INSECTS. 189 



which time they alter their shape in various ways. 

 Those just born are white, one- twenty-fifth of an inch 

 long, while those which have reached the length of two- 

 fifths of an inch are yellowish white. Individuals 

 ready to become pupae are about an inch long, yellowish 

 brown, with dark transverse lines ; they wander back 

 to the nasal cavities and thence to the exterior, often 

 being expelled by sneezing. In the soil they become 

 pupas, first of a brown, then of a black colour, within 

 the larval skin ; the flies emerge in six or seven weeks. 

 Different maggots develop at different rates, accord- 

 ing to the nature of the cavities into which they 

 penetrate. 



The maggots cause the disease known as "false 

 gid," which appears most obviously from March to 

 May; at this time the parasites are tolerably well 

 developed. They irritate the mucous membrane of 

 the cavities of the head in which they live, causing an 

 unusually large flow of blood to these parts, as a result 

 of which the mucus secreted in the nose increases 

 largely in quantity (sneezing, snuffling), and the brain 

 begins to work abnormally (uneasy movements of the 

 head, high lifting of the feet ; in worse cases, rolling 

 of the eyes, gnashing of the teeth, and foaming at the 

 mouth). The sheep have also an intolerable itching of 

 the nose, which they rub in consequence on the ground, 

 against posts, or their own legs; besides this, there 

 may be inflammation of the eyelids and increased 

 secretion of tears. They are also apt to grow very 

 thin. The disease is more frequent, and the symptoms 

 severer, in young than in old sheep. False gid may 

 cause death ; the animal is cured, however, after the 

 maggots have crept out. Preventive Measures : Keep- 

 ing the sheep away from the edges of woods, avenues, 

 etc., where the flies live by preference. When sheep 

 are killed, the maggots coming from the head should 

 be collected and destroyed. Smearing the margins of 

 the nostrils with tar, or rubbing them with walnut 



