THESE 31 ESSAYS were taken from Stephen Jay Gould's monthly columns in Natural History magazine. He has added a few postscripts, and he states in a prologue that he hopes to avoid "that incubus of essay collections, diffuse incoherence" by focusing upon evolutionary theory, with special emphasis on Darwin.

Another incubus he dreads is the essay consisting of singular tales told for their own sake: the ways of the arachnid, the giraffe and so forth. Instead, each anecdote should be related to a principle: "pandas and sea turtles to imperfection as the proof of evolution, magnetic bacteria to principles of scaling, mites that eat their mother from inside to Fisher's theory of sex ratio."

Gould happily admits his own delight in odd facts, "But each organism can mean so much more to us. Each instructs; its form and behavior embodies general messages if only we can learn to read them. The language of this instruction is evolutionary theory."

So he ambles through the wilderness like an erudite scoutmaster pointing out, elucidating, and coordinating various marvels for his troop. Speaking as one scout, I could do with less scientific argument, but of course the next tenderfoot might ask for more. How much you get out of the following passage, for instance, probably depends on your bias: "Thus we may pass from the underlying genetic continuity of change -- an essential Darwinian postulate -- to a potentially episodic alteration in its manifest result -- a sequence of complex adult organisms. Within complex systems, smoothness of input can translate into episodic change in output."

Quite a lot of such enlightening verbiage occurs in The Panda's Thumb because Gould has chosen to address readers with some background in natural history and a decided taste for evolutionary mechanics. Still, those who respond more to particularities than to hypotheses will meet a gaggle of Byzantine characters.

The life and times of that matricidal mite, for example, is hideous and perfectly astounding. We are told that each female mite attaches herself to the egg of a thrip, which serves as nourishment during her egg-producing period. The larvae -- one male and approximately half-a-dozen females -- do not hatch outside her body but inside, and spend the next two days literally eating her alive. At the end of this time they are mature. The male copulates with his sisters, after which they all chew holes in their mother's carcass and emerge. The females, naturally go looking for thrip eggs. The male reacts "however a mite does to the glories of the outside world," and then -- being of no further use -- expires. Gould does not imply a parallel to the life and times of Homo sapiens, so you must evaluate that possibility yourself.

Then we have the catastrophic flood which swept the Columbia Plateau when a glacier withdrew -- thereby quickly draining an enormous lake in western Montana. Engineers calculate that 752,000 cubic feet of water per second roared down the scabland flow channels. That amount may not impress anybody except a hydraulic engineer, until you learn that such a flood could transport 36-foot boulders.

Gould's catalogue is diverse. He recapitulates the famous Piltdown Hoax, providing a new suspect; he contemplates the callosities on the legs of ostriches; he explains why the spirals in a pine follow the Fibonacci series; he delivers a fascinating lecture on the neoteny of Mickey Mouse, who has grown younger and more innocuous these past 50 years.

He excerpts from an 1879 article published in a French anthropological journal: "In the most intelligent races, as among the Parisians, there are a large number of women whose brains are closer in size to those of gorillas than to the most developed male brains. This inferiority is so obvious . . ." etc. One is tempted to quote further, but these days it would be suicidal, so if you care to know what else that French scientist thought, you will have to look it up in Gould's book.

He comments on the persistent appeal of Lamarck: "It reinforces two of our deepest prejudices -- our belief that effort should be rewarded and our hope for an inherently purposeful and progressive world."

He mentions that Einstein's brain -- what's left of it -- now rests "in a Mason jar packed in a cardboard box marked 'Costa Cider' . . . in Wichita, Kansas." How it got there, he does not say. It sounds like the end of a Chekhov story. At any rate, if the realization that Einstein's brain is in Wichita makes you ask what the world is coming to, my friend, you are not alone.

And once in a while he says something you are not apt to forget, such as the fact that nearly all important ideas arise more than once, often simultaneously.

So The Panda's Thumb does not consist altogether of the dense foliage of scientific thought; Gould has embellished his evolutionary tree with a good many appealing ornaments and winking lightbulbs.