132 Psyche [December 



in abundance, and the water does not have to be renewed at all. 

 The quantity of algse devoured by the larvse was quite considerable. 

 Lack of attention to this detail may perhaps explain the frequent 

 failures in rearing Anopheles larvae.^ On the other hand, the use of 

 surface algse as food may serve to determine with exactness the 

 quantity of food consumed by a single larva, since the algae, under 

 carefully chosen conditions, cover the surface quite evenly in a 

 layer of measurable thickness, and therefore the quantity of algae 

 present on a surface of given dimensions and consumed in a given 

 time may be estimated or calculated, and, divided by the number of 

 larvae feeding on this surface, would give the quantity consumed by 

 a single larva. However, as the season was advanced, and the 

 larvae were transforming into pupae, this experiment was not carried 

 out. 



The larvae 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 larvae 

 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 algae 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 algae. ^ 



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 Shipley's illustration as reproduced 



1 W. M. Graham (A study of Mosquito larvae, Jour. Ent. Research, Vol. I, 1910) has stated 

 correctly that failure to rear the larvee is not to be wondered at when it is recognized that mos- 

 quito larvae require a constant supply of special food, consisting usually of living fresh-water 

 algae. In the absence of algae the larvae become cannibalistic and destroy one another. 



2 Zetek, James. Behavior of Anopheles albimanus Wiedemann and tarsimaculatua Goeldi. 

 Ann. Ent. Soc. of America, VIII, 1915, p. 221 fif. 



' Graham, loc. cit.; these algae were not surface algae but were suspended in the water; as 

 stated, however, the Anopheles larva is mainly a surface feeder. 



