LENGTH OF EARLY STAGES 231 
RESISTANCE TO DESICCATION. 
One of the points of importance in considering the eggs and larve of the 
malarial mosquitoes is their possible resistance of desiccation. Exact observa- 
tions on this point are still needed. Instances of supposed resistance on the part 
of larvee must be studied from every side with care before forming conclusions. 
Nuttall and Shipley give an account of two observations made at Gainsborough, 
where many fully developed larve and pup were encountered in ditches which, 
according to persons living in the vicinity, had been filled with river water after 
having been dry from four to seven days. It seemed to the authors at first that 
the larve might have been carried in with the water from the river, as larvee were 
also found there, but the larvee in the ditches were so numerous as to render this 
explanation incompetent for a large part of them. In all probability the ditches 
in question had not been completely dried out. The authors call attention to 
the fact that Christophers and Stephens in Africa found that no large larve 
Teappeared in a pool which had been dried up for two days and then refilled with 
rain-water. The larve which did appear were very small, and issued from eggs 
which apparently had resisted desiccation for the two days in question. 
James and Liston point out that when Anopheles eggs are laid on water they 
almost invariably hatch in 48 hours, but that when laid upon damp mud the 
development of the embryo goes on and when water is added the larve hatch out 
almost immediately. They point out that in Mian Mir Christophers found 
that after the water in an drrigation canal or pool had been emptied out the 
Anopheles st laid their eggs on the soft mud and that if water entered before 
the mud had become completely dry young larve would almost immediately be 
found. After giving the details of his observations, James and Liston state, “ It 
will be seen therefore, that pools which are, to all intents and purposes, quite dry, 
may contain numerous larve almost immediately after a shower of rain.” 
Christophers also found that larve may remain alive on soft mud even after 
exposure to the sun for several hors, but were killed when the mud had so far 
dried as to lose its glistening surface. 
The observers of the Instituto Oswaldo Cruz at Rio de Janeiro made experi- 
ments with Anopheles albimanus and A. argyritarsis, the two species of greatest 
economic importance in tropical America. When the larve were dried on filter 
paper, in the laboratory, they were still alive after six hours. On moist mud 
they remained alive six days. 
LENGTH OF EARLY STAGES. 
The duration of the early stages of Anopheles varies according to the tempera- 
ture and food-conditions. With the heat the growth is faster; food supply also 
governs the duration of the larval stage. In India Liston found that the larval 
state might last but a week, but with a deficient food supply it might last for a 
month. Foley and Yvernault record the development of Anopheles chaudoyet 
from egg to imago within 13 days. The early observations made by one of us 
(Howard) on Anopheles quadrimaculatus at Washington showed a minimum 
larval period, in May and June, of sixteen days, and a pupal period of five days ; 
eggs, three days—these periods undoubtedly being reduced later in the summer. 
“ 
