150 MOSQUITOES OF NORTH AMERICA 
time by overflowing sea-water from a high tide or storm, at another by the flood- 
ing from heavy rains. On the Panama coast the larve of a species of Stego- 
conops and of Aédes fluviatilis occur in rock pools of concentrated sea water 
resulting from the splash of high seas. The larve of these identical species occur 
inland in perfectly fresh water. Of most of the salt-water species it may how- 
ever be said that they adhere closely to the tide-water region; Aédes sollicitans 
may almost be said to be confined to the pools immediately back of the sea 
beaches. While these larve occur in salt or fresh water and will survive a cer- 
tain change of density of their medium, as in the case of a salt-water pool being 
diluted by rains, transfer from one medium to the other is fatal to them. The 
cause of death in this case is the osmotic action of the media of different density. 
Perhaps the most remarkable of the species breeding in salt water is Aédes 
zammittii of the Mediterranean region. According to Surgeon E. H. Ross 
they occur only in highly concentrated sea-water as it occurs in the rock-pools 
left by high tides. He states that while, in summer Mediterranean sea-water 
contains twenty-eight grammes of salt per litre, this species “can only live in 
water containing from forty-eight to eighty-seven grammes per litre of salt. 
As soon as salt begins to be formed on the surface of the pool, the larve and 
pup move on to another part of the pool, which is often most extensive. These 
pools may be very deep, but, in common with all the sea-water pools on the shore 
of the Mediterranean, never contain fish or shrimps. When a thin layer of salt 
forms on the whole surface of the pool, the larve die.” Carter found that if the 
water was sufficiently saline the larve were present, regardless whether the 
water was strongly polluted or very clean. At Port Said he found them in 
cesspools under the houses in which there was a large percentage of salt. 
THE FOOD OF MOSQUITO LARV£E. 
The larve of many species undoubtedly swallow anything in the water that 
they inhabit which can enter their mouths. With many of the species the mouth- 
brushes produce a vortex into which pass all minute objects floating on the water 
or suspended in the water. The spores of algex, particles of dust, bacteria, pro- 
tozoa, minute aquatic animals of many different kinds, are thus swallowed. With 
many species it seems that the important food is animal. Anopheles has been 
found feeding upon the dead bodies of other culicid larve. In studying the 
larvee of Anopheles quadrimaculatus in the laboratory, these insects seemed to 
thrive best in water containing green alge, and this observation has been con- 
firmed by other laboratory workers; but it has been suggested that perhaps the 
important food of these larve is after all the microscopic animal life which 
swarms among these alge and of which the alge themselves constitute perhaps 
part of the food. The alge in our experiments belonged to the genera Aédo- 
gonium, Cladophora, Spirogyra and in lesser degree Oscillaria. Stephens and 
Christophers have found that the food of Anopheles larve examined at Accra 
consisted of a unicellular organism (Protococcus?). Theobald found that the 
food sucked into the mouth of the larve of Culer pipiens and C. nigritulus 
consisted of alge and water crustacea such as Daphnia and Cyclops. He has 
