20 



after whicli the fly darts ofi suddenly. If disturbed, however, it does 

 not return to the same leaf, and an egg-mass once abandoned is never 

 completed. 



The eggs are at first white in colour, but soon change to a mottled 

 grey and then to black ; hence it is not possible to make any direct 

 observations upon embryonic development, the duration of which is 

 about five days. In hatching, the larvae leave all the eggs of a cluster 

 at about the same moment ; this occurs almost invariably in the 

 evening soon after sunset, or later. The larvae, which are very active, 

 cling together in masses, which soon lose their hold on the smooth 

 surface of the cluster and drop into the water, where the masses become 

 disintegrated and each larva moves about with a slow wriggling 

 movement. 



The young larvae are about one millimetre in length and are 

 positively phototropic, but after the first moult this is reversed and 

 they burrow into the mud, where they remain until pupation. In 

 appearance they are greyish white, elongate, tapering at both ends, 

 \vith the tracheae not yet filled with air, and the prolegs not exserted, 

 and hence presenting a more or less even surface. The very marked 

 peculiarities possessed by the very young larvae of Ckrysops enable 

 them to be differentiated from those of Tabanus. Only a few hours after 

 hatching, if in water, they begin to moult, this first moult not having 

 been noticed in Tabanid larvae. They then appear more slender and 

 slightly longer than before, with the prolegs protruding. Under 

 laboratory conditions, in water they perished in less than a week 

 without special care, and even when fed on crushed dragonfly larvae, 

 mosquito larvae and small crushed caterpillars, their numbers always 

 rapidly diminished owing to their cannibal tendencies. 



Grubbs (S. B.). Ventilation after Fumigation.^ — Public Health Repts., 

 Washington, B.C., xxxii, no. 42, 19th October 1917, pp. 1757-1761. 



The time required to ventilate the hold of a vessel after fumigation 

 ^ath hydrocyanic gas or sulphur dioxide is variable, being dependent 

 on the depth and size of the hold, area of the hatchway, velocity of the 

 wind and humidity of the atmosphere. The uncertainties and delays 

 of natural ventilation, which may take from one to twelve hours, can 

 be avoided by the use of a gasoline-driven fan worked by three 

 motors, two of the horizontal pattern (downward blast) and one of 

 the vertical pattern (horizontal blast). By this mechanical means 

 the holds of cyanide-fumigated vessels are rendered safe in 30 minutes, 

 and those that have been sulphur-fumigated in 30 to 40 minutes. The 

 installation of such a plant by steamship companies pays for itself 

 many times over in the saving of time effected. 



Phelps (E. B.) & Stevenson (A. F.). Experimental Studies with 



Muscicides and other Fly-destroying Agencies.— £/. >S. Hygienic 



Laboratory, Washington, B.C., Bull. no. 108, December 1916, 

 30 pp. 



A paper by the same authors recording these experiments and 

 results has already been abstracted [see this Review, Series B, v, p. 9]. 



