INTERNAL PARASITES 181 
Dispharagus uncinatus has been reported as occurring in the esoph- 
agus and proventriculus of geese, ducks and swans. They occupy 
cyst-like structures which are most frequently encountered in the wall 
of the proventriculus. When these are 
opened the worms are found surrounded by 
a bloody fluid or a yellowish caseous mass. 
The wall of the proventriculus is thickened 
and the mucosa is covered by a large amount 
of yellowish green viscid mucus. A stage of 
the life cycle of the parasite is passed in a 
certain aquatic form, Daphnia rulex. The 
embryos, free in the stomach of the bird, 
gain access to the water where they are 
taken in by the Daphnia, which creature is 
in turn eaten by the waterfowl. 
Prophylaxis must depend chiefly upon 
killing of infected birds, and upon keeping 
birds away from stagnant water, colored 
brownish or yellowish by the presence of 
Daphnia in large numbers. 
; : Sclerostomum anseris infests the gullet, 
FIG 2d ig epharagus proventriculus and gizzard of geese. It. 
view of anterior ex- burrows under the mucous membrane and 
foe ese 60 causes the formation of dark brown crust- 
like layers on the epithelium. In young 
ducks it causes gradual emaciation and debility. The location of 
the parasites discourages the use of antihelminthics. 
Hystrichis tricolor is a worm which infests the proventriculus 
of ducks, and causes extensive destruction of 
tissue. Very large ulcers are formed which al- 
most perforate the walls of the organ. Cysts 
about the size of a bean, containing the parasite, 
are also found. A similar parasite Hystrichis 
elegans also occurs in the proventriculus of 
ducks and of a large number of palmipeds. JH. 
cygnt occurs in similar location in the swan. Fic. 22. Hystrichis 
Tropisurus fissipinus form eysts in the sub- ae ore 
mucous region of the esophagus of ducks, some- 
times causing a fatal inflammation. 
Trichosoma contortum occurs in ducks and geese besides other 
birds. They infest the dilated portion of the gullet, which in ducks 
ae 
