Dkckmber. U)U. 



Kxo\VLi:i)Gi:. 



475 



and detached elements. 



and the anterior and posterolateral ones are missing, so that 

 there are no secondary canals ; the posterior lateral sclerite 

 is very large, and there are only six or seven canals, each with 

 a very few supporting sclerites, 

 which have prominent squared 

 ends and very thin curved backs ; 

 each of these seems to be in 

 reality compound. So distinct 

 is the type of proboscis that 

 there can be no doubt whether 

 a fly belongs to that group or 

 not ; and the same may be said 

 of Scatopliaga, of the different 

 Syrphids, and probably of any 

 genus of the Hrachycera. 

 Dipterists, of course, have other 

 characters to guide them, but 

 these other characters arc also 

 concerned with modifications of 

 the chitinous parts, so that the 

 microscope may be of use in 

 supplying additional characters. 

 A good deal may be seen of the 

 working of the proboscis in the 

 living tiy ; but there are certainly 

 some points in its action not yet 

 clearly made out. The pure 

 microscopist knows the blow-fly's 

 tongue as a test object ; but the 

 tongue of the house-fly is really 

 better for this purpose, as the 

 supporting sclerites of the canals 

 are relatively less spirally twisted, 

 and consequently more distinct. 

 Viewed on the open side they 

 look like a row of arrows and 

 croquet mallets placed alternate- 

 ly, side by side ; we must imagine 

 the letter C, to which they have 

 been compared above, to have 

 its lower limb split, forming a 

 small V. When one looks over 

 the tongues of a number of 

 different species, a great number 

 of variations on this pattern are 

 found ; indeed the canal sclerite 

 of a fly seems to be as charac- 

 teristic as the spicule of a 

 sponge. We also notice that 

 the type used in the canals of 

 some species is used in the 

 supporting parts of others ; and 

 hairs may also be found of such 

 a form and distribution as to 

 suggest that all these objects, 

 even the " teeth," are in reality 

 modified hairs. 



It is of some importance to the 

 microscopist to be assured that 

 his test object is of the species 

 named; I have seen the .proboscis 

 of Eristcilis labelled " Tongue 

 of blow-fly"; these Syrphids 

 have the intercostal distances of 

 the canal-supports often less 

 than one micron, so that their 

 resolution forms a test of a 

 different order. In the Cordy- 

 luridae the distances are also 

 short, but owing to the flattened 

 form of the sclerites resolution is 

 much easier. The preparation 

 of these organs is not a difficult 

 matter. Yon may soak the fly's 

 head in caustic potash or other 

 alkali to dissolve the muscles, 



I'll. I I i "I. L\illif>liori! voiintoria, anterior end 

 of central basal region of suctorial pad. The scleritic 

 junction with the anterior basal canal is seen to be 

 composed of twinned sclerites of similar pattern. The 

 bodies of the teeth are seen, though their points are 

 not in focus. It will be observed that the sclerites of 

 the canals simulate a spiral, but are really separate 



300. 



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■•::-.. -v-. \% V'JPi 7 >•..-::.•••• ...•■•;:::■ 



•'»i;v "►>*. ^^- 



Figure 502. Musca domestical anterior part of 

 suctorial pad, showing anterior basal row of sclerites 

 of each side, with the secondarj' canals derived from 

 them. Some of their sclerites are focused for the back 

 of the " C," and appear as transverse lines ; others for 

 the open front, showing a varying pattern of angles or 

 curves. In the membrane itself there are a few small 

 circles, looking like the roots of hairs ; these appear to 

 have a sensory function. X 300. 



afterwards washing it and bringing it into acetic acid for 

 the actual dissection. A much easier plan, which I find 

 more satisfactory, is to take a dried specimen, remove 

 the organ with the point of a pin 

 (this may often be done without 

 damaging the remainder of the 

 fly), and put it into a drop of 

 strong acetic acid, which will 

 soften it in a few minutes or 

 hours as the case may be. Next 

 remove as much of the acetic 

 acid as possible by means of 

 blotting paper, and substitute a 

 drop of good creasote. This will 

 clear and dehydrate, and dis- 

 section may be performed in 

 this medium very easily. In 

 order to show the suctorial pad 

 I detach it from the rest of the 

 tongue, so that it is freed from 

 the intrinsic muscles and the 

 external surface with its hairs. 

 This little operation can best 

 be managed by insinuating the 

 point of the needle behind the 

 posterior transverse sclerite. The 

 suctorial surface thus freed 

 consists only of integument, and 

 can be induced to lie flat much 

 more easily. The creasote is then 

 removed and the object mounted 

 flat in a drop of diluted balsam. 

 The integument is pliable so long 

 as it remains in creasote ; it 

 stiffens at once in the presence 

 of xylol. Other specimens may 

 advantageously be made, show- 

 ing the entire organ in different 

 attitudes. 



I'he figures are from photo- 

 graphs taken with Graetzin in- 

 candescent gas burner, Kohler 

 lens-system, aplanatic condenser, 

 sixteen millimetres apochromat, 

 and eighteen millimetres com- 

 pensating ocular, all by Zeiss, 

 llford Process plates were used, 

 and Imperial Process developer; 

 the exposure (according to the 

 equation) in the case of Figure 

 501 was seventy seconds. A 

 longer exposure was tried for the 

 next illustration (Figure 502) 

 at one hundred and twenty 

 seconds, when fine results were 

 obtained, and the thinner and 

 sharper lines thus produced 

 show well in the reproduction. 

 My equation was based upon a 

 large number of experiments made 

 with a more rapid developer ; 

 this present one is slower, but 

 gives much more detail, is quite 

 clean in working, and certainly 

 the most useful for this purpose 

 that I have yet tried. The full 

 aperture of the objective was 

 used, the condenser iris being set 

 only to exclude extraneous light. 



E. W. BOWELL. 



THE ROYAL MICROSCOP- 

 ICAL SOCIETY.— A conversa- 

 zione was held at King's College, 

 Strand, on Wednesday, October 

 15th, the President and Mrs. H. 

 G. Plimmer receiving the guests. 



// 





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