Mabch 1, 1899.] 



KNOWLEDGE 



49 



Founded by RICHARD A. PROCTOR. 

 LONDON: MAKCH 1, 1899. 



CONTENTS. 



Mosquitoes and Malaria. By Peect H. Gkimshaw, f.e.s. 

 Two Months on the Guadalquiver, — 11. The Marismas. 



Bv Habby F. Witheeby, f.z.s.. m.b.o.tt. (Illusfrate'l) 

 The Fluctuations of Rainfall. By AiEX. B. MacDowall. 



31. A. {lUttslraieJ) 

 The Mycetozoa. and some Questions which they 



Suggest. — II. By the Right Hon. Sir Ehwabd Fet, 



D.C.L., LL.D., r.R.s., and A&yBS Fby. 



Notices of Books 



Books Received 



Sunset on the Mare Crisium. By E. Walter Mauxdeb. 



r.E.A.S. {lUusfrated and Plate) 



The Planet Eros (D Q, 433) 



Letter: "Pbeplbxed" 



British Ornithological Notes. Comlacted by Habet F. 



WlTHEEBY, F.Z.S., M.B.O.TJ 



Science Notes 



Electricity as an Exact Science. — II. Units and 

 Measurements. By Howaed B. Little 



Triple Atmospheric Corona. By the Rev. Samtel 

 Bakbee. (Illi'.itrated) 



Mammoth Ivory. By R. Ltdekkee . 



Microscopy. By John H. Cooke, i.i.s., f.g.s. 



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



E.E.A.S 



The Face of the Sky for March. By A. Fowleb, 



F.E.A.S. - . 



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



PAGK 

 49 



51 

 54 



otj 

 58 

 fiO 



tiO 

 02 

 (32 



G:i 

 64 



64 



67 

 67 

 70 



71 

 71 



MOSQUITOES AND MALARIA. 



By Percy H. Gbimshaw, k.e.s., Natural History 

 Department, Edinhunjh Musetim of Science and Art. 



FOR some time past mosquitoes have been accused 

 of taking an important part in the dissemination 

 of certain diseases. This accusation was justified 

 some years ago by the researches of medical men 

 into the nature of the disease produced by a 

 parasitic worm known as the jilaria, or thread-worm, 

 various species of which are found beneath the human 

 skin, and which are quite common in hot countries. The 

 mosquitoes, in sucking the blood of an infected person, 

 are supposed to imbibe the parasites into their own system, 

 and then by dying, or in other ways, to contaminate water, 

 which may be afterwards drunk by some other person, to 

 whom the disease is thus commtmicated. Quite recently, 

 however, successful attempts have been made to connect 

 the " bite " of a mosquito directly with the production of 

 various forms of malaria, or malarial fever, as it should 

 more strictly be called. It seems that the medical experts 

 in London are now accepting the conclusions of Prof. 

 Grassi, of Piome, as to the cause of black-water fever, 

 which is one of the worst forms of malarial fever, and the 



scientific staff of the Natural History Museum, at South 

 Kensington, are inviting travellers in all countries to 

 collect as many mosquitoes as possible in the districts 

 visited by them, with a view to properly identifying the 

 various species, and tracing out still further the supposed 

 connection between these insects and some of the fevers 

 prevalent in tropical climes. 



In the transactions of the society known as the " Reale 

 Accademia del Lincei," published at Rome during the last 

 three months of 1898, Profs. Grassi and Bignami have 

 given a most interesting account of their experiments and 

 conclusions. As their commimications are in the Italian 

 language, and not generally accessible, it may be useful to • 

 give here a short resume of their researches. In order 

 to thoroughly imderstand the subject, however, my readers 

 must have a proper idea of the insects concerned, and also 

 of the nature of their so-called " bite." 



The name "mosquito" has from time to time been 

 applied to almost any small insect which sucks blood, but, 

 properly speaking, it only refers to members of one group 

 or family of two-winged tlies, that which contains the 

 true gnats. The latter name can therefore be applied with 

 absolute accuracy to mosquitoes. In this country we have 

 about twenty different species of gnat, in Europe there are 

 about fifty, and in the world generally over one hundred and 

 fifty. No doubt, with the increased attention which will 

 now be paid to this family of insects, many more species will 

 be discovered, although most people will be of the opinion 

 that we have a sufficient number already ! As I cannot 

 describe all the species without devoting a small volume 

 to them, and as they are all closely related to one another 

 in structure and habits, it must suffice to say a few words 

 about the best-known species, that bearing the name of 

 Culex pipiens. This is structurally a very beautiful insect, 

 about half an inch in length, which annoimoes its presence 

 by the peculiar " piping " sound to which it owes the second 

 part of its scientific name. It has only a single pair of 

 wings, thus proclaiming itself a true dipterous or " two- 

 winged " fly, six long, slender legs, a pair of feelers or 

 antennfE, and a proboscis which does all the harm. The 

 antennae differ greatly in the two sexes, for while in the 

 male they take the form of a pair of beautiful feathery 

 plumes, in the female they consist of a simple series of 

 joints each bearing a ring of short hairs. The sexes also 

 differ materially in the structure of their mouth-parts, and 

 it is important to note that only the female •' bites ' 

 or rather " punctures." The male is quite harmless 

 owing to the deficient nature of its mouth-organs, and it 

 is only necessary therefore to describe the proboscis of the 

 gentler (?) sex. 



Briefly, the proboscis of the mosquito consists of a tube, 

 or rather trough, within which are concealed no less than 

 six bristle-like boring implements, two of which are some- 

 what broadened and sharpened at the tip to form a pair of 

 small lancets, and other two barbed or serrated, so as to 

 form most effective saws. When the insect begins its 

 work it fastens the end of the trough firmly down against 

 the flesh of its victim. Then it places the bristles close 

 together so as to form a solid boring instrument, which it 

 plunges into the flesh and then sucks up the blood through 

 the tube which is formed by the union of the bristles with 

 the trough. 



Now, as mosquitoes are almost invariably found in damp 

 or marshy places, it is not surprising to learn that the 

 early stages of their life-history are aquatic. The female 

 insect lays about a couple of hundred eggs in a tiny boat- 

 shaped mass, which floats like a raft upon the surface of 

 ponds and stagnant water of all kinds. The eggs soon 

 hatch and produce grubs which live entirely in the water, 



