Season of attack by fly, hibernation, botfly of sheep, mode of attack, embryo, defensive acts of sheep, habitat of larva, mature larva, its exit, chrysalis in soil, its transformation. Symptoms, sneezing, snuffling, rubbing of nose, lachrymation, unsteadiness, discharge, respiratory digestive and febrile disturbances, emaciation, septic action. Lesions, larva, congestions of mucosa, brain. Treatment, warmth, errhine, parasiticides, mechanical extractors, trephining, injections. Prevention, newly turned furrow, quicklime, tar. Other larva in nose. Sheep are especially subject to the attacks, in summer and autumn and in warm sunny barns even in winter, of the Œstrus (Cephalemia) Ovis, the larva of which hibernates in the nasal sinuses or turbinated bones. The =sheep-bot-fly= is only about four lines in length, of a light yellowish or slightly brownish gray hue, hairy, with dull black transverse lines on the upper surface of the thorax, and a lighter color on the abdomen where the black lines are more broken. The transparent, colorless wings extend beyond the body: winglets are long and cover the poisers: abdomen is formed of five rings. They appear during the whole summer hiding away in walls, stumps and grass, unless when pairing or pursuing the sheep to deposit their young. The mode of attack is difficult to follow on account of the small size, gray color and rapid flight of the fly and fear and shyness of the sheep. It cannot be doubted, however, that they approach and drop on the margin of the nostril, the larva previously hatched from the egg. The old authors describe the deposition of the egg on the margin of the nostril and its prompt hatching by the animal heat, but the observations of Brown, Kelly, Cockrill, Riley and Ormerod abundantly prove that the fly is viviparous. Cockrill obtained no less than 300 live hatched larvæ from one fly caught while pursuing a sheep. The sheep seek to avoid the fly by resorting to dry dusty roads where they lie with the nose close to the ground, or they stand with the nose close to the soil and between their fore legs. At other times they will collect in a dense phalanx with their heads directed toward the centre of the mass and held low so that the fly cannot reach them. The moment the fly touches the nose they shake the head, stamp with the feet, and gallop off with the nose close to the ground, looking from side to side to see if the fly pursues and frequently smelling at the grass as if apprehensive of other flies hidden there. If such appear they instantly turn and scamper to other parts of the field or take refuge in a dry dusty place or gravel bank.