described as Continental or 

 are new to science will be dealt with later. 



It will be well to preface my first description with a few remarks 

 respecting the scientific characters of this group of Oligochaets. As 

 Eeddard has summed up the results of earlier modes of classification, 

 I shall not refer to them. It may suffice to note that the Limicohe 

 differ from the Terricolae mainly in the following particulars : — The 

 ova of the former 'are of large size and full of yolk . . . the egg-sac> 

 are of large size and extend through several segments ; both they 

 and the sperm-sacs are very thin walled, and their interior is entirely 

 undivided by trabecule ; in all, or at least very nearly all, of the 

 aquatic Oligochaeta there is a head-pore, a structure which is, so far 

 as our knowledge at present goes, quite unrepresented in the 

 terrestrial Oligochaeta 7 (Beddard, 'Monograph of Oligochaeta,' 

 P- I 57)- r Fh e presence of the head-pore in the embryo of certain 

 terrestrial forms is a point of special interest for the evolutionist. 

 4 Besides these resemblances, all the aquatic Oligochaeta agree in 

 a number of structural features, which would, if it were not for the 

 family Moniligastridae, distinguish them from all the terrestrial 



Oligochaeta. These are : — 



i. The clitellum is only a single layer of cells thick. 



2. It has a very anterior position, more so than in any terrestrial 



3. The male pores are also far forward. [form. 



4. The sperm duct traverses only two segments. 



If we add the family Moniligastridae, it seems to me that a perfectly 

 natural group of Oligochaeta will be the result; this group will be 

 capable of the following definition: 



'Oligochaeta with a clitellum commencing not later than the 

 tenth or eleventh segment, and consisting of only a single layer 

 of cells ; sperm ducts only occupy two segments, the external pore 

 being on the segment following that into which the funnel opens : 

 male pore situated in front of the female pore; eggs generally large, 

 always provided with abundant yolk; egg-sacs large; spermiducal 

 lands, when present, possess a muscular layer interposed between 

 the inner epithelium and the glandular layer: sexual maturity at 



Natura . 



