322 DIPTERA. 
flightly, 'and said, that I should hereafter 
read a full account of it. 
Mother, Yes, my dear Lucy ; and 
when I think you can understand the 
minute description that has been given of 
the wonderful structure of that cater- 
pillar, you shall read it, and have the 
plates to examine. 
The horns of these rat-tailed larvse — 
Lucy, Why rat-tailed, mamma ? 
3Iother, Because their shape has some 
resemblance to a rat's tail, which you 
know is very long and slender. These 
horns quickly grow to a considerable 
length, and answer the same purpose as 
the tail did before transformation, and as 
the stigraatae do when the insect has as- 
sumed its perfect state. 
Lucy. The animal then breathes 
through these horns ? 
Mother. It does ; they are spiracula, 
or breathing passages; and, in about 
twenty-four hours after they have at- 
tained their proper length, the fly is 
