January 2, 1899.] 



KNOWLEDGE 



19 



Fig. 1. — Ovipositor of Beetle 

 (Baptolinns alferiians), x about 

 40 diameters. 



in South Hampstead, on the edge of some turf, and I 

 captured the male— which is precisely like the female 

 externally — in a similar spot in a garden in Southwold, 

 Suffolk. 



THE TEETH OF THE DUNG FLY. 



Four years ago I mounted the head of a fly, which 

 showed a process of teeth at the end of the proboscis ; I 

 paid little attention to the subject tUl Mr. Pillischer, of 

 New Bond Street, showed me a slide, which he informed 



me had been in his possession 

 for thirty years, and con- 

 sidered unique, of the teeth 

 of a fly. I had, some little 

 time previously, mounted a 

 whole insect, showing the 

 teeth, which Mr. Austen, of 

 the British Museum, at once 

 identified as ScatopJiaija ster- 

 eo rari a, and this being a very 

 common insect, I had no 

 difficulty in obtaining speci- 

 mens. I find that Mr. W. H. 

 Harris has figured and pub- 

 lished an account of the teeth, 

 in the Proceedings of the 



Cardiff Naturalists' Society, so late as July, 1898, and 



earlier in Science Gossip, in 1885. 



Prof. Packard, in his introduction to " Entomology," 



also refers to the teeth of the 

 house-fly as being placed 

 between the roots of the 

 false tracherc, but the tooth 

 figured there has no resem- 

 blance to those of the dung 

 fly. These are placed at the 

 base of the labellum of the 

 proboscis, and appear not to 

 be between the roots of the 

 false tracheff, but to cover 

 them : are of a very tooth- 

 like appearance, chitinous, 

 and stand out well coloured, 

 making a nice object for 

 microscopic examination, 



with a sixth of an inch power. 



Scatophaga is a predaceous fly, and is decidedly raptorial 



in appearance. It may be seen sitting on leaf, the head 



well raised on the forelegs, 



and the body sloped at an 



angle to its support, watch- 

 ing for smaller flies. A 



species of ScKtoiise is the 



smallest, and the house 



fly {Musca doniestica) the 



largest I have seen cap- 

 tured, the blue-bottle 



{Liicilid f;ffi.s«r) being beyond 



its powers. It does not 



hunt, but waits till its prey 



is within an inch, or an 



inch and a half, when it 



is seized with a rapid 



sprmg. The wings of its 



prey are then compressed 



with the hind legs, which 



are tarnished with many 



strong spines, or spurs, to assist that operation. The 



thorax is held with the forelegs, which have a perfect 



clievaux-de-frise of setffi on the end of the tibia, as well 



Fig. 2.— Teeth ot Fly {Scato- 

 phaga stercoraria), x abDut 150 

 diameters. 



Fig. 3. — Proboscis, Laueets, and 

 Maxillary Palpi of Dung Fly 

 {Scatophaga stercoraria), x about 

 25 diameters, shon-ing the position 

 of the teeth. 



Fig. i. — Clasper of .^. stereo- 

 raria, x 75 diameters. 



segments quite broken up. 



as other setse, arranged in very much the same way as 

 those on the hind leg of the worker honey bee {Apis 

 melinca]. With the prey thus firmly held, the Scatophaga 

 inserts its lancets into the membrane between the head 

 and the thorax, and the tragedy is completed. 



I had an opportunity on several occasions of verifying 



an observation of Prof. Packard's, that the true voice of the 

 house fly is a sound produced through the spiracles of the 



thorax, and not by a hum of 

 the wings. When an unfor- 

 tunate fly was seized and so 

 firmly held by the Scolophaga 

 as to be incapable of move- 

 ment, I heard a pecuhar, 

 characteristic, shrill sound 

 proceeding from it. The teeth 

 obviously play an important 

 part in these struggles, as they 

 must be of great use in tear- 

 ing and scraping the harder 

 parts, to enable the trachea 

 to suck the juices — indeed, I 

 have fouad the abdomen of a 

 Scatopse SO treated, and the 

 The dung fly also sucks some 



secretions of plants, as I have many times seen it busy 



with its proboscis on the viscid disc of the ivy blossom, 



though its presence there may be not wholly for such an 



innocent purpose, as these blossoms are much resorted to 



by other flies. 



It has been said that, contrary to the rule in most 



insects, the male of Scatophaga 



is larger than the female. I 



have had several species under 



observation, S. stercoraria. S. 



lutaria, S. merdnria, and I 



cannot endorse this, as I found 



a great variability in size, 



some males, apparently of the 



same species, being a third 



larger than others, and the 



same with the females, and I 



have watched a small male 



mate with a large female, and ^ „ , r^ 



vice versa. The males are t, ^^.'^•/'rf' 1- ^ , 



. ■ , 3 i , , 1 ,. 7, Tai-si ot tore lee ot S. stereo- 



furnished at the end of the .^ria. showing spines used in 



abdomen with two powerful holding prey, x 150 diameters. 



clasping hooks, which are 



fitted with sharp hairs, arranged like a comb on the inner 

 concave edge. This insect is therefore remarkably 

 specialized in many ways for the " struggle for existence." 

 It ought perhaps to be mentioned that the drawings 

 are made from microscope slides, the objects being mounted 

 under pressure, and consequently somewhat altered in 

 shape. 



*- 



ELECTRICITY AS AN EXACT SCIENCE. 



By Howard B. Little. 



I. — Tradition, Mysticism, and the Early Pl-rsuit 

 OF Truth. 



TRADITION, even that tradition which clings, 

 limpet-like to the adamantine sheath of a 

 science, is, in one respect at least, like antique 

 furniture. If, in the existing generation, the 

 supply be not equal to the demand, then some 

 enterprising ehUd of the period wiU undertake its manu- 

 facture. This is to be regretted, because the poetry of a 



