The epic credit crisis and its effects are bringing an ignominious end to the Wall Street we've known for many decades. What will replace it? Considering the reactions to other financial crises during our lifetimes -- all of which have been far less severe than the current one -- the future seems to hold two things: a long period of intense risk aversion and the most sweeping regulatory overhaul since the Great Depression.

In each of these developments there is both cause for great concern and the prospect of great opportunity. Exchange volumes, following today's panic-fueled spasm of volatility, should soften as retail investors exit the markets and hedge funds fold and continue to de-lever. However, the emergence of high-frequency market makers as the driving force behind today's markets should provide a floor for overall trading activity, as these firms are not buffeted by fund outflows and should continue to trade even in an extended downturn. Still, liquidity is likely to be less available for everyone, and that will make trading skill and knowledge of market structure more important during the next decade than ever before.

Capital will remain scarce for a long while. The continuing trend away from intermediaries committing capital and toward agency brokerage will accelerate as big banks hoard capital and institutions demand first-rate execution. In down and turbulent markets, trading efficiency can save precious basis points that affect performance -- and thus client asset flows -- far more profoundly than they do in bull markets. On the Wall Street of tomorrow, investors will no longer be able to justify executing trades with lousy brokers in exchange for good research or other nonexecution services. Unbundling of the various items that have traditionally been paid for with brokerage commissions should intensify.

Risk aversion and demand for greater transparency will also have extensive effects on market structure. Regulated exchanges have performed admirably during the crisis, even as concerns have mounted about the risks of over-the-counter markets. One of the biggest opportunities of the new era will be the chance that exchanges have to claim OTC business. This will be most pronounced in the approximately $54 trillion market for credit default swaps. Following the collapses of big CDS players such as Bear Stearns and Lehman Brothers, regulators have grown gravely concerned about the lack of central clearing and transparency in the CDS market, fearing that the situation permits the accumulation of excessive counterparty risk. Several exchanges, including Deutsche Boerse, CME Group, ICE and NYSE Euronext, have responded to regulators' call for a solution, with the likely outcome being a new central counterparty for CDSs and perhaps the migration of some OTC contracts to exchanges.

Regulation, of course, is fraught with risk of its own. New rules often trigger unintended, negative consequences. Lawmakers will likely respond to this massive crisis with an equally gargantuan re-regulation of the financial services industry aimed at reducing risk and boosting transparency. U.S. regulators will need to bear in mind that finance today is far more global than it was in 1933, when our current regulatory regime was designed. Mistakes made today won't just mean painful unintended consequences and heading back to the drawing board a few years hence. They could drive U.S. financial activity overseas, on a large scale. Here's to hoping the next Wall Street isn't the last.