Septemher, 1902. T 



KNOWLEDGE 



193 



Founded by RICHARD A. PROCTOR. 

 Vol. XXV.] LONDOS : SEPTEMBER. 1902. [No. 203. 



CONTENTS. 



Insect Oddities. I. Bv E. A. Butleh, B.A.,B.st. (lUustraleil) 



The Air over London. By tlu> Rev. John M. B.vcoy. 



{IlluslrateJ) ' 



The Number of Moults undergone by Dragon-Fly 

 Nymphs. By tlie Kev. AKTiirR E.\ST {Illustrated) ... 



Euphratean Divisions of the Circle. By Rubkht 

 BkmW.v, .IiNit., F.s. A. {Illii.'itrated) 



Astronomy without a Telescope. XVII. — Stars by 

 Daylight: and the Sum of Starlight. By E. 



WaITEK llArXDKB, F.K.A.S. 



The "Triple Cave" in Aquila. By ])r. Max Woi.f. 



<,PU'I<') 



Letters : 



Visibility of the Cbescext of Venus. By J. AV. 



Mkahes 

 The Si'i'PO.-iED Discovery of Aluminium 2000 Years 

 Aoo. By JoBN T. Kemp 

 British Ornithological Notes. Conducted by W. P. 



i'YCK.VFT, A.LS., F.Z.8., M.B.O.U. 



Notes 



Notices of Books 



Hook.-* Ri:ikivi:u 



Arctic Oceanography 



Studies in the British Flora. V.— On an Irish Bog. 



By R. I.i.OYD Praegeb, b.a. 

 Collecting, Preserving and Mounting Algae. By IIexbv J. 



Foster .. 

 Microscopy. Conducted by M. I. Ceoss. {Illustrated) ... 

 Notes on Comets and Meteors. By W. F. Denning, 



F.R.A.S. ... 



The Face of the Sky for September. By W. 



Shacxleton, p.e.a.3. ... 

 Chess Column. By C. D. Locock, b.a 



PASK 



193 



203 

 203 



203 

 204 

 205 

 207 

 207 



211 

 213 



215 

 215 



INSECT ODDITIES.-T. 



By E. A. Butler, b.a., b.sc. 



While hardly any great division of the animal kingdom 

 is devoid of species that exhibit fantastic and outlandish 

 forms, the class Insecta is jierhaps furnished with more 

 than its fair share of these. We have already discussed 

 in these papers some few of these extravagances of form, 

 especially in the development of the limbs, and some good 

 reason was generally found to be assignable for tlie 

 quuintness of structure they exhibited. But even in the 

 cotnpuratively limited fauna of the British Islands, there 

 are plenty of others which exhibit an equal, or even 

 greater, bizarrerie, for which it is less easy to find an ade- 

 quate reason. It may safely be affirmed that the order 

 Khynchota, or bugs and frog-hoppers, is more productive 

 thau any other group of the extraordinary forms to which 

 we allude, and it may not be without interest to direct 

 attention to a few of these oddities, which, although some- 

 times not of the commonest occurrence, will yet hardly 



fail to strike the observer when he does happen to mi'i^t 

 with them. 



The first that calls for notice is a little creature of such 

 weird aspect that one can scarcely be surprised at its 

 having been associated by country folk with the powers of 

 darkness. Its scientific name is Cenlroiua cornidus, and 

 amongst the peasantry of France, its dark colour combined 

 with the sinister appearance of its fore-parts has gained 

 for it the sobriquet " Le Petit Biahle," while an English 

 author speaks of it and its relatives as "Fiend-Flies," 

 and an American entomologist describes them as 

 " Brownie-bugs." Cenlrotus is not a very large insect, 

 being only about f of an inch long, and, moreover, it belies 

 its a.ppearance by being perfectly harmless. When viewed 

 in front (Fig. 1, a) it seems to show a brownish black 



Fro. 1. — A, Front view of Face and Prothorax of Cenlrotus 

 cornutus. B, Side view. 



vertical face surmounted by a pair of curved horns, and 

 this was quite enough in raediajval days to suggest a 

 Satanic association. But it is not really the head to 

 which this formidable appearance is due. The head in 

 fact is neither very large nor conspicuous save for the 

 rather large and wicked-looking eyes ; but the prothorax 

 has taken on the most grotesque form, rising perpendicu- 

 larly above the head, surmounting it as with a head-dress. 

 This head-dress nms out into the aforesaid horns at the 

 side, while between them there is a little ridge which, if 

 we follow it backward, we see gradually extending and 

 enlarging till it forms a long sword-like appendage 

 (Fig. 1, b) reaching nearly to the end of the body, and 

 looking like a sort of stiff puggaree to the aforesaid head- 

 gear. 



There is nothing retnarkable about the rest of the insect. 

 It has four ordinary membranous glassy-looking wings 

 with distinct nervures, the upper pair being stouter than 

 the lower, and its legs and body are quite normal in shape. 

 It is simply this extraordinary development of the thorax 

 that makes it such a wild and odd-looking being. It is 

 impossible to say whether this quaintness of form has any 

 bearing upon the insect's present mode of life, or is in 

 any wav in correspondence with its usual environment. 

 It is an inhabitant of woods, living amongst the herbage, 

 chiefly in our southern counties, but too little is known of 

 its habits for it to be possible to give any adequate 

 explanation of its form. It belongs to one of those orders 

 of insects which do not undergo any very great change of 

 form during the course of their life, and which never jiass 

 iulo the C|uiescent stage of neither taking food nor moving 

 about — in other words, its metamorphosis is of the kind 

 known as " incomplete." The young insect is shaped 

 something like the adult, but of course has no wings, and 

 the thoracic horns and tail do not attain their characteristic 

 form till the last moult. It is a vegetarian in diet, sucking 

 the juices of plants through a short beak, and is therefore 

 probably mild and inoffensive in its ways, so that the only 

 use one can suggest for its curious armature is that it 

 should act as a terror-producing signal upon any would-be 

 assailant. 



In other parts of the world, other species are found, 

 more or less closely allied to this, in which the thorax 



