• 43 



tributed to the extremities of the body, from which it returns through irregular channels 

 (there being no special vessels for its conveyance), to the dorsal cavity. 



Below the heart and occupying the median line of the body is the alimentary canal 

 which may be divided into four parts the gullet, the crop, the stomach, and the in- 

 testine ; each having a special structure and appendages, which it is not possible to sat- 

 isfactorily describe here. 



Under this, along the floor of the body is located the nervous column, which, how- 

 ever, on entering the head splits into two branches which embrace the gullet, and knit 

 together above it, expanding into a bilobed ganglion, or brain, from which nerves are 

 distributed to the different organs of the head. In the thorax is situated another large 

 ganglion, supplying the appendages of that segment, while in the abdomen smaller 

 ganglia are found from which ramifications extend in every direction. 



The respiratory system is also a complicated one, and differs more in its arrange- 

 ment from the analogous organs of higher animals, than do the circulatory, nutritive 

 and nervous systems. Along the under surface of the body are placed several pairs of 

 minute breathing orifices, called stigmata or spiracles, protected from the intrusion of 

 solid particles by an intricate network of five ramifying filaments proceeding from the 

 circumference. Through these spiracles the air enters into lateral trachae or air tubes, 

 from which it is conveyed by smaller branches which ramify to all parts, and to all 

 organs of the body. By means of these minute air-vessels the blood is oxygenized as it 

 forces its way between them in returning to the dorsal cavity. The fly has also two 

 capacious air-sacs or pouches in the base of the abdomen, and according to some authors, 

 two much smaller ones in the front of the head. 



The foregoing is but a meagre outline of the structure and organs of the house- 

 fly, of which the more closely we study its anatomy, either in the larval or perfect 

 state, the more are we struck by the admirable adaptation of its structure to its mode 

 of life. 



A much disputed point in connection with the house-fly is whether it has the habit 

 and ability to bite persons, as some other flies do. Perhaps the great majority of people 

 would answer in the affirmative, and conscientiously attest that they had themselves 

 been so bitten. From the formation of the fly's proboscis, with its feebly developed 

 mandibles, it hardly seems probable that the skin could be punctured. Yet the authors 

 of the little book already mentioned (Earth-worm and House-fly) after microscopic ex- 

 amination and description state that the lancets, representing the maxillas and mandi- 

 bles, " are employed to puncture the objects from which the fly sucks the juices, " and 

 are the weapons that annoy us. However this may be, it appears that the culprit who 

 thus assails us, especially during showery weather and late in the season is a distinct 

 species, although it so closely resembles M. domestica as to deceive all but entomologists 

 familiar with these insects. Its name is Stomoxys Calcitrans, and it is distinguished by 

 its long horny beak, which, as pointed out by De Geer, has a long and very sharp lancet 

 sliding in a groove, while the fleshy sucking discs at the extremity of the proboscis 

 are small and inconspicuous as compared with those of the house-fly. There is also a 

 slight, but perceptible difference in the wings, and in the position in which they are 

 held by the insect. 



One naturally associates the house-fly with the habitations of man, but it is not con- 

 fined to them, but extends its range over the whole country, and may be found almost 

 universally distributed, and prepared to welcome the first human visitor to any locality. 

 In the May number of " Psyche" appeared a short article by a Collector in the far 

 West, showing that even in the secluded canons of the Eocky Mountains the newly 

 pitched tents would soon become disagreeably filled with flies, chiefly and unmistakably 

 M. domestica. As the article gives an interesting account of the manner in which flies 

 are sometimes destroyed by wasps, I will quote a portion of it. 



" While camping in Santa Fe Canon, N. Mexico, in August, 1880, this plague of 

 flies seemed about to be unusually formidable. On the very first night the lower sur- 

 faces of the roofs and ridge-poles of the tents were fairly blackened by the immense 

 multitudes of dipterous pests. The next morning it was observed, somewhat to the 

 alarm of the women and children of the party, that large numbers of so-called yellow- 



