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 
larvee 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 without legs. 
When full grown they fall through the nostrils of the sheep 
and change to pupz 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. Itisa 
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; but 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. (8) 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. I 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 is almost a certainty that, perhaps, ten per cent. of the 
offspring 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 
