DIPTEEA OK TRUE FLIES. 213 



pass over water, giving the cattle shelter either of trees or rough 

 hovels in the meadows, or turning them where they can run to 

 water for protection, is advisable. Remedial measures consist 

 of destroying or extracting the larva from the warble. Mercurial 

 ointment is a good remedy ; a small piece rubbed into the warble 

 when it has just opened will soon destroy the grub, and allow 

 the wound to heal up. Not only does the ointment kill the 

 larva by blocking up the air-pores or spiracles, but it destroys 

 the grub in the cell. Cart-grease and M'Dougall's smear have 

 similar effects, but are not nearly so certain in results. I 

 believe there is nothing like the old plan of squeezing out the 

 maggot and killing it at once, before the warble has become 

 too old. 



The Sheep Nasal-fly (CEstrus ovia). 



Sheep are often seen shaking their heads and stamping on the 

 ground ; at other times running about with their noses close to 

 the ground. These are symptoms that CEstrus ovis is about, 

 ready to lay its eggs. The fly appears in the summer ; it is a 

 dull-soloured insect, which we often see in sheep districts at rest 

 at dusk, and in cold weather on the sheep-pens and hovels near 

 the sheep. The eggs are laid on the sheep's nose, and the 

 maggots crawl up the mucous membrane and some enter the 

 sinus of the head. The majority live in the nasal passages, 

 and when mature are brought out on to the grass during one of 

 the violent fits of sneezing that they often occasion by the 

 irritation of the mucous membrane. The puparia are found, 

 like those of the ox-bot, beneath some shelter on the ground. 

 Many of the bots in the sinus cannot escape, and thus die. 

 On one occasion the author extracted from the cerebral hemi- 

 sphere a larva of the fly, it probably having entered through the 

 cribriform plate of the ethmoid bone. Sheep when suffering 

 from this pest shake their heads and wander restlessly about, 

 and present some of the symptoms of Sturdy. The disease for 

 this reason is called False-Gid, and can be told from true Gid 



