REVIEW OF THE NEMATODE GENERA SYNGAMUS SIEB. 
AND CYATHOSTOMA E. BLANCH . 1 
By Edward A. Chapin 
Zoological Division , Bureau of Animal Industry , United States Department of 
Agriculture 
INTRODUCTION 
Following the collection of a species 
of Cvathostoma from the red-tailed 
hawk ( Buteo borealis ) the writer has 
found it necessary to go into the 
question of the various described species 
of Syngamus and Cyathostoma in order 
to determine the status of the above- 
mentioned form. This investigation 
has shown that the species from the 
hawk is apparently new to science and 
in addition it has brought out several 
facts relating to the species of these two 
genera that seem to render desirable 
a general taxonomic review of the 
genera. The only previous paper of 
a similar scope is one in Russian by 
Skrjabin (1915), which is not readily 
available to most workers. 
The collections of the U. S. National 
Museum contain abundant material for 
study of three species; H. A. Bavlis, of 
the British Museum (Natural History), 
has kindly lent two pairs of a worm 
from an Old World corvine bird, and 
Herbert Fox, of the Zoological Society of 
Philadelphia, through F. D. Weidman, 
has submitted for study a series of 
specimens from three avian hosts. 
Thanks are extended for this coopera¬ 
tion and to B. H. Ransom for his helpful 
criticism. 
The differential characters of value 
in the diagnosis of species of these 
genera have not as yet been well for¬ 
mulated and the separation of species 
on the basis of existing descriptions is 
in some cases difficult or impossible. 
Leiper (1913) in a paper on Syngamus 
kingi has made a useful contribution 
toward the formulation of characters 
that may be employed in the recogni¬ 
tion of species. Though his paper has 
to do with the genus Syngamus only, 
some of his differentials may be applied 
to Cyathostoma equally well. He 
suggests as diagnostic or differential 
characters the following: (1) Relative 
position of buccal capsules in paired 
specimens; (2) relative length of esopha¬ 
gus to that of the body; (3) size and 
armature of mouth capsule; (4) relation 
of axis of buccal capsule to that of 
body; (5) outline of optical section of 
chitinous wall of capsule; (6) size of 
spicules; (7) configuration of posterior 
end of body of female; (8) site of 
excretory pore. 
The first of these differentials of 
course can be used for only the species 
of Syngamus and then must be used 
with discretion. In young specimens 
of S. trachea the capsule of the male 
may be as much as half the length of 
the male in advance of the capsule of 
the female. On the other hand, there 
are before the writer gravid specimens 
of this worm from the turkey in which 
the capsule of the male is only slightly 
in advance of that of the female. This 
variation is due to the fact that the 
male changes little in length after 
maturity is reached, while the develop¬ 
ing eggs cause apparent growth in 
length of the female. The second 
character mentioned by Leiper is 
apparently valid so far as the males are 
concerned, but is influenced in the 
case of the females by the factor 
mentioned above. The other differ¬ 
entials noted by Leiper appear to hold 
for both sexes at any age, with the 
possible exception of the last. The 
excretory pore is subject to a slight 
apparent migration with the egg 
development. 
On the other hand, Leiper does not 
consider the bursa of the male. In the 
species of Cyathostoma there is no 
trouble involved in an examination of 
this organ. In Syngamus, with reason¬ 
able care, a preparation of the bursa of 
the male can be made without serious 
damage to the female worm. If with 
a sharp knife the genital cone of the 
female worm is removed from the body, 
the male worm with bursa entire comes 
away at the same time. A few 
minutes’ careful work with a needle 
suffices to remove from within the 
bursa the fragments of the female 
genital cone, and the male may be 
then treated as any strongyle. If the 
pair of worms has been carried into 
glycerine before this operation is at- 
1 Received for publication June 24, 1924, issued June, 1925. 
Journal of Agricultural Research, Vol. XXX, No. 6 
Washington, D. C. Mar. 15, 1925 
Key No. A-81 
19975—25t 
5 
(557) 
