soon after their passage from the host and if manure is not examined 
promptly after it is passed, larvae will be found instead of eggs. The 
eggs of S. westeri are thin-shelled, 40 to 52 microns long by 32 to 40 
microns wide, deposited in strings, similar to those described by 
Ransom for S. ovocinctus from the prong-horned antelope. The 
rhabditiform larva is 495 to 525 microns long by 15 to 20 microns wide. 
Among the most important of the spirurid worms of the horse are 
the stomach worms belonging to the genus Habronema. The eggs of 
H. muscae (Fig. 43) are thin-shelled and are 40 to 50 microns long by 
Fig. 43. Habronema muscae. Eggs, a, b, c, d, early stages of development; e, con¬ 
taining embryo doubled on itself; f, with embryo almost straightened out; 
g, h, i, with flexible egg shell applied to embryo in a manner 
resembling that of a cuticle. From Ransom, 1913. 
10 to 12 microns wide in an early stage of development in the uterus. 
As the embryo develops the egg becomes longer and at a stage where 
the embryo is doubled on itself is 87 microns long and about the same 
width as given above. Later the shell becomes closely applied to the 
embryo except in the tail region and in this stage the shell is very 
suggestive of a cuticle. The embryos are 85 to 100 microns long by 
5 to 7 microns wide, with a rounded anterior end. The eggs of H. 
microstoma are oblong and truncate, and are 45 to 49 microns long 
by 16 microns wide. The embryo is 90 to 98 microns long. The eggs 
of H. megastoma are elongate, 40 to 57 microns long by 10 to 18 
45 
