1925 ] 
Vision and Chemical Sense in Anax Larvae 
317 
Both normal insects and those with covered eyes gave no 
response to pyridine. This is interesting, because many aquatic 
insects have a strong aversion to even a minute quantity of the 
substance. Psephenus larvae, whose intense thigmotropism is 
undisturbed by the presence of formaldehyde or alkalies, will 
release their hold and make violent efforts to escape the instant 
pyridine is present in their habitat. Dytiscid larvae behave in a 
similar way. 
Although Anax larvae gave no indication of ability to sense 
the chemical nature of distant objects, it is quite evident that 
they have a sense of taste. Unpleasant substances are quickly 
rejected, and the animals move their mandibles for some time 
subsequently. 
Conclusion. 
Anax larvae distinguish small edible objects from larger 
triangular figures. Thus they distinguish the size, and probably 
the form, of objects. 
The larvae are incapable of sensing the chemical nature of a 
distant object. While antennal pits are present, they are few 
and scattered; experiment indicates that the chemical sense of 
these animals is located in the mouth. 
The perception of form and movement through vision is 
the chief means utilized by these larvae for obtaining food. 
Literature. 
Baldus, K. 1924. Experimented Untersuchungen fiber die 
Entfernungs-lokalization bei Libellen. Naturwiss. 
XXXVI. p. 725. 
Cole, L. J. 1907. Experimental Studies on the Image-forming 
Powers of Various Types of Eyes. Proc. Amer. Acad. 
Arts and Sci. XLII. p. 335. 
Demoll, A. 1910. Uber die Beziehungen zwischen Ausdehnung 
des binokularen Sehraumen und dem Nahrungserwerb bei 
einige Insecten. Zool. Jahr. (System.) XXVIII. p. 523- 
