THE STRUCTURE AND SYSTEMATIC POSITION 
OF STEONGYLUS POLYGYRUS . 
By C. L. BOULENGER, M.A., D.Sc. 
(From the Zoological Department , University of Birmingham.) 
(With 4 Text-figures.) 
Dujardin (1845) was the first to give a satisfactory account of the small 
Strongylid worms inhabiting the intestinal tract of field-mice and voles. His 
descriptions of the various species were careful and for the most part accurate, 
they were, unfortunately, not accompanied by figures, and incomplete in 
that the characters of the bursal rays of the males were not given, an omission 
which has led to considerable confusion, since the modern classification of the 
Trichostrongylidae is based largely on the structure of the male bursa. 
Of the four worms described by Dujardin, Strongylus costellatus has been 
taken as the type of the genus Heligmosomum Railliet and Henry (1909), to 
which genus his other species S. minutus, S. laevis and S. poly gyrus were also 
assigned. On the authority of Travassos (1914) S. polygyrus has since been 
removed to his genus Viannaia by Hall (1916) who, however, remarks that 
the available descriptions are not sufficiently detailed to warrant the change. 
I have recently been fortunate in obtaining a number of small Strongylids 
from the intestine of Microtus ( Arvicola ) agrestis L. from the neighbourhood 
of Birmingham, which I am convinced belong to the same species as that 
described by Dujardin as S. poly gyrus, their study has enabled me to clear 
up a number of misconceptions with regard to this form. 
Von Linstow (1878, 1879 and 1882) is the only authority since Dujardin 
who has attempted to reinvestigate the species; his account contains descrip¬ 
tions and figures of the male bursa, but in certain important characters the 
worm studied by him seems to deviate so much from the original specific 
diagnosis that Hall (1916) felt justified in concluding that a different form had 
been dealt with by the German helminthologist, and in removing it to a new 
genus Heligmosomoides under the designation H. linstowi Hall. Travassos 
(1921) accepts Hall’s conclusions and in his recent monograph on the Tricho¬ 
strongylidae we find S. polygyrus Dujardin listed as Viannaia polygyra and 
S. poly gyrus von Linstow as Heligmosomoides linstowi. 
