132 Psyche [December 
in abundance, and the water does not have to be renewed at all. 
The quantity of algee devoured by the larvee was quite considerable. 
Lack of attention to this detail may perhaps explain the frequent 
failures in rearing Anopheles larvee.! On the other hand, the use of 
surface alge as food may serve to determine with exactness the 
quantity of food consumed by a single larva, since the alge, under 
carefully chosen conditions, cover the surface quite evenly in a 
layer of measurable thickness, and therefore the quantity of alge 
present on a surface of given dimensions and consumed in a given 
time may be estimated or calculated, and, divided by the number of 
larve feeding on this surface, would give the quantity consumed by 
a single larva. However, as the season was advanced, and the 
‘larve were transforming into pupe, this experiment was not carried 
out. 
The larve showed in a remarkable degree the characteristic in- 
stinct spoken of by Zetek,” to drop to the bottom when a shadow 
passed over their heads. When the writer came near them, in 
the morning, after they had been completely undisturbed for many 
hours, the phenomenon was particularly striking. The larve 
would drop almost simultaneously and then would remain at the 
bottom for several minutes. 
In this connection, it may be noted that Graham has stated that, 
in the Sudan, microscopic fresh-water alge form the principal food 
of Anopheles, a fact not unimportant for their control, since it 
may be that the mosquitoes may be kept in check by methods 
aiming at a destruction of the alge.® 
II. Bionomics of the Adult Stage. 
The resting position of Anopheles has often been used as a char- 
acteristic to distinguish the malarial mosquito from other species, 
the Anopheles holding the body, as a rule, at a certain angle to the 
surface on which they are resting. This angle is, in A. punctipennis, 
usually about 45°; Nuttall and hipley’s illustration as reproduced 
1 W. M. Graham (A study of Mosquito larve, Jour. Ent. Research, Vol. I, 1910) has stated 
correctly that failure to rear the larve is not to be wondered at when it is recognized that mos- 
quito larve require a constant supply of special food, consisting usually of living fresh-water 
alge. In the absence of alge the larve become cannibalistic and destroy one another. 
2 Zetek, James. Behavior of Anopheles albimanus Wiedemann and tarsimaculatus Goeldi. 
Ann. Ent. Soc. of America, VIII, 1915, p. 221 ff. 
3 Graham, loc. cit.; these alge were not surface alge but were suspended in the water; as 
stated, however, the Anopheles larva is mainly a surface feeder. 
