652 H. M. WOODCOCK. 



Until the beginning of June I had the same difficulty there. 

 As soon, however, as the regular summer weather set in — a 

 moist, sweltering warmth — there was no difficulty in getting 

 the Culex to bite (once, at any rate). It must be re- 

 membered that all the research done o;i Culex hitherto, in 

 this connection, from which it is known both to transmit 

 certain haematozoa and to harbour flagellates (which in many 

 cases are most probably hasraoflagellates), has been done in 

 countries where a much higher average summer temperature 

 is experienced than in England. And I do not think that I 

 succeeded in getting sufficiently favourable environmental 

 conditions in my laborator}' attempts in London. 



There is another probably equally essential point, of which 

 I was not aware at the time of my (the above) experiments. 

 According to Mr. E. H. Ross, in a report on the prevention 

 of fever on the Suez Canal (Cairo : National Printing Depart- 

 ment, 1909),^ the mosquitoes (females) apparently desire to 

 suck blood only after having been fertilised. As it happened, 

 in my early work I kept the bred-out females separate fi"om 

 the males, of which I took no account, thinking they were 

 not required (as, of course, they do not take blood). Hence 

 those females used were certainly not fertilised. As regards 

 the caught "wild" ones, however, it is just as likely that 

 they were fertilised as not, so that some of these ought to 

 have bitten, had other conditions been suitable.- 



Another Possible In sec tan Host. — Owing to my lack 

 of success in this essential preliminary, I was left in the dark 

 as to whether Culex was the alternate host of the Hajmatozoa 

 of the chaffinch or not. I may point out in passing that a 

 study of the cultural forms of the Trypauosome which I have 



1 See ' Nature/ vol. Ixxix, 1909. 



" In working at Rovigno, wliei-e I was able to breed out the Culex 

 in greater abundance. I left the two sexes together, for the sake of con- 

 venience in dealing with the insects. In this case many females were 

 fei-tilised, for I frequently noticed the little " egg-rafts " floating on the 

 dishes of water in the cage. Probably those females which sucked 

 blood had been fertilised. 



