September 1, 1891.] 



KNOWLEDGE. 



16? 



boldt, who was a firm believer in the poisonous nature of 

 the bite, considered this sucking out of the poison to be 

 the explanation of the painlessness of some wounds. His 

 experience was almost the reverse of that of Mr. Dimmock, 

 as detaUed above. He affirmed that if the insect were 

 allowed to suck to satiety no swelling took place, and no 

 pain was left behind, and considered that when pain was 

 produced it resulted from the hasty interruption of the 

 process of sucking, since then the last infused poison would 

 not be able to be withdrawn. He experimented with one 

 of the most virulent species, allowing it gently to settle on 

 the back of his hand, and reports of it : "I observed that 

 the pain, though violent in the beginning, diminishes in 

 proportion as the insect continues to suck, and ceases 

 altogether when it voluntarily flies away." The following 

 experiment, however, seems to throw some doubt on the 

 poison theory altogether. He says : " I wounded my skin 

 with a pin, and rubbed the pricks with bruised Mosquitos, 

 and no swelling ensued." On the whole, therefore, it must 

 be admitted that great difliculties beset both of the two hypo- 

 theses that have been commonly advocated in explanation 

 of the swelling and pain consequent on the bite. Of course 

 similar remarks would apply in the case of both bugs and 

 fleas. 



There seem to be chiefly two species of true Gnats that 

 infest houses in this country, which are named Cul^'.l■ 

 tinnuldtits and ciliaris. The former has pretty spotted 

 wings, but must not be confounded with another spotted- 

 winged Gnat-like fly (Fig. 4) which is frequently found in 

 windows, and is generally called 

 the " window Gnat " {Bhyplms 

 fenesti-dlU). The specific name 

 fen est ml is (from Latin fenfstr<t, 

 a window) was given to it in 

 consequence of its usual habit 

 of flitting about windows. It 

 belongs, however, to a different 

 family, and its habits and life- 

 history are totally unlike those 

 of the true ' 'ulices. Its larva 

 is terrestrial, not aquatic, and 

 lives in dung. Culex ciliaris, 

 specially known as the " House 

 (inat," is a reddish - brown 

 insect, mth greyish wings. 



The Culices, or true Gnats 

 and Mosquitos, ai'e not the only 

 " thread-horned " flies that 

 trouble mankind by sucking 

 blood, though they are usually 

 the chief; it is diflicult, how- 

 ever, to give definite popular 

 names for the other species. 

 The word " Midge " is perhaps most connnonly used as 

 a general term for them, though it is also employed 

 for insects of similar structure but of less annoying habits. 

 To the genera Sitnulium and ('I'nitiijKKinn belong some of 

 the most annoying of these persecuting Midges, and some 

 of the former become occasionally almost as bad a plague 

 as the Mosquitos proper. The Sinnilia are also known as 

 " sand flies," and in America, where they have occasioned 

 great annoyance and trouble amongst the cattle, they are 

 called "Turkey Gnats" and "Buffalo Gnats." They are 

 small, dark-coloured insects, of a less fragile nature than 

 the Culicfs, but still " thread-horned," and not therefore 

 to bo confounded with any of the " short-horns," such as 

 the great, stout-bodied " breeze-flies," which are also 

 terribly bad stingers. The flies have the peculiar habit of 

 emerging from the chrysalis beneath the surface of the 



Fio. 4. — Window Gnat 

 (Rhiiphus fenesfralisj. 



water. The Ceratopor/on, which is sometimes troublesome 

 in this country, is a minute grejnsh-brown insect ; it is 

 sometimes abundant in marshes and fens, where the 

 females are very annoying. 



But besides these, many other insects are eaUed Midges, 

 though they are not troublesome. There are, for example, 

 first, the Cliironomi or Plumed Gnats, the larvfe of one 

 species of which are the grotesquely wriggling red, worm- 

 like creatures, found in ponds and water-butts, and called 

 " blood-worms." These are more uniformly cylindrical 

 than the larvae of the Culices, and besides wriggling about 

 in the water, they construct amongst the mud at the 

 bottom, tubes composed of particles of decayed leaves, 

 fastened together with silken threads. The pupa, which 

 is similar in shape to that of the Culices:, and has an 

 enormous fore-part, may be distinguished by the pair of 

 exquisite white plume-like tufts that project from the sides 

 of that part of the body. Each consists of five hairs, 

 which are delicately fringed, so that the whole makes a 

 large rosette. The pupa usually lies at the bottom 

 helplessly, though it can swim, if obliged ; a few hours 

 before becoming a perfect insect it mounts to the surface 

 to prepare for the change. The perfect insects are called 

 " Plumed Gnats," because of their beautiful antennse, 

 which are even more deeply feathered than those of the 

 Culicen. They have no long beak, and are not adorned 

 with scales like the true Gnats. These Chironomi form in 

 the air dancing swarms which usually consist chiefly of 

 males. Then there are the " Winter Midges " (Tridweera) 

 which form little hovering swarms on bright days during 

 winter and spring. These again are quite different fi'om 

 the Gnats, and belong to the daddy-longlegs group. The 

 last " Midges " to which we shall refer are the family 

 called Pxijchidiihr, most exquisite, though minute creatures 

 (Fig. 5), some of which are commonly found in houses, 

 on the walls, or running in little 

 zigzags up and down the windows. 

 They too are " thread-horns," but 

 can be easily distinguished from 

 the others by the peculiar shape 

 and adornment of the wings. 

 These are lancet-shaped, and are 

 thickly covered with hairs, often 

 so distributed as to form a pretty 

 pattern, and this, coupled with the 

 fact that they rest with wings not 

 crossed over their backs as Gnats 

 do, but spread out and sloping backwards at their sides, 

 causes them to look like tiny moths. They are harmless 

 little creatures, and their larviB live in dimg. 



Fig. 5. — Midge 

 (Psi/choda). 



THE MINERALOGY OF METEORITES. 



l)y \ AiGHAN Cornish, B.Sc, F.C.S. 



AT various times and places, solid bodies of either a 

 metallic or a stony character have been observed 

 to fall from the sky, the occurrence, fi-om circum- 

 stances of time and place, having evidently no 

 connection with volcanic eruptions. 

 These bodies, termed Meteorites, possess peculiarities of 

 mineral composition and structure which alone would 

 serve to place them in a class apart from the ordinary 

 rocks of the earth's surface. There are, however, differences 

 of character among Meteorites themselves ; which are for 

 convenience classed as — 



Sideritos, Siderolites, Aerolites, 



according as they are composed principaDy of metallic 

 constituents (iron alloyed with nickel), of metallic and 



