A Division of Worms

Natural History, Feb, 1999 by Stephen Jay Gould

The other set of four longer comments adorns the second part of the book, on taxonomic ordering of invertebrate animals. One insertion suggests that a small and enigmatic egg-shaped fossil should be classified within the phylum of corals and jellyfishes. A second statement, of particular interest to me, revises Lamarck's description of the clam genus Trigonia. This distinctive mollusk had long been known as a prominent fossil in Mesozoic rocks, but no Tertiary fossils or living specimens had ever been found, and naturalists therefore posited an extinction for Trigonia in the great Cretaceous mass dying that also wiped out the dinosaurs. But two French naturalists then found a living species of Trigonia in Australian waters in 1802, and Lamarck himself published the first description of this triumphant rediscovery in 1803. (As an undergraduate, I did my first technical research--and also wrote my first paper in the history of science--under the direction of Norman D. Newell at the American Museum of Natural History. He gave me a half-dozen, still preciously rare, specimens of modern Australian trigonians. When I gulped and admitted that I had no experience with dissection and feared butchering such a valuable bounty, he said to me, in his laconic manner--so inspirational for self-motivated students but so terrifying for the insecure--"Go down to the Fulton Fish Market and buy a bunch of quahogs. Practice on them first." I was far more terrified than inspired, but all's well that ends well.)

The final two comments provide the greatest visceral pleasure of all, because Lamarck added drawings to his words (reproduced here with the kind permission of the book's new owner). The first sketch affirms Lamarck's continuing commitment to detail and to following and recording new discoveries. A small, white, delicate coiled shell of a cephalopod mollusk (the group including squid and octopuses) frequently washes up on beaches throughout the world. On the basis of this structure, Lamarck had proposed the genus Spirula in 1799, but the animal that makes the shell had never been found. As a particular mystery, no one knew whether the animal lived inside the shell (as in a modern chambered nautilus) or grew the shell within its body (as in the cuttlebone of a modern squid). The delicacy of the structure suggested a protected internal status, but the issue remained open. Soon after Lamarck's book appeared, naturalists discovered the animal of Spirula and affirmed an internal shell--a happy resolution that inspired Lamarck to a rare episode of artistic activity.

The last--and, as I here suggest, by far the most important--comment appears on the blank sheet following page 330, which contains descriptions of two remarkably different genera of worms--the medicinal leech Hirudo and the pond worm Planaria, known to nearly anyone who ever took a basic laboratory course in biology. Here Lamarck draws a simple sketch of the circulatory system of an annelid worm and then writes the following portentous words: