Adc. 3, 1883.] 



♦ KNOWLEDGE ♦ 



71 



PLEASANT HOURS WITH THE 

 MICROSCOPE. 



By Henry J. Slack, F.G.S., F.R.M.S. 



IT is very common for persons unacquainted with en- 

 tomology to suppose all the flies of somewhat similar 

 aspect seen on a window-pane are the same sort ; the big 

 ones being taken for the grandfathers and grandmothers, 

 and the least for their baby grandchildren. All insects, 

 however, that pass through transformations such as common 

 flies and butterflies do, reach their full size when they 

 emerge from the chrysalis, and do not grow afterwards. 

 Another common mistake is often made towards autumn, 

 when " the flies " are accused of biting, the words implying 

 a belief that the common house-fly gets vicious, or goes 

 mad about that time of the year, which is not the case. 

 Everybody must have noticed that when a house-fly settles 

 upon any substance to feed, it puts forth a horse's head- 

 like proboscis. This is a most wonderful apparatus, and 

 a good way of commencing acquaintance with it is to assist 

 at a bluebottle's dinner. To accomplish this, tirst catch 

 your bluebottle and keep him under a pill-box or a wine- 

 glass till his meal is ready. To prepare it, crush a bit of 

 loaf sugar the size of a pin's head in a droplet of water. 

 Take a little of the syrup thus made upon the end of a bit 

 of wood — a lucifer match is just the thing — and smear it 

 on the inner side of the glass cover of the live-box opticians 

 usually supply with a microscope. Put the bluebottle 

 upon it, and quickly shut him up by pressing the live-box 

 into the rim of its cover, leaving the fly no room to turn 

 over, but not squeezing him. The box is then placed on 

 the microscope stage and the fly has his under side upper- 

 most. It will soon begin to suck the syrup. The proboscis 

 comes ovit of a cavernous cleft, the horse's-head end 

 of it opens like two lips, which press against the glass, 

 and the fluid is rapidly swallowed. If it is too thick, 

 the fly can moisten and thin it. It can only swallow 

 fluids, and the wonderful collection of tubes kept 

 open by series of incomplete rings of a hard material 

 act as filters to keep solid particles out. It would take a 

 volume to describe the details of this wonderful apparatus, 

 and no drawings can be made efiicient substitutes for seeing 

 the thing itself. The student should dissect such oVijects 

 with needles set in wooden handles, fine scissors, and a fine, 

 thin-bladed knife. It is also well to buy two slides made 

 !)y a skilful preparer ; one with the proboscis flattened 

 out in the common way, and another mounted in fluid, and 

 not squeezed out of its true shape. The insects can be fed 

 with syrup tinged with cochineal, and the motion of it 

 better seen. No examination of the house-fly or blow-fly 

 will detect any apparatus adapted for biting or piercing 

 a hard substance. In the middle of the proboscis are some 

 teeth fit for scraping a material like moistened sugar, but 

 no saws or lancets, or even knives capable of cutting. 



On a hot day in the country, especially near cattle or 

 horses, flies something like bluebottles and house-flies, 

 but with elegantly-mottled wings and splendid green and 

 bronze eyes, are sure to be found. These will take any 

 opportunity of exercising their skill upon the hands or 

 faces of human beings. They are furnished with a pro- 

 boscis similar to that of the house-fly or bluebottle, and 

 use it in the sam(! way, but their delight is to suck the 

 blood of the animal th(!y torment, and to get at it they 

 have tools to pierce a tough skin. If one of these flies is 

 iiold in the hand by the wings, and the proboscis is gently 

 poked with a finger-tip, some sharp tools will come out of 

 a fold in its upper side. The males have four, and the 

 females six implements. The latter will be found to 



possess a pair of Fig. 1, and another pair of Fig. 2, and 

 one each of Figs. 3 and i, which are pressed together to 

 form a tube. A power of about 25 linear, obtained 

 with an inch and a-half objective, will show the bluebottle 

 at his dinner, and be sufiicient to exhibit the form of the 

 knives, &c.,of the breeze-fly. A much higher magnification, 

 say 500 linear, shows that an instrument (Fig. Irt), shaped 

 like a carving-knife, or sword-bayonet, has its edge very 

 fine and sharp, and the back, for more than half its length, 

 very finely serrated, with the teeth set downwards. As 

 it is pulled back out of a wound it would both enlarge and 

 irritate it. The next tool (Fig. 2a) has teeth much like 

 those of a coarse rasp, such as is used upon wood. This 

 can act quickly upon the-hides of an animal, and the great 

 central tubular organ has teeth at the top, which a move- 

 ment of partial rotation backwards and forwards must 

 make a good piercer like a drill. 



liMmimiiliify^ m{ji},^ I §i liijijji 



Fig. la, X 500. 



Fig. 3a, X 500. 



All these instruments should be teased out with needles, 

 and mounted in Canada Balsam. A fly's head, with these 

 organs simply extended, should also be kept as an opaque 

 object. Unfortunately the splendid eyes do not retain 

 their colour, but while fresh are singularly beautiful when 

 strongly illuminated. 



To see the bluebottle using his proboscis or trunk, it 

 must be lit up from above. A Lieberkuhn acts well, or a 

 side silver reflector. Beck's is an excellent pattern ; but 

 th(! ordinary form answers well, and best if it is mounted 

 on its own sliding stand and not made to fix on the micro- 

 scope. Few spectacles are more astonishing than the quick 

 nervous agitation with which the great lips open and shut, 

 and the vigour with which they work. 



