31 



the same insect deposits eggs three or four times during her short life, which lasts only a 

 few weeks. 



Assuming that the fly deposits eighty eggs at one sitting, and that she does this three 

 or four times during her life, and knowing that the progeny in a very short time become 

 parents themselves, it has been calculated that a single female might in one season, pro- 

 vided all her progeny survived, become the parent of upwards of two millions of flies. 

 Here then we have a basis of calculation sufficient to account for the greatest increase we 

 have ever witnessed, for, presuming that but comparatively few of our summer torment- 

 grs find hiding places sufiiciently warm and sheltered to winter in, they would be quite 

 numerous enough, taking into account their natural rate of increase, to stock our houses 

 by midsummer. It is also quite probable that millions of eggs which are laid in the fall 

 pass through the rigours of winter unharmed, and hatching out by the warmth of the sun 

 in early spiing, add greatly to the numbers of those who have survived in the perfect state. 



In summer the eggs are hatched in a few days after being deposited, into long white 

 maggots or larvae. The body of a larva is divided into thirteen rings or segments. The 

 anterior one, or head, being furnished with a pair of hooked jaws, and rudimentary eyes. 

 These are the only external organs ; the creature is perfectly smooth and without feet. 

 While in this state it is constantly devouring the substances in which it was hatched, and 

 rapidly increases in size, and in a few days assumes the pupa or chrysalis state. This 

 change is eff'ected by the hardening of the outer skin, which becomes brown and tough, 

 forming a little barrel shaped case, very much resembling a grain of rice in the husk. 

 While the insect is in this second stage it is undergoing those remarkable changes, both 

 internal and external, which raise it from the type of a worm to that of a highly organized 

 insect. These metamorphoses are soon completed, when the fly forces its way out of its 

 prison house in the following manner : — By a series of muscular eff'orts it detaches itself 

 from the pupal covering, and then strikes its head repeatedly against one end of the case un- 

 til it bursts open as it were upon a hinge, when the fly emerges; at this stage the fly presents 

 an odd appearance, being full grown and perfect, with the exception of the wings, which 

 are soft and flabby, aud not more than one-fourth their natural size. However this im- 

 perfection is soon remedied, as the wings reach their prop.^r size and hardness in a few 

 minutes, and the active little creature flies away to bask in the sunshine with his fellows, 

 or to join them in sipping the delicacies of our tables whenever they come within reach. 



Having now briefly gone over the history of our Musca domestica, we will glance at a 

 few of the most important and interesting features in its structure. Common and insig- 

 nificant as we regard the house fly, it is a creature of most delicate and intricate organi- 

 zation, furnishing examples of delicacy of structure, and adaptation of means to ends, be- 

 fore which the highest skill of man falls as comparatively nothing. In the case of our 

 house fly, the microscope has proved invaluable ; it has shown in the structure and ap- 

 pearance of those parts which we will briefly attempt to describe, and has enabled the 

 skilful naturalist to observe how the insect performs many of its functions. 



First of all, the proboscis or tongue claims our attention. We give a magnified repre- 

 sentation of that organ in fig. 24, along with other parts of the mouth. 



The maxillse are minute ; their palpi, m p, being single-joint- 

 ed, and the mandibles, m, are comparatively useless,' being verj 

 short and small compared with the lancet like jaws of the mos- 

 quito. But the tongue itself, or the labium (/) as it is called, is the 

 most curious piece of mechanism. It consists of a tubular bag, 

 formed of thin transparent membrane, dilated at its extremity, 

 where it forms a large sucking disc. This disc is divided into two 

 broad flat muscular leaves, which present a sucker like surface. 

 These leaves are supported on a framework of modifled trachea, 

 which end in hairs projecting externally. The whole tongue is so 

 constructed as to gather the fluids to which it is applied, and pass 

 them to an aperture in the centre which leads to the throat or gul- 

 let. On the under surface of this sucking disc are a number of 

 ribs reseiuoiiag tubes sliced lengthwise, the open portions of which face downwards, 

 forming passages for the liquid food. It will be observed that these ribs are distributed 

 with great beauty and regularity, and most of them empty themselves into four main 



