156 CUERENT NOTES. 



still further pollute it. The observations upon Cyclops, as far as they go, 

 also point in the same direction/^ The screening of water-tubs, tanks, etc., 

 in the vicinity of houses, so as to prevent mosquitoes from laying eggs therein, 

 may therefore be regarded as an unmixed benefit, and should be rigidly 

 enforced by the proper authorities in all malarial centres. 



In the June number of 'Science' (1910, i, p. 869), Dr. Frederick Knab 

 rightly emphasises the importance of ascertaining precisely the habits of any 

 given species of mosquito before money is expended on its destruction. On 

 the littoral of Tropical America two species, Culex extricator and Deinocerites 

 sp., breed abundantly and exclusively in crab-holes. It has been suggested 

 that measures should be taken to exterminate their larvae, and to this 

 Dr. Knab takes exception, on the ground that there is no evidence that either 

 species ever enters human habitations, and further that no signs of blood 

 could be found in the females of the Culex which had been examined. What- 

 ever may prove to be the truth in this particular instance, it is well to 

 remember that although the number of mosquitoes now known to inhabit 

 Africa is very considerable, yet there are very few of which we can say, with 

 any degree of certainty, that they feed on the blood of man or domesticated 

 animals. More precise records with regard to this important point are much 

 to be desired. 



In the same article Dr. Knab contests the supposition that the yellow-fever 

 mosquito i^Stegomyia fasciata, F.) lays its eggs actually on the surface of the 

 water. He states that " the eggs are deposited out of the water, at the edge 

 of the water film ; here the eggs remain until they are submerged, when they 

 promptly hatch. Eggs remaining out of the water retain their vitality for a 

 long time. In laboratory experiments eggs have been kept dry as long as 

 five months and, when then submerged, produced larvae ; under favourable 

 conditions out-of-doors it is to be supposed that they will survive even longer." 

 These interesting observations may account to some extent for the wide dis- 

 persal of Ihis dangerous pest ; for the prolonged vitality of the eggs and the 

 situations in which they are laid render it probable that they might 

 occasionally be carried for considerable distances adhering to the feet of 

 water-birds. 



Some two years ago an attempt was made to introduce into Algeria, from 

 Louisiana, a colonj^ of the fossorial wasp, Monedula Carolina. These wasps 

 feed principally upon Tabanid^e (variously known as horse-flies, hippo-flies, 

 seroots, etc.), and it was hoped that they might prove effective in reducing 

 the numbers of those species of Tahanus which are probably responsible for 

 the dissemination of the trypanosomiasis of camels. The insects were exported 

 in the pupal stage, the pupae being kept in cold storage to check their emer- 

 gence. A number of them survived the ordeal and were placed out in 



