April 1, 1890.] 



KNOWLEDGE 



103 



,^-^,'^KT T t' ^^ M'® Vised as aids 



^< il wV J-^ J J f I ^*\« accompanying dri 



^^^ AN ILLUSTRATED ^^ -—^r^^Z^ 



individual nervures being identified and named, so as to 



in classification. A comparison of the 



■awing of a bluebottle's ■ning (Fig. 2) with 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: APRIL 1, 1890. 



CONTENTS. 



House-flies and Bluebottles. — II. By E. A. Butler ... 103 

 Hindu Aritlimetic. By Frederic Piscott. M.E.A.S. ... 105 



Walks in the Sydney Botanic Gardens. By C. 



Pakkinson. F.G.S 107 



Flying Dragons. By U. Lydekkek, B.A.Cantab 109 



The Bamboo and its Kindred. By R. Camper Day. 



B.A.Oxon. Ill 



Notices of Books 113 



Letters: — Asaimi Hall, Georije Knott. Robt. W. D. 



CnuisTiE. J. Shaw, J. F. King. " y Dracoxls" ... 117 



The Face of the Sky for April. By Herbert 



Sadler, F.R.A.S 119 



Whist Column. By W. Montagu Gattie 120 



Chess Column. By I. Gunsbebg 122 



HOUSE-FLIES AND BLUEBOTTLES.-II. 



By E. a. Butler. 



AS all five of the Hies mentioned in our last paper 

 belong to a single family, the Miisciihe, they 

 exemplify the same structural type, and, except in 

 a few matters of detail, one may be taken as 

 representing all. To illustrate the main points 

 in a fly's structure, therefore, we will select the bluebottle 

 or blow-fly (' iiUiiilinnt). as it is the largest of the indoor 

 species, and can always be easily obtained, ^^'e will sup- 

 pose that we have before us one of these flies, which has 

 been killed without crushing or otherwise damaging the 

 body ; this can be done by means of the fumes of chloro- 

 form, cyanide of potassium, or crushed laurel leaves, any 

 of which will in a few moments render such an insect in- 

 sensible, while a longer exposure to the poisonous vapours 

 will kill it entirely, and leave it in a good condition for 

 examination. 



The distinguishing feature of the order is at once 

 noticed in the single pair of membranous wings placed 

 horizontally over the back when at rest, and extended at 

 right angles to the body when in use. .\s the Diptera are 

 the only order of insects in which a single pair of wings 

 is normally present, there is very little dilHculty in distin- 

 guishing them, and there are very few other insects that 

 can possibly be mistaken for them. Each wing consists 

 of a thin double nu-mbrane, strengthened by six longitu- 

 dinal hollow ribs or " nervures," of which tlie larger con- 

 tain breathing tubes (trachea^) and nerves. The nervures 

 are not scattered at random, but always, as in other orders, 

 follow a definite course, which varies somewhat in difi'erent 

 genera or even species, but is constant in tlie same, and 

 the general plan is sufiiciently definite to permit of the 



Fig. 2. — Wing of Bluebottle {Calliphora). 



those of the larger and smaller house-flies given in our 

 last number, will further show what sort of differences may 

 be expected in this respect. The present plan is very much 

 like that of the house-fly proper, and the chief difference 

 is in the prsebracliial nervure (the third on the disc of the 

 wing towards the tip) ; in the present species it will be 

 found first to bend at right angles towards the ner\-ure 

 above it, and then to slope towards the margin, while the 

 little cross nervure (discal transverse) which joins it to the 

 next below, meets it very much nearer its upward bend 

 than in Mimm damestirn. The front edge of the wing is 

 bounded by the strongest of all the nervures, the costal, 

 which is furnished, towards the base, with a row of short 

 bristles. To the naked eye the wing appears to consist 

 only of membrane and to have no clothing of any kind ; 

 but miorcscopic exammatiou shows a multitude of ex- 

 tremely muiute hairs distributed all over its siu-tace, but 

 very evenly and regularly disposed. There are also larger 

 hairs on the nervures, which may perhaps be sensory in 

 function. 



The wmgs can be vibrated with marvellous rapidity, 

 sufficiently so to produce a recognisable musical note. 

 Attempts have been made to determine the number of 

 vibrations per second by observing the pitch of the note. 

 The usual pitch of a fly's hum is some\\liere about the 

 notes E or F, and the corresponding number of vibrations 

 would be something between 320 and 330. The charac- 

 teristic liu^diuj of our bluebottle, however, is not due to the 

 vibration of the wmgs, nor, like the shrill song of the 

 grasshopper, or the squeak of the water-beetle, to the fric- 

 tion of one part of the body against another ; for Laudois 

 discovered that the thorax of a bluebottle continued to buzz 

 with scarcely diminished vigour after the separation of the 

 wings, legs, head, and abdomen. There is also a large 

 and beautiful yellow-banded fly. called Scriconii/iii baiYdlix, 

 not uncommon in our mountainous districts, which has by 

 several observers been noticed to '• shig " whilst at rex't. 

 The Rev. .1. Hellins, of Exeter, thus writes of it in Dec. 

 1881 : " One day during the past autumn I went with a 

 small party for a walk on Dartmoor, near Okehaiupton ; 

 after some miles of rough tramp up and down several tors, 

 as the afternoon was drawing on, we found ourselves on a 

 heap of stones on the top of Cawsand, and were glad to 

 rest there awhile ; before long, a piping sound was audible, 

 and one of the party said the wind was whistling ; but to 

 this explanation I demurred, having some recollection of 

 having heard the noise before ; so. looking round, I soon 

 saw several large flies resting on the stones, and was j/.e- 

 sently able to convince my friend that the sound came ft-om 

 them." In the case of the bluebottle, at least, and also 

 probably in that of the other fly as well, the sound-. 



