GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 27 
a horse is grazing or otherwise protected from ovipositions. She 
usually comes from a distance and strikes at the lips. Her quick 
fiight seems to be distinguished by the male, who attempts to mount 
her before she oviposits, but the momentum of the two usually carries 
the couple to some distant place so quickly that one can not tell 
whether copulation actually takes place upon the wing or whether 
they fall tothe ground. At any rate, they fly for some distance. Ap- 
parently the sexes always meet at the horse, the males awaiting the 
approach of the females. At times the male encounters an adult 
female of G. intestinalis about the horse, and these two may be ob- 
served to fall upon the grass at the feet of the horse, usually separat- 
ing within a few seconds. 
PREOVIPOSITION PERIOD AND OVIPOSITIONS. 
Just how soon after emergence copulation takes place is not 
definitely known, but it is certainly less than 18 hours. Adults 
emerging during the night copulate by noon of the following day 
and will oviposit during that afternoon. They will not oviposit in 
captivity. On five occasions in which flies emerged normally during 
the night, males and females were kept in a box with glass sides and 
with green foliage. By noon in each case some were observed to 
copulate and when;liberated in the afternoon would oviposit. Their 
wings were colored with red ink, and when captured they could be 
identified easily. Wnder favorable conditions ovipositions took place 
as soon as adults were liberated, usually about 3 hours after copula- 
tion. After a lapse of a few minutes they were never to be col- 
lected about the same bunch of horses, which is probably due to the 
migration of adults and to the movements of the various horses upon 
which they oviposit. 
A determination of the egg-laying period is important in that it 
shows the value of destroying adults at different times during this 
stage, but with such short precviposition and longevity periods and 
the inability of flies to feed, the indication is that the flies oviposit 
throughout their existence. Dissections of females reared to adults 
indicate that they develop from 134 to 167 eggs, the usual number 
possibly being near 150. 
Unlike G. intestinalis, which may stand in midair and consecu- 
tively deposit 15 or 20 eggs at one time, often placing two or more 
upon one hair, G': haemorrhoidalis deposits but one at a time and 
only one upon ahair. It leaves the animal for about one-half minute 
or longer after ovipositing, but not for so long a time as does 
G. nasalis. It never oviposits upon any other portion except the 
lips, preferably the portions moistened by saliva. The stalk portion 
of the egg is inserted in the pore of the skin at varying depths, but 
