242 



Marvels of the Universe 



Hholo Inl] 



It:. J. tiirilta. 



THE GRUB OF A FLY. 



This much enlarged pholo of the "maggot" which iscues from the Fly's 

 egg shows the true form. The mouth is at the pointed end and the 

 digestive tract is shown as 



of a horny substance closely resembling 

 chitin. In the mammal air is taken 

 in by the mouth, and after being led 

 through tubes (the bronchial tubes), 

 enters the lungs, which may be de- 

 scribed as consisting of an abundance 

 of little sacs, capable of opening and 

 closing, about which the small blood- 

 vessels encircle. The air, in passing 

 through these air-sacs, re-oxidizes the 

 blood in the adjacent blood-vessels by 

 simple contact, and thus purification 

 of that fluid is effected. In insects, 

 however, the arrangement is modified. 

 Holes in the sides of the body of the 

 insect or between some of its segments 

 darker band. (called splraclcs) exist, which lead into 



tubes that pass in all directions, and are all of different sizes, throughout the entire body. The 

 blood, however, is not contained in an}' vessels, but is loose, and circulates freely all about the 

 contents of the sac, and playing over these air-tubes, wherever they may be, causes re-oxidation of 

 that fluid. The spiracles, or little holes, are more highly developed and easier seen in the Water 

 Beetle than in the case of the Fly. One of these spiracles was given in an earlier page to show 

 how Nature adopts an ingenious method for keeping out dirt or any foreign matter from the 

 tubes by stretching across the entrance numerous twig-like little branches, closely associated 

 together, and which act as a kind of mechanical filter. The tubes from these holes, which pass 

 throughout the body in all directions, are beautifully made, consisting of(,spirally wound fibres, the 

 spirals themselves (figure of 8 in form in the large tubes) being designed to be of a somewhat spring- 

 like nature, so as to assist in the distribution of the air as the insect draws in and lets out its breath. 

 We have never seen the result of any experiments for ascertaining the rapidity of breathing in 

 the case of the House Fly, but in that of the Bee it has been estimated at about forty when at rest, 

 but when pushed, to reach from one hundred and ten to one hundred and sixty times a minute. 



It is not improbable the breathing of 

 the Fly is much the same. 



The egg-laying apparatus of the Fly 

 (called the ovipositor) is a curiously- 

 shaped arrangement, the object of the 

 different parts not being accurately 

 known. It is somewhat long and 

 stout, being especially made for the 

 purpose of pushing aside bits of straw, 

 etc., as the insect deposits its eggs 

 deep down in the warm parts of a 

 heap of stable manure. Here they 

 hatch. On this page is shown the egg 

 of a House Fly, whilst on the opposite 

 page is a group of eggs which, although 

 often sold as those of the House Fly, 

 are really derived from some other 

 species. The eggs of the Stable Fly 



Photo by] 



{E. J. ^JHlUl, 



EGG OF HOUSE-FLY. MAGNIFIED. 



The egg is very long in proportion to its width, and quite devoid of 

 ornamentation. It hatches in t\%'enty-four hours, producing a maggot like 

 that shown above. 



