174 



previously. Two hundred other laboratory- bred flies were allowed 

 to feed on a healthy horse and records were kept of the mortality in both 

 cases, with the result that in the first ten days twice as many of the 

 filaria-fed flies died as of the controls. After ten days, the mortality 

 among both sets of flies was practically the same. In the gut contents 

 of one fly, fed on infected blood, a filaria was found in the act of being 

 ingested by a polymorphonuclear leucocyte ; this may possibly 

 explain the non-development of many embryos ingested by the flies. 

 Dissections of 31 flies from the fifth to the eighth day after a meal of 

 infected blood, showed in these cases larval worms embedded in the 

 muscles of the thorax. After the eighth day, no evidence of parasite 

 invasion could be discovered. The five horses were kept in screened 

 stables throughout the experiments and though examination of the 

 blood of the four healthy animals was made two or three times weekly 

 for 60 days after the last feeding by the infected flies and again a 

 month later, no evidence of infection could be discovered. 



BisHOPP (F. C). A Point to be considered in Utilizing the Duck as a 

 Mosquito Destroyer. — Amer. Jl. Trop. Med. & Prev. Dis., New 

 Orleans, ii, no. 12, June 1915, pp. 767-768. 



There is a point, in connection with the habits of ducks, particularly 

 when kept rather closely confined, which under certain circumstances 

 may somewhat detract from their value as mosquito destroyers [see 

 this Review, Ser. B, iii, p. 25]. Where they are confined in yards of 

 which the ground is rather moist, they often dig holes — sometimes to 

 a depth of from 4 to 6 inches. These holes form admirable breeding 

 places for mosquitos and are frequently bidden by a partial or 

 complete covering of grass. 



Hewitt (C. Gordon). The House-Fly. — Cambridge University Press, 

 1914, 382 pp., 3 coloured plates, 101 figs. Price 155. net. 



There is no insect which has had so much written concerning it in 

 the last ten or fifteen years as Musca domeUica. It shares with the 

 mosquito the honour of being the greatest insect enemy of mankind, 

 and accounts of its structure, life- history and habits with their con- 

 sequences to man, now require a volume of some size. The 

 anatomy of the insect and larva is minutely described and fully 

 illustrated ; its general habits and bionomics are stated in detail, 

 and in discussing the question of the mode of hibernation, the 

 author appears to consider that it can scarcely be doubted 

 that this takes place as an imago and that those flies which 

 hibernate are the most recently emerged and therefore the most 

 vigorous. The abdomen of a hibernating individual is packed with 

 fat cells, the fat-body having developed enormously and the alimentary 

 canal having shrunk correspondingly. The fat- body provides susten- 

 ance during the hibernating period, and is extremely small when flies 

 which have hibernated are dissected in May and June. The natural 

 enemies and parasites of the house-fly include the pseudo-scorpion, 

 Chermes nodosus, Schr., which perhaps can hardly be regarded as a 

 true enemy, as it is possibly seeking Trombidium and other mites which 

 infest the fly. A chapter is devoted to Empusa muscae and it is pointed 



