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I believe both thc Gyrinini and the Orecłochilini to be

while

I regard the Enhydrini as an

certain

highly evolved groups,

offshoot from an early gyrinid stock which, retaining primiti.ve characters and failing to attain the perfection of Gyri

nus or Orecłochilini, has evolved

along

lines of its own and

cannot be closely linked with either of these groups.

fuli glare of the sun,

Two divergent tendencies must have been present early in the gyrinid evolution. The one a specialization for the most arduous life of the open waters in the the other for the shaded waters of swift flowing streams. Both provide the larvae with the necessary oxygen, which shaded ponds do not, and both provide an ample food supply for thc

imago.

The Genus Gyrinus appears to be most highly evolved of all diurnal forms so perfect structurally, physiologically and psychologically are its adaptations to that modę of life and so wide its distributions. The environment is one of the most diifi-cult and dangerous of all habitats and the fact that all over the world the genus Gyrinus succeed in maintaining itself in such a habitat despite the competition of other and larger forms suggests that it is the very finished end product of this linę of evolution. The Orecłochilini which inhabit swift streams, as does Oreciochilus, are so rapid in their movement that there can be no doubt that they are highly evolved. On this point indeed OcHS and IlATCH are in agreement.

V a r i a t i o n.

others have as few as six seg-

The Family, as a whole, shows considerable variation in respect to features not of adaptive importance. The numher of segments in the antennae varies; the flagellum being nine seg-mented in some genera while ments. This reduction has apparently taken place independently in the Enhydrini and Orecłochilini. On the other hand in ada-ptive features, so spccialized is the group, great uniformity

exists.

In the materiał from Poland certain interesting peculiari-ties were to be observed. In comparison with English and South European specimens the Polish insects were on an ave-ragę slightly larger and darker with less aenescence above.