1918] Marchand—A Thermotropism in Anopheles punctipennis 131 
eter, filled to a depth of about one and one-half inches with water . 
from a pond, more than two hundred Anopheles larvee, mostly 
collected in a half-grown stage, many of them in very young stages, 
developed into pupe. The pupze when formed were taken out 
with a pipette and transferred to another jar with provisions for 
the adults to hatch. 
In order to rear Anopheles larvee successfully, it is necessary to 
feed them, and this fact has not been sufficiently emphasized. It 
was found that certain unicellular surface alge, the species of which 
could not be determined, form a very satisfactory food. ‘These 
alge developed freely in one of the glass-covered aquaria in the 
Vivarium of Princeton University. In this aquarium they covered 
the whole surface of the water in a continuous green sheet, which 
was wrinkled and folded in places through the excessive develop- 
ment of the alge. In order to transfer these to the culture dishes 
it was sufficient to dip the finger into this stratum and then dip it 
into the Anopheles-basin; here the alge, upon reaching the clear 
surface of the water, would immediately spread out over the whole 
surface in the form of a thin, opaque, green layer. The Anopheles 
larvee would at once start feeding upon these minute alge, a clear 
area soon forming around the head and mouthparts of each larva. 
Before evening, the larve had cleared the whole surface of alge. 
The procedure was repeated at night in order to provide food for 
the larve to last until the next morning, when again the alge had 
been completely devoured. In this way they were fed regularly 
twice daily. Under ordinary conditions, when Spirogyra or other 
filamentous alge are given as food (C. A. Smith),! many larvee 
usually die, because, as a matter of fact, their natural way of feed- 
ing is at the surface. Howard, Dyar, and Knab (1912)? suggest 
that, to provide food the jars in which Anopheles larve are grown, 
should be kept uncovered, “‘in order that the dust from the air may 
settle continuously upon the water.” Undoubtedly, the Ano- 
pheles larvee may feed on surface bacteria or protozoa, but in 
absence of green plants, the contamination of the water often causes 
death. When surface algze are given, as in the case here recorded, 
practically no larvee are lost, because these algze produce oxygen 
1Cora A. Smith. The Development of Anopheles punctipennis Say. Psyche, Vol. XXI, p.1. 
2 Howard, Dyar, and Knab. The Mosquitoes of North and Central America and the West 
Indies. Vol. I, 1912. 
