268 DIPTERA. 



the ground, buries itself, and transforms to a pupa. 

 Fig. 217, 3, is the puparium from which the fly has 

 escaped. 



The larvae of different species of bot-flies off'er many 

 modifications of structure. Those living within cuta- 

 neous tumors of mammals have fleshy tubercles for 

 mouth parts, instead of hooks like the species inhabit- 

 ing the head and stomach. The horse bot-fly, Gas- 

 trophilus equi, lays its eggs on the hairs about the 

 knees of horses, often on the inside. Five hundred 

 or more may be laid on one horse. The eggs when 

 deposited contain the larvae in a more or less per- 

 fectly developed state, so that they hatch in a few 

 days. The young (and also the eggs frequently) are 

 transferred by the horse, when licking its own skin, 

 to the mouth, and from thence they pass to the 

 stomach and intestines. Here they fasten themselves 

 by their hooked mouth parts, and remain for nine or 

 ten months. If they are very numerous they create 

 a dangerous irritation, from which the animal may 

 suff'er great agony and finally perish. In other cases 

 they are ejected in the excrement, and pass the pupa 

 state of from forty to fifty days in the earth.^ 



PULICID^. 



The family PuHcidae is regarded by some entomolo- 

 gists as a distinct order under the name of Siphonap- 

 tera and Aphaniptera ; by others it is placed among 

 the Diptera. Specimens of fleas can often be col- 



1 See A. E. Verrill, " The External and Internal Parasites of 

 Man and Domestic Animals," Rep. Conn, Board ^^., 1870. 



