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expected to give rise to the large somewhat elongated Dineu-/us-like forms known to have existed in the Miocene. Such a view is in accord with the course of evolution found in se-veral successful groups of Arthropods and Vertebrates in which there is at first a tendency for size to increase followed by a diminution of size and a perfecting of structure, physiology and psychology. Unfortunately for such hypothesis Gyrinoides ałauus Heer from the lower Lias is 3-5 mm in length and Gyrinoides

O

limbatus Mots. from the Baltic Amber has a length of 2.25 mm only. The question of size is however unimportant. Large forms of the dimensions of a Cybister or Hydrous or smali species of the size of a smali Bidessus or Limnebius could not take advan-tage of the surface tension. The actual size variation known to exist within the group is conseąuently smali. Ali that can safely be said is that, owing to the naturę of the environment, smali species must be perfect in their adaptations and, conseąuently, we may expect to find amongst them those most highly evolved.

That the Gyrinidae should be considered as a family of the Adephaga is reasonable. Many of the best entomologists have, however, doubted it. O CHS considers that they have arisen from a pre-carabid stock, have affinities with the Palpi-cornia and are to be ranked as a „super-family” Gyrinoidea. The modern tendency to separate morę and morę widely every animal group, from the standpoint of the systematist, is to be deplored. In this case it appears unnecessary. The characters which separate the Gyrinidae from other Adephaga are adaptive, and conseąuently have little or no classificatory importance. HATCH has been so impressed by this that he derives the Gyrinidae from the Dytiscidae through the Palaeogyrinidae. Both OCHS and HATCH believe that transition from an aąuatic to a surface swimming life is simple: it is not. This has lead HATCH to propound an hypothesis which is too facile to be true and has induced Ochs to separate widely the Gyrinidae from the Dytiscidae. They have concentrated their attentions upon the imago: it is the similarity of the larvae of the two families which is significant.

The common ancestor of both the Dytiscidae and Gyrinidae was no doubt, a terrestrial beetle with an aąuatic larva, The aąuatic habits of the adult insects were a much later