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larger.—This is by no means always true. Even if it were true the size variation in the Gyrinidae would not be sufficient to serve as a criterion.

2.    The primitive Gyrinidae pupated on emergent yegetation. — This argument is void. Gyrinus makes a pupal chamber of earth like other genera.

3.    The open water life on still waters is primitive.—This view needs careful consideration. The primitive larva almost certainly required still or slow flowing water and a rich oxy-

t

gen supply. It, no doubt, inhabited banks of submerged weed in open water, The imago likewise required still water as it could not have paddled across swift flowing water. To this extent OCHS argument holds. The adult, however, is not likely to have been able long to endure the rays of the sun, It was, no doubt, like many insects with aquatic larvae, a nocturnal or semi-nocturnal creature, haunting the shades by day and jour-neying over the waters in the evening or at night. The difficul-ties of life on sunlit waters are many. To overcome them requ-ires a highly perfected constitition, OCHS argument is conse-quently invalid,

4.    That a large number of elytral striae is morę primitive than a smali number.—This seems to me purcly hypothetical, The carly fossil forms appear to have had smooth elytra. If this is any indication, the converse of his supposition is the correct view.

5. Ihat a wide geographical distribution indicates an an-cient type.— Amongst sedentary organisiris of recent evolution this is, no doubt, partly true: WlLLIS¹) has brought forward a large amount of data to show that it is so. Many exceptions are, however, to be found, even amongst organisms which have limited means of dispersal. It is not applicable to animals which can fly and are migratory in their habits, Amongst such crea-tures a wide distribution is an indication not of antiquity but of yirility. The Genus Gyrinus was well established in the early

Pleistocene.

They are good fliers and are migratory in

habit.

The fact that they have a world wide distribution is not surpri-sing: individual species of Dytiscidae are almost as wide-spread.

1

W i 1 1 i s, 1922, A*se and Area. Cambridge.