312 



• KNOWLEDGE ♦ 



[Oct. 17, 1884. 



summer and summer fruits. There, too, for the concep- 

 tioQB of advanced races are drawn from tl)e same sources, 

 the civilised peoples of Europe and America have placed 

 their heaven. And, save in refinement of detail incident 

 to intellectual growth, there is nothing to choose between 

 the earlier and the later ; the same gross delights, the same 

 earthborn ideas are there, whether we enter the Norseman's 

 Valhalla, the Moslem's Paradise, or the Christian's New 

 Jerusalem. 



PLEASANT HOURS WITH THE 

 MICROSCOPE. 



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



THERE is no class of animals which exhibit a more 

 curious variety of mouth organs than the insects, and 

 some of the most remarkable belong to the dipterous, or 

 two- winged grou]i, roughly known as flies. They all feed upon 

 ■fluid matter, but their habits are so different, as to require, 

 or to speak more philosophically, to result from, peculiar modi- 

 fications of the mandibles, maxilla', lips, tongues, &c. The 

 dipters are extremely numerous in species and individuals ; 

 many of them being the most annoying and mischievous 

 plagues. Of the whole lot it may be said that their two 

 •wings cannot be folded, and are accompanied at the base 

 by a pair of little expansions called alulets, and that they 

 have two poisers, filaments terminating in knobs, which 

 represent the lower or absent pair of wings, or at least are 

 generally thought to have that character. 



The divisions of insects into orders founded upon pecu- 

 liarities of their wings bring together species whose mouth 

 organs are strikingly different, and this is very conspicuous 

 amongst the dipters. A gnat, for example, is a pumper or 

 sucker, its mouth apparatus includes instruments for 

 making holes in its victims, and tubes to suck up their 

 blood. Common house-flies, bluebottles, and many others 

 are lickers or lappers ; and the most wonderfully provided 

 with a lapping tongue is, so far as the writer has seen, the 

 daddy-longlegs {Tijiula oleracea), grouped with the gnats 

 by entomologists. The bee is a lapping insect, but it does 

 its feeding work with a sweep of its mopping tongue, as was 

 explained in a former paper. The blow-flies, or bluebottles, 

 and flies more or less like it, lap in a different way. Fig. 1 

 shows in outline the horse's head sort of shape presented 

 by its proboscis when its two lobes are pressed together. 

 Fig. 2 shows them when they are opened to lap up a fluid, 

 as may be easily seen by putting one in the tubular live-box 



Fig. 2. 



xlescribed in a former paper, and supplying the creature 

 with a drop of honey, or syrup, or blood. The blow-fly 

 does not possess by any means the simplest form of this sort 

 of proboscis, but it is a good one to study, because the 

 insect is very common, and very ready to exhibit its mode 

 of using the instrument. 



A studetit will do well to mount one of these organs in 

 Canada balsam, after carefully washing it, but avoiding 

 opening and spreading out its two lobes. It should be well 

 ■examined in this position, which shows it to be supplied 



with a number of tubes, at first sight like the breathing 

 trachere, but the rings are not complete. There are gaps in 

 them which allow a fluid to enter. 



It is well worth while to buy one of Topping's beautiful 

 preparations of the blow-fly proboscis, with the lobes open 

 and extended. It is a work of gi-eat skill to produce any- 

 thing so perfect in its way, and the object is singularly 

 beautiful with dark-ground illumination. It is also desir- 

 able for the student to prepare slides with the lobes ex- 

 panded, and he will then see parts which Topping cuts 

 away to make others plainer. Each lobe has thirty 

 ])Seudotrachece, broad at their commencement, as they spring 

 from larger tubes, and getting gradually slender towards 

 their tips. No published drawings of the proboscis, in 

 accessible books, can be regarded as satisfactory. It would 

 take a clever artist a good whUe to make a good likeness, 

 and the engraving would be difficult to execute in a satis- 

 factory way. Fig. 3 shows portions of the pseudotrachefe 

 magnified about 500 times linear, and re])resented in plan. 

 In a perspective view the tubular character would appear. 

 Each pseudotrachea may be likened to a gutter, but the two 

 edges can be brought closer together when the two lobes are 

 in contact. 





Fig. 3. 



Common flies and bluebottles are omnivorous feeders 

 upon things that are either fluid or easily dissolved. If 

 they attack a bit of sugar, they can scrape it with teeth. 



When the proboscis is spread out with the lobes open, 

 these instruments are seen in the median line. Mr. Lowne, 

 in his book on " The Anatomy of the Blow-fly," says there 

 are from fifty to sixty of these bidentate tools, and Mr. 



