December 29, 1923] 



NA TURE 



935 



after A. costalis and the hibernation problem had 

 been settled, my assistant and I while searching a 

 marsh near Port Louis were astonished to find a 

 larva of A. funestus. Further search in this marsh 

 demonstrated that A. funestus was here in large 

 numbers. The fact that A. funestus had not been 

 recorded from INlauritius before, in spite of the work 

 of the previous investigators, coupled with the 

 proximity of the marsh to Port Louis — where all 

 ships enter Mauritius — led me to assume that the 

 species had only recently been imported. I immedi- 

 ately approached the Officer Administering the 

 Government for authority and funds to abolish this 

 marsh ; and by the copious use of paraffin castor-oil 

 mixture, while hundreds of men tore up the weeds, 

 by drainage and filling-in operations, within a few 

 days the marsh was changed into dry land. 



Control of all the nearby waters — fortunately few 

 — was instituted, and no larva appeared in these 

 waters. A few days later, while I was in conversation 

 with one of the chief moustiquiers (mosquito searchers) 

 — an Indian who had been trained by Ross and 

 Fowler — this man told me that he thought he re- 

 membered having seen similar larvae while Ross was 

 in the island, at Schonfeld Marsh, Riviere du Rempart 

 in the north. 



I questioned him further, pomting out that it was 

 difficult to remember the appearance of larvae after 

 the lapse of 15 years ; but he seemed so certain 

 that I despatched him to Schonfeld to search. 

 Schonfeld ]\larsh is rather inaccessible, some 15 miles 

 from the marsh at Port Louis, and as the man had 

 to go on foot it was two days later before he returned. 



\\'heii he got back, however, he brought with him 

 six lar\<r of A. funestus. My assistant and I at once 

 left ior Sclionfeld Marsh in my motor-car, taking the 

 man witli us, and after searching for two hours in 

 .this extensive marsh, I discovered a larva of A. 



not it.-, there for myself. 



On my return to Port Louis, I issued instructions 



at all moustiquiers should divide up and proceed 

 t< " ; .Its of the island and search only for A. 

 'if! Tuo weeks later, A. funestus had been 



re})onc. I uoin practically every district of Mauritius, 

 but tlic luiinbers found were surprisingly few. 



I tluii decided personally to undertake the study 

 of the l)ionomics of the species, and I at last found — 

 as 1 have fully described in my report — that A. 

 funestus existed in Alauritius in prodigious numbers, 

 in sonic localities actually outnumbering A. costalis. 

 failure to discover the larvae in numbers before 

 to the fact that the vibrations transmitted 

 tlic ciiili hv till' tread (if the searchers warn 

 i>f (lan,<j;cr, and they all dart to the roots 

 Moil, to which they cling, or even climb 

 (/> till- dainf surfaces of the leaves which 

 [dip iuL(^ the water. ()inc thi- fa- t h.-nl been (lis- 



vercfl, thousands of . I , /'.- /-< I, ■, ^ 1 <iiil<l aKva\'S 

 (; had in snit.dilc i 



I In "■■ Miission 



: i uKicuitputpis 111 tlie island, and 



iiiicr species could very easily be 



f. nu'irtilifalfi'; could also be 



' ii (liirKiillv. Conscciuently, 



'-- '1 i>' > ■■■ '■•■ '•' '—"Iriria 



1 nndcrl 

 Iby A. inr 

 pound tl; 

 infected, . 

 infected 

 instead c 

 in Maui 

 .;. msln! 



w 11 

 I 



to aCCOinil !oi 



( 1 ill. I i. / 



/"/// ill .M.Miii: 



that 11 \'.a^ <)iil\ liic ini|)(jrtati 

 of llidiaiis to v\ork III the 

 briii'Mii- Willi liieiii ill their i)l()od tlie parasites of 



NO. 282(>, VOL. 112 1 



malaria, that caused the extensive infection of the 

 local anophelines. 



(2) That prior to 1865, when the first considerable 

 outbreak of malaria (?) occurred, no anopheline 

 vector existed in the island, and that it was only 

 by accidental importation of A. costalis (A. funestus 

 and A. maculipalpis?) then that Mauritius became 

 malarious. 



Personally I am inclined to favour the first theory, 

 but the following experience shows how impossible 

 it is to be dogmatic. 



Towards the end of my work in Mauritius, hearing 

 that the sister island of Rodrigues was free of malaria, 

 I obtained sanction from the Officer Administering 

 the Government to proceed to Rodrigues in order to 

 investigate this report. 



The island is so small that it was possible, with 

 the assistance of three skilled helpers, to search all 

 the streams, marshes, and pools. No Anopheles were 

 to be found, and no case of malaria acquired in 

 Rodrigues existed, although on the other hand I was 

 able to find persons with all three species of the 

 malaria plasmodia in their blood, which they had 

 acquired by former residence in Mauritius. 



The island of Rodrigues lies 365 miles to the east 

 of Mauritius, and is visited regularly, though only 

 every 3-4 months, by the Government supply steamer 

 from Mauritius. On this ship, which is berthed 

 in Port Louis, A. costalis was found even during 

 my voyage, and it seems obvious that the only thing 

 that accounts for the fact that Anophelines have 

 not been introduced into Rodrigues is that the island 

 is completely surrounded by an extensive and remark- 

 able coral reef, running from 1^-6 miles seaward, 

 which forces all vessels to anchor at least i^ miles 

 from shore. Moreover, a steady wind from the south 

 almost invariably blows across the island from the 

 shore across the anchorage. 



In my report I have described these investigations 

 at length, but I am in the meantime asking Sir 

 Ronald Ross if he will be good enough to add any 

 remarks he may care to make on what these investiga- 

 tions have shown. Malcofm 1". M.vcGregor. 



Wellcome Field Laboratory, Wisley, Surrey 

 (Wellcome Bureau of Scientific Research). 



Tni:st.: investigations appear to me to be both 



theoreiiealU' and practically important. The (|uestioii 

 is whether ./. funestus entered Mauritius after my 

 visit in m»o.s. Major C. E. P. Fowler and my- 

 self were m the island from November 20, 1907, 

 until February 25, 1908, that is, during the summer. 

 Of course, we could not make anything like a com- 

 plete sur\c\' 1^^ tlie mosquitoes in that tinu\ imt we 

 were gi\eii the assistance of Mr. I )'haiiniere/ do 

 C'harino\ , tin- aciomplislicd entomologist of the 

 island and (uiator of the museum, and were also 

 provided with ten " inoiisti(|uiers," tliat is, ♦■■••■••r-i 

 mosquito men. ()ur ]inneipal investi.ijat r 

 niado riose to theCdairtond Marshal l'h(eni\ ..,,,> a 

 was drainecl in uioH ; but Major h'l.wler and Mr. 

 I » hanniere/, imcsti^ateil nuuh further afield than 

 this. li IS theiidoie must suriuisinu th.it we did 

 iidi (in..- ..111!.- ,1. i..-.> /. ,',,■/;. ■/;f^. 1 remember that 

 w I;, ! 1 he isl.ind 1 exjiei ted 



1. I - : 111 lit 1\', p. lit 1\- hei ause 



had liiiiiid lliem 111 ,!,s>. mi.i 1 10:1 m Siena I ,eone 

 'lere indeed we h.id dl^el i\i-i e. 1 and named A. 

 I'stus), and also because we heard that both 

 ■ squitoes aboundeil m the nei;_;hbourin,i:; island of 

 Mlagascar. It seemed surprising to nie (hit only 

 of these Madagascar Anopheles had mini -id to 

 drift into Mauritius. Moreover, we he.u.l that it 



