In the eyes, or stemmata, this diversity is less remarkable.
This is sometimes the region of the Stemmata; or they are partly in this or partly in the Vertex.
As to the Number of the stemmata, three appears to be most universal.
Of what use then can stemmata be to insects also provided with compound eyes?
Although simple eyes (ocelli or stemmata) are common, they do not exist in all the orders of insects.
Simple eyes, or stemmata, are moreover observed in certain species, and are generally more or less hidden by scales.
The neuter of Myrmica rubra, another ant, has no ocelli or stemmata, although the male and female are provided with them.
In the Libellulina, and in the drone-bee, whose eyes are confluent, the stemmata are in the front.
From this experiment it seems as if the compound eyes were for horizontal sight, and the stemmata for vertical.
The stemmata are present only in Harpes, where there may be on the summit of the cheek two or three ocelli lying near one another.