41 



detect the culprit when he pilfers from your sugar bowl, or commits an assault upon your 

 person. 



The body of the fly consists of three sections, named respectively the Head, Thorax 

 and Abdomen. 



The head bears a pair of large, semicircular compound eyes, each having about 

 4,000 hexagonal facets, each of which lenses corresponds to a single eye, being isolated 

 from the adjacent ones by a dark pigment, and being connected with the optic nerve. 

 There are also three simple eyes or ocelli, arranged in the form of a triangle upon the top 

 of the head, between the compound eyes. Thus liberally endowed with organs of sight, 

 the fly sees in almost every direction without change of position, and by their aid often 

 escapes an untimely end. From the front of the head spring the antennaB, which are 

 short, being composed apparently of only three joints, but really of six : the third is 

 dilated and much larger than the others, while the fourth, fifth and sixth form a kind of 

 plume. When the insect is at rest the antennae are folded down at the base of the probos- 

 cis, so as to be nearly hidden from sight. 



The mouth parts are, however the most curious and interest- 

 ing structures of the head, being modified from the biting or 

 gnawing mandibles of the larva into an organ capable only of 

 sucking up liquids. (See fig. 55). In this proboscis the hard 

 parts, such as the lancets of other flies, are almost obsolete. 

 The maxilla and single-jointed palpi are small, and the short 

 mandibles are of little use, leaving only a fleshy, tongue-like or- 

 gan, which is bent up under the head when not in use. This 

 tongue, or labium, consists of a tubular bag, formed of thin, trans- 

 parent membrane, dilated at its extremity into a large sucking 

 disk. This expansion is divided into two broad muscular leaves, 

 supported upon a frame-work of modified trachae, and present- 

 ing a sucker-like surface, with which liquids are lapped up. The 

 modified trachae which sustains the expanded sucking-disk end externally in projecting 

 hairs, and they give to the fleshy disc the properties of a minute rasp, which is employed 

 by the fly in scraping or tearing delicate surfaces. As Newport states : — " It is by this 

 means that it teases us in the heat of summer when it alights on the hand or face, to sip 

 the perspiration as it exudes from and is condensed upon the skin." With this organ the 

 fly also tastes and sips the delicacies of our tables, for, with the maggots grovelling form, 

 he seems also to a great extent to abandon the lowly and depraved tastes of his youth, 

 and searches thenceforth for sweets and dainties, the pursuit of which often proves fatal 

 to him. 



The proboscis of the fly is also fitted for other and more dangerons services, as 

 shown by Dr. Thomas Taylor in a paper, (read before the Montreal Meeting of the A. A. 

 A. S.), on the " House-fly as a Carrier of Contagion." While engaged in dissecting the 

 head of a common house-fly, he noticed emerging from the ruptured proboscis a very 

 minute snake-like animal — a species of anguillula — measuring about eight one hundredths 

 of an inch in length by two one thousandths of an inch ia diameter. Subsequent exam- 

 ination proved the sucking-tube of the proboscis to be of sufficient diameter to admit of 

 taking up spores of cryptogams, eggs of trichinae and anguillulae, or even the latter ani- 

 mals themselves ; thirteen of these having been found in the proboscis of a single fly. 



These facts suggested to Dr. Taylor the importance of ascertaining, by experiments, 

 whether flies might not be carriers and distributors of noxious germs. To test the ques- 

 tion practically, he placed in a large glass receiver several hundred house-flies and a 

 quantity of the spores of the red rusts of grasses, (Tricholoma) with the following results: 



11 The flies at first did not seem to esteem the spores as suitable food, but, on the 

 morning of the third day I found that the rust was replaced by larvae and remains of eggs 

 of the common house fly. The eggs were deposited and hatched between Saturday noon 

 and the following Monday morning, 9 o'clock, or in about forty-eight hours. On the 

 following day I placed in the receiver about a quarter of an ounce of the same descrip- 

 tion of spores, combined with sugar. The flies partook of this confection, consuming the 

 sugar and most of the spores. In about twenty-four hours after the flies had partak e 



