308 THE ENTOMOLOGIST. 



increase in size the upper surface becomes marked with two 

 brown lines on each segment, the anterior being shorter and 

 narrower than the posterior; and some spots are also observ- 

 able on the sides : they consist, as usual, of twelve segments 

 besides the head. When placed on a rough surface these 

 larvae crawl with considerable activity, first fixing themselves 

 by two jaw-like hooks, with which the head is furnished, and 

 thus drawing up the body, which is quite w^ithout legs. 

 When full grown they fall through the nostrils of the sheep 

 and change to pupae on the ground among the herbage, and, 

 not unfrequently, attached to a blade of grass : in two 

 months the pupa-case splits open and the perfect fly comes 

 out. Sheep are exceedingly annoyed by these flies, and to 

 escape them will often be seen lying down in cart-ruts with 

 their heads close to the ground; at other times we see them 

 huddled together in a dense crowd under a tree, each having 

 its head turned towards the trunk of the tree and its nose 

 pushed into the wool of the one standing before it. It is a 

 very general opinion that the operations of this insect, being 

 carried on so near the brain, cause that vertigo, or giddiness, 

 so well known as a serious and most fatal disease ; bat my 

 friend Mr. Reeks, who has had great experience, doubts this 

 conclusion, and gives the following reasons for his incre- 

 dulity : — "(1) Young sheep go ' giddy' at all seasons of the 

 year until they are about eighteen months old, but mostly so 

 in the dead of winter, no matter how severe and frosty 

 the weather may be. (2) A giddy sheep never recovers; but 

 would most assuredly die if not killed. (3) Giddiness is 

 transmitted through several generations by sheep in the same 

 flock, which have not, however, been affected. (4) Giddiness 

 will invariably arise from continued interbreeding, and is 

 very similar to the imbecility in the human species by 

 continued intermarrying. 1 will give you a case in point: — 

 Supposing a farmer has four hundred ewes, which have bred 

 lambs this year from lambs (rams), which were their own 

 offspring last year : this will not cause giddiness; but if they 

 (the rams) are used next year with their sisters, so to speak, 

 it i*s almost a certainty that, perhaps, ten per cent, of the 

 off'spring of these young ewes will go giddy ; and if the 

 process of interbreeding be continued for another year, or so, 

 it will take several generations to get giddiness out of the 



