Looking through Leonard's "Flies" of 1950 and found this quote while he was discussing the female Caddis' diving to deposit her eggs:
"It has been presumed by several authorities that the wet fly was first dressed to simulate the female caddis in her underwater venture. Perhaps this is so. However, it seems more likely to me that the anglers of centuries ago observed the myriad aerial flies and copied them as best they could with the materials available, but fished them wet after the habit of using bait for so many years."
I found his musing interesting.