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tracheal gili system was as yet poorly developed, it mtist have been sluggish and slow in development. It was, however, expo-sed to far fewer dangers; once the deeper water was reached. To migrate from the shallows, teeming with enemies, into the security of the depths was difficult and dangerous. Economically it is a journey best accomplished by the adult. At first no doubt the adult, half submerged, paddled with unspecialized legs to sonie plant to lay a single batch of eggs: Carabidae may to this day be seen making their way from place to place in this manner. The danger of such a journey when it lies over

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♦ deep waters far from the shore is great. The forces of natural selection were therefore focussed upon the imago. The position is the reverse of that responsible for the evolution of the Dytiscidae. In conseąuence of this we find that whereas the larvae of the Gyrinidae are sluggish the imago is one of the most highly specialized and active of insects and has departed from the Adephagous type in many ways,

This is of course a mere hypothesis. A far morę thorough investigation of the internal anatomy of both larva and imago is reąuired before the position of the Gyrinidae can be safely established. Nevertheless it is a working hypothesis which ena-bles us to retain the Gyrinidae as a family of Adephaga and allows us to follow those who associated the Gyrinidae and Dytiscidae in the group Hydradephaga.

The arrangement of the sub-families of the Gyrinidae is also a matter of dispute. OCHS believes the Gyrinini to be the most primitive and regards the tribe Dineutini of the Sub-family Enhydrini to be the most highly evoIved, He looks upon the Orectochilini as being also highly evolved. HATCH regards the Enhydrini as primitive and the Gyrinini and Orectochilini as highly evolved. A morę detailed consideration of these authors phylogenetic speculations as they are applied to the consideration of the genera would be unprofitable but it is important that the relative positions of the sub-families should be established. My views, based on different considerations, are in close agreement with those of Hatch. I will, therefore, only discuss the arguments advanced by Ochs. His views, if I do not misunderstand him, are based on the following assumptions:

1. Smali size is primitive: as organisms evoive they become