The bell is the least important part of the clarinet. After all, only low E and middle B use the bell's length.

Wooden bells often crack with the grain because of the shape, and because the bell often absorbs the shock if the instrument is dropped. If a wooden bell cracks, it won't effect the tone unless it rattles with sympathetic vibrations. (I have never seen this happen.) If your wooden bell cracks enough to cause concern, just cover the crack with tape or fill it with epoxy.

The left bell is from my Forte Bflat Clarinet. Notice that it comes from the factory with a hole in it. I like this feature because I almost always sit when I play. If the clarinetist sits down and plays with the bell resting on or between his/her legs, the middle B and low E can be muffled and flattened. The hole eliminates the problem. It seems to me that all normally shaped clarinet bells should have a hole like this. Without it, the player must remember to raise the instrument for those notes. [May2013 update: I would now say that hole in the left bell is too big and too high up. But I still like having a hole.]

If your bell breaks, it is very easy to replace. Just grab a bell from an old junk clarinet. It doesn't need to be the same brand. It won't make any difference.

Sherman Friedland has some interesting comments on bells here.

The clarinet bell doesn't need so much flare. The Mazzeo system clarinet (right) was made with much less flare to the bell.

AND, you've seen it here first, folks! The Backpackable Bell !

Not exactly delicate,
this is two PVC pipe fittings put together.
The smaller is a 1 inch coupling,
and the other is a 1 1/2 to 1 inch bushing.

The smaller piece is not pushed in all the way into the larger piece.
Almost 3 1/2 inches long seems to play in tune for me.

Using this barrel really only affects the tone of the middle B and the low E,
and there is hardly any difference in tone! 

It just feels different to the player because of being so much lighter in weight.

The Backpackable Bell will fit nicely into the back-packable tackle boxes I recommend as an idea for students.

This page has information about this ca. 1880 carved bell:

This picture is from, the new Australian maker: