igt4. WhiTKHOUSE. — 7/te Natural Hisiory of iPlaiiarians. 
THE NATURAL HISTORY OF PLANARIAXS. 
BY R. H. WHITEHOUSE, M.SC. 
(Read before the Belfast Natural History and Philosophical Society, 
December 9th, 19 13.) 
There are three elasses of flat-worms, known respectively 
as Turbellaria, Trematodes, and Cestodes ; the first of 
these have not even attracted the attention of the pubhc 
sufficiently to have given rise to a popular name ; the 
second class are popularly called " Flukes," and one or two 
of the best known give rise to " liver rot " in sheep ; the 
third class are called " Tape-worms," and are best known 
as parasites in domesticated animals. In this paper it 
is proposed to deal with the Turbellaria — so-called on 
account of the disturbances they produce in the water in 
which they live ; such disturbances, however, are of course 
exceedingly slight. There are three groups of Turbellaria, 
viz., Rhabdocoeles, which are aquatic or semi -aquatic ; 
Triclads, comprising both aquatic and terrestrial forms ; 
and Polyclads, which are marine organisms. The Triclads 
are divided into sub-groups according to their habitat, viz.. 
Freshwater (Paludicola), Marine (]\Iaricola) and Land 
Planarians (Terricola) ; of the freshwater planarians four 
species can be readily obtained in the Belfast district, 
though there are doubtless others too. Several marine 
forms are found on the shores of Belfast Lough, and Land 
Planarians are represented by Rhynchodcmus terrestris, 
w^hich is very common.^ Land Planarians, however, 
have their home in the tropics. 
The interest and importance of these lowly organised 
worms have not been overlooked by men outside the ranks 
of academic zoologists ; this is evident from the remarks 
of Professor J. A. Thomson in his presidential address to 
the Royal Physical Society of Edinburgh in 1912, on 
" Professor Bergson's Biology." He says : " With clear 
1 For localities and fi gures, see R. F. Scharff, Irish K^of., vol. ix., iqoo, 
pp. 216^-17. 
