106 
SPOLIA ZEYLANICA. 
confined to the island. There are only two forms of Ceylonese 
Tettix also found in the Central Province, although the range of 
the genus is of very wide dispersal from such widely separated 
places as Australia, Java, the Philippines, America,Europe, Africa. 
Systolederus has but one species here, but the genus is distributed 
in the Philippines, Celebes, Southern India, and Burma. Two 
species of Euparatettix are found in the Northern Province at 
Elephant Pass and Jaffna, as shown on the map, being also noted 
in the Central and Western Provinces. The genus extends to 
other Oriental points, such as Burma, Java, and the Philippines. 
Paratettix is known by one species in the Island. Hedotettix 
follows with three representatives from the Western and Central 
Provinces, but the genus has an extensive range outside the Island, 
having been recorded from Java, China, Philippines, Sumatra, 
and even Africa. Of two species of Copiotettix recorded from 
Ceylon there is no record of their local distribution. The genus 
extends to Java, Australia, Africa, China, and the Philippines. 
It may be well here to suggest that the cause of the restriction 
of these insects to limited areas lies in the fact of their extreme 
specialization. Those forms in which the power of flight is well 
developed and which are aided by the wind factor in their disper¬ 
sal, and are thereby carried greater or lesser distances, might 
easily survive in a new country under favourable conditions. 
They usually have a slender or prolongate body, and they live in 
the more open country. Some of the forms are evidently of great 
antiquity while others are recent. The process of appreciable 
divergence and formation of species is perceivable in some cases 
and capable of demonstration, both by measurements and in the 
appearance of subtile differences among individuals and groups 
of individuals that the experienced eye can detect. The height 
of one phase of specialization is reached in forms which resemble 
the dead twigs or leaves among which they live. The insects 
simulate these objects in shape, colour, and in the case of the leaf 
resemblance even copying to a certain degree the veins or ribs. 
This venation appears on the sides of the compressed pronotum. 
With our limited knowledge of the group the provisional inference 
reached is that the highly specialized genera like the apterous 
Deltonotus living on the bed of the forest among the dead leaves 
in the mountainous region has been isolated from a remote period. 
Acknowledgments . 
The present study is the outcome of the very generous action 
of Mr, E* Ernest Green, Entomologist on His Majesty’s service in 
Ceylon, in placing in my hands a collection of specimens which 
