208 
Strongylus polygyrus 
male organs, the spicules are, however, given as 0-58 mm. long, this measure¬ 
ment agreeing well with von Linstow’s (0-54 mm.) and that observed by me 
in the new material (0*5-0*58 mm.). 
Von Linstow’s description and figures of the male bursa have given rise 
to much discussion; according to his account the bursa of S. polygyrus has 
no separate dorsal lobe and no median dorsal ray, the latter being replaced 
by two rays with separate origins; between these and behind the cloaca are 
shown seven pairs of small ray-like structures ending in papillae. The bursal 
characters as figured by von Linstow differ so much from those of other species 
now assigned to the genera Heligmosomum and Viannaia as to justify Hall’s 
transference of the worm to a new genus Heligmosomoides. 
Travassos (1921) accepts the systematic position assigned to the species 
by Hall, but adopts a somewhat different interpretation of von Linstow’s 
figures of the bursa; he prefers to regard the two dorsal rays as representing 
the externo-dorsal rays of other species, and the true dorsal rays as being 
replaced by the seven pairs of small post-cloacal rays. 
My material has shown that Travassos’ interpretation is the more correct. 
In the Birmingham specimens the male bursae bear a striking resemblance, 
both in shape and in the general arrangement of the ventral and lateral rays, 
to those figured by von Linstow. When completely spread out and viewed from 
the dorsal or ventral aspect (text-fig. 3) the bursa is seen to be of considerable 
width with an almost straight dorsal margin, without a separate dorsal lobe 
or marked median incision. There are two long, slender externo-dorsal rays 
with separate origins, and, between them, a very small median dorsal ray 
branching dichotomously into four delicate branches. A genital cone is well 
developed, bearing one or two pairs of small, but highly retractile papillae 
on each side of the cloaca. 
In an incompletely extended bursa, as shown in text-fig. 4, the two externo- 
dorsal rays appear much closer together and the genital cone covers and hides 
the greater part of the dorsal ray, revealing only the tips of the four branches 
which, together with the cloacal papillae, give the appearance of a series of 
small rays in the neighbourhood of the genital opening. 
The peculiarities of von Linstow’s figures of the bursa of S. poly gyrus are 
thus readily explained; comparison of these figures (1878, Fig. 21 and 1879, 
Fig. 26) with my own (text-figs. 3, 4) will show conclusively that the form 
described here is specifically identical with that studied by the German 
authority. 
The facts stated above make it clear that there is no justification for 
the separation of S. polygyrus Duj. and S. polygyrus v. Linst. It is evident 
from the structure of the female tail and from the peculiarities of the male 
bursa that the species cannot be referred to either of the genera Viannaia 
or Heligmosomum ; Hall’s genus Heligmosomoides must therefore be re¬ 
tained, the worm, however, figuring as H. polygyrus (Duj.) instead of 
H. linstowi Hall. 
