Volume XIV 
APRIL, 1922 
No. 1 
OBSERVATIONS ON CERTAIN CESTODES OF RATS, 
WITH AN ACCOUNT OF A NEW SPECIES 
OF HYMENOLEPIS. 
By H. A. BAYLIS, M.A., D.Sc. 
(Published by 'permission of the Trustees of the British Museum.) 
(With 4 Text-figures.) 
During some investigations in which he has been engaged on the internal 
parasites of rats in the British Isles, Mr G. C. Dudgeon, of the Wellcome 
Bureau of Scientific Research, has kindly submitted to the writer examples 
of all the species of adult Cestodes found. 
Two species of Hymenolepis are well known to occur in the brown and 
black rats, viz. H. diminuta and a smaller form most commonly referred to in 
literature as H. murina. The latter is of exceptional interest on account of 
the vexed question as to its identity with the human parasite H. nana. In 
more or less direct connection with this question a very extensive literature 
has grown up, which it is impossible to review fully here. It may be said, 
however, that the general result of researches by numerous authors, while 
still inconclusive, tends to show that the forms occurring in man and the rat 
are morphologically identical, while on physiological grounds there is some 
justification for regarding them as distinct species, subspecies, or at least 
varieties. This view is held on account of the many unsuccessful attempts 
that have been made to infect rats with H. nana of human origin, and on the 
other hand to infect man with “ H. murina 
A few of the more important contributions to the subject may be men¬ 
tioned. The celebrated researches of Grassi and his collaborators (1887-1892) 
along these lines led them to regard nana as a variety of “ murina f and they 
concluded that infection was capable of transmission from rats to man, though 
the experimental evidence was very scanty. On the other hand, on morpho¬ 
logical grounds, as well as from considerations of geographical distribution, 
other authorities (Moniez, Blanchard, von Linstow) regarded the two forms 
as distinct species. The last-named author (1896) gives comparative measure¬ 
ments and other data compiled from his own and numerous other authors’ 
observations, which he appears to have regarded as conclusive, but which 
have not proved equally convincing to later writers. Stiles (1906) favoured 
the separation of the forms as “host subspecies,” and renamed “//. murina" 
Parasitology xiv 
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