b BRITISH WELL-WORMS. 



graph, p. 19). Along with this we nnd also a remarkable 

 specialization of the nerve-cord in some of the segments — a 

 peculiarity which it shares with some of the Enchytraeids. 

 Leydig and others have further pointed out the existence of 

 valves in the dorsal blood vessel. While these appliances are 

 general in the earthworms they are rarely found in the lower 

 annelids, so that Phreovyctes in this respect is to be regarded as a 

 highly important type. Mr. Beddard in 1895 accorded to the 

 genus a position of great significance ; and though Michaelsen 

 has since reviewed the position, and my own discovery has yet 

 to be considered, I cannot refrain from summarizing the findings 

 of our greatest authority on this important subject. 



The question which Mr. Beddard asks is : — " How far are 

 we justified, with our present knowledge, in separating the 

 aquatic from the terrestrial Oligoclnela ?"' His answer shows 

 that in his judgment the genus under review forms in many 

 respects a very decided connecting link l)etween the two. 

 " There are, undoubtedly, a certain number of points in which 

 all these (aquatic) forms agree to differ irom the terrestrial 

 Oligochaeta. . . And there are, furthermore, a few points 

 which at present are peculiar to the aquatic Oligochaeta. We 

 will commence with the latter. Among all the Oligochaeta which 

 belong to Claparede's ' Limicolae,' the o\ a are of large size and 

 full of yolk ; this holds good, without a single? exception, from the 

 smallest Enchytraeid up to so large a form as PJii'coi'cytes. 

 The remaining point of difference concerns the structure of the 

 body wall. The longitudinal fibres consist of a single row of 

 deep fibres only (in the Limicolae or aquatic forms); this, how- 

 ever, does not characterize Phrcoiyctes, a genus which in other 

 characters occupies an intermediate position." Mr. Beddard 

 proceeds to examine the large and instructive group of worms 

 known as Enchytraeids, and adds — " The Enchytraeidae perhaps 

 resemble Phreoryctes more than any other group of the higher 

 Oligochaeta ; these resemblances, however, are not numerous, 

 and are confined to a few species. The most striking is the 

 existence in various species of Pachydvilns of the segmentally 

 arranged lateral outgrowths of the nerve-cord ; structures similar 

 to these appear to occur in Phreojyctfs. Besides Phreoryctes, the 

 only Oligocha-ta in which there ate so few as four S!jt;c per seg- 

 ment, implanted singly, is Enchytraeus nioiiocha-fiis." It was this 

 fact tliat led me to name the Essex worm Dichacta, or the worm 



