28 BULLETIN 597,, U. S. DEPARTMENT OF AGRICULTURE. 



the stalk has never been observed to be inserted for its full length. 

 Often it extends to such a slight depth that after a few days the egg 

 may be found lying lengthwise upon the lips, yet firmly attached to 

 the hair. The color, a jet black, so conceals the attachment to the 

 transparent hair that it appears that the hair extends through the 

 center of the stalk portion and through a portion of the side of the 

 egg. The extreme point, however, shows a folding about the hair 

 which may be attributed to the pressure when it is inserted in the 

 pore of the skin. Above the stalk portion the hair is attached to 

 the side of the chamber containing the larva in a similar manner to 

 the attachment of other Gastrophilus eggs upon the hair. 



INCUBATION AXD INGRESS OF LARVAE. 



Having observed eggs upon both moist and dry portions of the 

 lips of horses, large numbers in various stages of incubation were 

 removed and placed in tubes for observation. About 100 were kept 

 in a test tube, with a moist cotton stopper, at the air temperature 

 of a living room. "While a variation in color was at first observed, 

 ranging from a black to a reddish color, after a few days the major- 

 ity were of a reddish brown. Some were placed upon a slide and 

 moistened, then by the use of two dissecting needles dead larva? were 

 removed. Xo larvae had hatched of their own accord, but emerged 

 when subjected to moisture and friction. In similar tubes which 

 were kept dry three lots of eggs varying in color were observed and 

 not a single larva hatched. 



Examinations of the inside of horses' lips revealed numerous holes 

 accompanied by much soreness which appeared as though the young 

 larva? hatched and had burrowed through the lips. Upon dissec- 

 tions in post-mortem examinations it was disclosed that the injury 

 was caused by " wild barley " or " foxtail grass.*' This grass was 

 determined by the Bureau of Plant Industry as Bordeum jubatvm. 

 Its injuries are more noticeable upon lips of livery horses when fed 

 hay containing this grass, as pastured animals avoid eating it and 

 the injury is less noticeable. It is worthy of note that this grass, 

 in addition to its injury upon lips of horses, serves as a winter host 

 of the black rust which is so destructive to wheat in the Dakotas. 



On August 24, 1915. a suckling colt, its mother (a crippled horse) 

 and another horse were carefully freed of eggs. Twenty-four hours 

 later a diagram was made showing the exact location of each egg 

 deposited during this time. Upon the following three days it was 

 too cloudy for other adults to oviposit, so the horses were not kept 

 in a barn to prevent further ovipositions. but were left to graze in 

 the JDasture. This allowed ample time for development of the 

 embryo and of a distinguishing brownish-red color which greatly 

 aided in keeping track of the eggs. 



