45 



SOME NOTES ON BRITISH FRESHWATER RHAB- 

 DOCOELIDA A GROUP OF TURBELLARIA. 



By Henry Whitehead, B.Sc. 



(Read January 28th, 1913.) 



Plate 4. 



The members of the group Rhabdocoelida are very similar as 

 regards appearance, shape and movements to the Infusoria, 

 though they are generally much larger and their complicated 

 internal structure enables them to be distinguished at a glance. 

 The Rhabdocoelida form a branch of the group Turbellaria, 

 to which the larger Planarians found in fresh water also belong. 

 The Turbellaria, in turn, together with the Liver-flukes and 

 Tape-worms, are included in the phylum Platyhelminthia 

 or Flat-worms. 



The British marine Turbellaria have been monographed by 

 Prof. Gamble (12), and our President has taken an active part in 

 the study of the land Planarians of Australasia. The freshwater 

 Turbellaria have apparently received but little attention in this 

 country, though Prof. Gamble publishes a list of British species 

 in the Cambridge Natural History (14). 



As the larger freshwater Planaria (Tricladida) cannot be 

 regarded as microscopic objects, and are therefore of no special 

 interest to the Club, the writer proposes, in this paper, to deal 

 only with the group Rhabdocoelida. 



Yon Graff has written two monographs on this group, and has 

 devoted much time to valuable work on anatomical features ; 

 and it is chiefly from these sources that the information con- 

 tained in this paper has been derived. 



The writer does not propose dealing in detail with the 

 anatomy, but rather to deal with the Rhabdocoels from a general 

 point of view, emphasising matters of particular interest to the 

 field naturalist. 



The freshwater Rhabdocoels vary in size from 1/2 5th to half 



