344 



SCIENCE- G OS SIP. 



MEETINGS OF MICROSCOPICAL SOCIETIES. 



Royal Microscopical Society, 20 Hanover Square, 



London. April 17, 8 p.m. 

 Quekett Microscopical Club, 20 Hanover Square, 



London. April 5, 19, 8 p.m. 



ANSWERS TO CORRESPONDENTS. 



F. L. (Sunderland). — The mite to which you 

 refer is Cheyletus eruditus. It is not a cheese- 

 mite, but belongs to an allied family, the Trombi- 

 diidae. An account of it can be found in Sgtence- 

 GOSSIP for 18fi9, page 5. It is tbere stated to feed 

 on cheese-mites and other acari. According to the 

 late Mr. Richard Beck, by whom it was first dis- 

 covered, parthenogenesis has been observed in this 

 species. 



W. W. (Clayton West). — I know nothing of the 

 microscope to which you refer other than the 

 advertisement. I recommend you to have nothing 

 to do with it. The twelfth immersion objective 

 alone, if good, would be worth £5. If you are 

 about to buy a microscope, go to a good maker, 

 and do not be persuaded into buying an inferior 

 instrument, such as is unfortunately too often disr 

 played for sale even in responsible opticians' 

 windows. If I can advise you on the matter I 

 shall be pleased to do so. 



EXTRACTS FROM POSTAL MICROSCOPICAL 

 SOCIETY'S NOTEBOOKS. 



[These extracts were commenced in the Septem- 

 ber number, at page 119 of the present volume. 

 Beyond necessary editorial revision, they are printed 

 as written by the various members. Correspond- 

 ence thereon will be welcomed.— Ed. Microscop}', 

 S.-G.] 



Development of Gnat. — My object in these 

 slides is to illustrate the transformation of an 

 insect, a subject I wish we saw more illustrations 

 of in our Society. Unfortunately, I am not able 

 to send a slide of the eggs of the gnat, but in 

 " Science for All " Mr. Hammond says that they 

 are laid in small boat-shaped masses which float 

 on the surface of the water. The eggs themselves 

 are of an oval form with a kind of knot at one end, 

 and are arranged side by side and closely packed 

 together. In Duncan's " Transformation of In- 

 sects " it is thus written : " The male gnats have 

 pretty hairy antennae, like little feathers, and the 

 females have antennae which are almost plain. It 

 is therefore not difficult to distinguish one from 

 the other, and it is rather important, for the 

 females are the blood-suckers. When about to 

 lay their eggs they seek the water, and with the 

 assistance of their long hind legs collect and agglu- 

 tinate them together and place the little boat-shaped 

 mass upon the surface of the water, and then leave 

 it to its fate.' - The larvae are soon hatched, and grow 

 with great rapidity. They are almost always seen 

 with their heads downwards and their tails towards 

 the surface of the water. After the larvae have 

 grown to a certain size they undergo a change of 

 skin and become nymphs or pupae, and it may be 

 noticed that when the nymphs come up to the 

 surface of the water they do not present their tails 

 like the larvae, so as to obtain air, but allow their 

 backs to touch the surface, just where there are 

 two respiratory tubes. "When the perfect insect is 

 about to emerge from the nymph stage it floats on 



the surface of the water, perfectly at rest, and the 

 skin of the back, which is exposed to the air, dries 

 and splits open. Then the perfectly-formed insect 

 begins to come out : first it protrudes its head, 

 then a portion of its body, and after a short time 

 one leg after the other is disengaged from the 

 nymph skin ; after a little while it tries its winys 

 and flies away. Fig. 1 shows the beautiful 

 breathing and swimming organs of the larva. 

 Fig. 2 shows the larva, and fig. 3 the pupa com- 

 plete, taken from Duncan. The pupa only shows 

 the respiratory tubes on its back. Fig. 4 repre- 

 sents the mouth organs of the female and fig. 5 of 

 the male gnat. It will be noticed that the female 

 gnat has no halteres. — T. G. Jefferys. 



The best account of the gnat known to me is that 

 given by Professor Miall in his " Natural History 

 of. Aquatic Insects," from which I make the follow- 

 ing excerpts : " Small stagnant pools and ditches 

 are the favourite haunts of the larvae and pupae 

 of the gnat. A ditch in a wood choked with fallen 

 leaves is one of the best hunting-grounds, and in 

 the summer months they may be found by the 

 thousand in such places. The larva, when at rest, 



Fig. 1. Breathing and Swimming Organs of Larva 

 of Gnat. 



floats at the surface of the water. Its head, which 

 is provided with vibratile organs suitable for sweep- 

 ing minute particles into the mouth, is directed 

 downwards, and, when examined by a lens in a 

 good light, appears to be bordered below by a 

 gleaming band. There are no thoracic limbs ; the 

 hind limbs, which are long and hooked in the 

 chironomous larvae, and reduced to a hook-bearing 

 sucker in Simiilmm, now disappear altogether; a 

 new and peculiar organ is developed from the 

 eighth segment of the abdomen. This is a cylin- 

 drical respiratory syphon, traversed by two large 

 air-holes, which are continued along the entire 

 length of the body to supply every part with air. 

 The larva ordinarily rests in such a position that 

 the tip of the respiratory syphon is flush with the 

 surface of the water, and thus suspended it feeds 

 incessantly, breathing uninterruptedly at the same 

 time." Professor Miall's explanation as to how it 

 is possible for a larva heavier than water to remain 

 floating at the surface without effort, as the larva 

 of the gnat appears to do, is too long to give here. 

 It deals with the surface film. " After three or 

 four months the larvae are ready for pupation. 

 By this time the organs of the future flv are almost 



