Louis Agassiz’s Methods of Study in Natural History began as a course of public lectures at the Lowell Institute in Boston, was adapted into articles for the Atlantic Monthly, and was gathered into a book in the early 1860s. It is expository rather than narrative: sixteen chapters that move from the earliest attempts to order the animal world, through the principles of classification, to corals, embryology, and the growth of the egg. Agassiz writes for young students and curious general readers, not specialists, and he says so plainly—technicalities are avoided, the lecture-hall repetitions are kept, and only the final chapter addresses the professional naturalist directly.
The book is also, unmistakably, an argument. Agassiz uses his survey of method to strike at the transmutation theory then returning to fashion, and he does not pretend otherwise. The chapters are a complement to his earlier Essay on Classification, restating in plainer form views first set out there, and the whole performance is shaped by his conviction that the animal kingdom is the work of one Creative Intellect whose plans can be read in structure.
From Aristotle’s Unsystematic Eye to the Four Great Plans
The Memorial and the Author’s Preface
The 1869 Boston edition opens with a memorial dedication to David Jeremiah, honored as a crew member on the maiden voyage of the R/V Atlantis and as a trustee and oceanographer associated with the Woods Hole Oceanographic Institution. The title page names L. Agassiz as author; the copyright records an 1863 entry by Ticknor and Fields, and this printing is the fifth edition. In his preface Agassiz frames the collected papers as a popular complement to his earlier “Essay on Classification,” meant to give young students hints on how scientific truth has been reached. He uses the occasion, though, for a strenuous protest against the transmutation theory then enjoying wide acceptance. Naturalists, he argues, chase a phantom in seeking a material gradation by which the whole Animal Kingdom might descend from a single germ; the notion returns with hydra-headed tenacity, and he confesses a repulsive poverty in the explanation, since the Deity’s resources cannot be so meagre that a monkey must be changed into a man. He grants this is personal opinion, not argument, but insists the theory is contradicted by Embryology and Paleontology, and that experiments on domesticated animals prove nothing, since man-fostered varieties differ entirely from wild species. The chapters began as lectures at the Lowell Institute, were recorded by listeners, and were published as articles in the Atlantic Monthly; they keep the repetition proper to public lectures, and only the closing chapter addresses the professional naturalist. He signs from Nahant, August 22, 1863.
Aristotle and the Childhood of the Science
The first chapter promises a history of how men first approached Nature and converted facts into science. Agassiz likens humanity’s efforts to an individual mind’s development: early observers seem like children taking their first steps in a field so vast that all progress only shows how much remains. Aristotle stands for the learning of antiquity—a leader in intellectual culture and especially a naturalist, whose work records both his own investigations and all preceding study. Much had plainly been done even then: he refers readers to anatomical text-books for illustrations of the human frame, and Agassiz marvels that such books existed two thousand years ago while we still lack elementary natural history texts suited to our own country’s animals. One striking fact makes Aristotle’s History of Animals hard to use: it never occurred to him that Greek might cease to be the language of cultivated men, so he characterized animals by current names, and much of his account of habits is lost to us through local expression. Above all, there is no systematic framework—only genera and species, with nothing answering to our classes, orders, and families.
Nomenclature and the Comparative Method
The second chapter turns on the analogy between a student’s progress and the history of science. As civilization spread beyond Greece, a common technical language became indispensable, and Linnaeus supplied it: generic names shared by a group, with specific epithets—Felis catus, Felis leo—and Latin insisted upon to prevent confusion, whether from the same name for different animals or different names for the same. Linnaeus marked out classes, orders, genera, and species; Lamarck, bringing botanical habits to zoology, grouped animals into families, a method Cuvier adopted and perfected, making anatomy and classification march abreast. Cuvier’s secret, Agassiz says, is comparison. A dog, cat, and bear, with sharp cutting teeth, form one division; a cow, deer, and horse, with flat grinding teeth, another—yet the cow’s hollow, permanent horn separates it from the deer’s solid, yearly-shed one, and the horse’s single hoof and simple stomach from the cow’s cloven feet and four-pouched stomach. The education of a naturalist consists chiefly in learning how to compare; Agassiz sums up his own life’s work as showing a correspondence between the succession of fishes in geological times and the stages of their growth in the egg.
Cuvier’s Four Plans and Baer’s Amendment
Cuvier’s proposition that the animal kingdom rests on four plans caused extraordinary excitement. Blainville took up the element of form but erred in renaming animals already well named; Ehrenberg multiplied nervous-system categories to no purpose. Agassiz turns to Karl Ernst von Baer, who did as much for zoology as Cuvier yet is little known among us. Baer distinguished the type—Cuvier’s plan—from the complication of structure, plan from execution. His four types answer to Cuvier’s: the Peripherie or Radiates, the Massive or Mollusks, the Longitudinal or Articulates, and the Doubly Symmetrical or Vertebrates, the last named from the mode of growth, the germ dividing into two folds, one arching above the backbone to enclose the sensitive organs, the other below to enclose the organs of maintenance.
The Four Classes of Vertebrates
The argument turns first to what actually separates the vertebrate classes. Fishes are cold-blooded, breathe through gills, lay eggs, and have their own mode of circulation and reproduction. Reptiles share the cold blood but have more complicated circulation, breathe by lungs (some keeping gills for life), and lay fewer, larger eggs—fewer the higher their rank—and care for their young more than most fishes do. Birds are warm-blooded, air-breathing, double-circulation egg-layers, but with comparatively few eggs, hatched by the mother and fed by the parents until the young can fend for themselves. Mammals share warm blood and lungs yet differ from all other vertebrates in bringing forth living young and nursing them with milk. Even in the lowest of this highest group the dawning of family ties appears—the intimate bond of parent and child on which human society rests. Man crowns the work of creation, yet his physical nature is rooted in the whole type and links him even with the fish; his moral and intellectual gifts are his to use or abuse, and he may sink to the level of the lowest vertebrate or rise to a spiritual height.
The Difficulty of Orders
Chapter V takes up orders, and the author predicts that settling their true boundaries will be the greatest advance naturalists can make, since confusion abounds—some mistake orders for classes, others raise families to orders. Orders, if founded on greater or less complication of structure, must form a regular gradation within the class, and judging them demands intimate knowledge of structure throughout. An arbitrary element intrudes: one man prizes one character, another a different one, and rank shifts accordingly. The author insists this arbitrariness can be eliminated, that orders exist positively in Nature with definite limits, and that the key to the question already exists.
The Three Orders of Insects
Insects illustrate the point. They fall into three orders: the cylindrical Centipedes, ringed uniformly like worms; the Spiders, with body in two regions; and the Winged Insects, with head, chest, and hind body distinct. The nervous system follows suit—scattered throughout in Centipedes, concentrated in two swellings in Spiders, three centres in Insects, largest in the head. On this individualization of parts naturalists have ranked Centipedes lowest, Spiders next, Winged Insects highest—though some would place Spiders above Insects, or make them a class. To test the ranking against Nature, the author turns to development.
Metamorphosis as Growth
The Butterfly’s three lives—Caterpillar, Chrysalis, Winged Insect—are one life, the caterpillar as truly the same being as the child is the future man. The old poetic sense of “metamorphosis,” a fabled transformation of one individual into another, still clings and makes us overlook the continuity; to the naturalist it is simply growth, and the changes within the egg are metamorphoses too. The worm-like larva has thirteen uniform rings; the chrysalis has two regions, front rings soldered into head and chest; only the winged insect has three. An animal does not pass from more perfect to less perfect, so the history of growth is the history of progress. When each stage transiently represents a character permanent in a lower order, the gradation—Centipedes lowest, Spiders next, Winged Insects highest—is shown true to Nature. Embryology, the author concludes, will supply the standard for testing such distinctions.
Breeds Are Man’s Work, Species Are God’s
Agassiz turns to the Golden Carp as his exhibit of what domestication can and cannot do. Kept in bowls and tanks, the fish takes on spotted, striped, and variegated colors, and the Chinese, driven by what he calls a morbid love of distorted forms, have bred it into a parade of oddities: short and stout bodies, long and slender ones, swollen bellies, hunched backs, enlarged mouths, and a caudal fin—normally vertical and forked—grown crested, arched, doubled, or crooked. A book of Chinese paintings records them all. Yet not one of these variations approaches the differences that separate species within the Carp Family, which in the wild are remarkably uniform the world over. The same holds for horses, and for the whole tribe of man’s companions—dogs above all, where the gap between jackal and wolf bears no relation to the gap between bull-dog and greyhound, St. Charles spaniel and terrier, Esquimaux and Newfoundland. Donkey, goat, sheep, pig, cat, rabbit, and barnyard fowl tell the same story. Every domesticated variation traces to man’s fostering care or his fancies; wild species hold to distinct, well-defined, invariable limits. That a Chinese breeder can twist a carp into fantastic shapes no more proves that water can create a fish than that dwarfing a tree proves the earth can create a pine or an oak. Domesticated races, wherever on the globe and whatever the race of men keeping them, vary in the same manner and differ from wild species in the same manner—so they cannot explain the origin of species. They show only that an intelligent will produces effects physical causes never produce; the cause behind wild nature must therefore lie outside Nature, akin in kind to human intelligence though different in degree. Nature holds inviolable the stamp God has set upon his creatures; man’s slight influence over organization is a plasticity granted for his companionship with animals, and he is responsible for the results. Common sense has already marked the distinction with a word: these are Breeds. Breeds are the work of man; species were created by God.
The Immense Chronology of the Earth
Modern science has revealed how vast are the periods consumed in the earth’s formation—cycles before man’s appearance that make our own era seem like yesterday. Rock strata accumulated slowly; successive populations lie entombed in hardened stone; mountain chains rose in convulsions that divided ages of quiet deposition; lands sank beneath the ocean and continents rose; river-beds wore down; inland seas filled until marshes and then dry land succeeded them; coral reefs grew as sea-walls raised by tiny architects whose remains now furnish building-stone, so that whole countries, mountain ranges, islands, and coastlines consist solely of their bodies; and countless forests lived and decayed into coal. The intellect fails before such a chronology. If the succession of periods baffles estimation, can we measure even our own? The question matters for the permanence of species. Advocates of mutability dismiss historical evidence: Egyptian tombs and monuments show the animals of the Nile unchanged—the negro of the Rameses with the same woolly hair, thick lips, flat nose, dark skin; the Apis, the ibis, the crocodile, the sacred beetle all come down unaltered, no more changed than the Sphinx’s face or the Pyramids’ architecture. But the mutability camp replies, fairly enough, that six thousand years are as yesterday, and what six thousand could not do sixty thousand might. Setting historical chronology aside, how far back can our own geological period and its species be traced, and by what means shall its duration be measured—in hundreds, thousands, or millions of years?
The Lime of the Sea and the Unity of the Sciences
Where does the sea’s lime come from, the lime corals absorb in quantity? For living corals the answer is easy: rivers carry it down, and the Mississippi, draining extensive limestone regions, brings enough yearly to supply every animal in the Gulf of Mexico. The harder question is the origin of limestone at the very beginning of life on earth. That question leads to astronomy, for limestone’s base is metallic and fusible, and may have formed part of the earth’s materials in an incandescent state when worlds were forming. The inquiry belongs to neither naturalist nor geologist alone, and its very suggestion proves how intimately all the sciences are now connected; none can be carried on independently. Since the study of rocks has revealed crowded life recorded within them, geology and natural history have become one pursuit, and at the borderland where the earth’s first crust condensed from igneous materials the investigation mingles with the astronomer’s—tracing limestone in a bit of coral goes back to the creation of the solar system, when worlds were thrown off from a central mass in gaseous condition.
The Single Pattern Behind the Five Orders
Agassiz opens this stretch by marvelling at the sheer richness of early types, as though Creative Thought had lavished its wealth on the first forms brought onto the globe. After thirty years among fossil Crinoids he still meets fresh evidence of invention in the endless variation of one pattern of animal life, and long study of Nature has made it impossible for him not to see in creation the immediate action of thought—an infinite power of combination and analysis, reminiscence and prophecy. Nature, he adds, has its humorous side too. He defends the mental epithets he borrows for his descriptions: the closer one comes to Nature, the more our own intellectual endowments look like the echo of the Almighty Mind, whose eternal archetypes lie in Creation, with man as its crowning work.
No group displays this fertility more than the Crinoids, which look like the work of a hand handling its material with infinite ease and delight—the same thought under a thousand aspects. New cuts of plates, shifts in relative position, outlines running from a close cup to an open crown, from a long pear-shaped oval calyx to circular, square, or pentagonal forms; a simple angle becomes a fluted column, a smooth plate gains a symmetrical beaded figure, a stem broken only by transverse divisions puts out feathery plumes at every break, plates rigid and soldered in some forms, articulated for flexibility in others. He has amused himself anticipating new variations and rarely failed to find them among his specimens.
The modern stemless Comatula agrees with the ancient Crinoid in essential structure but drops its stem when full grown, keeping its cup-like calyx. The type is meagre now against its former richness: once the exponent of all its kind, it has dwindled as other representatives of the Class came in, and only the West Indian Pentacrinus keeps its stem in adulthood. He notes the singular fact that while a Class is represented by few types those types are wonderfully rich and varied, but as other expressions of the same structure appear, the first dwindle.
Ophiurans and the Sea-Urchin Transformed
Two Orders remain, the Ophiurans and the Holothurians. The Ophiurans come nearest the Crinoids and sit just above them: the ab-oral region so predominant in the Crinoid is now depressed—no stem, no calyx-like projection—though the ab-oral side of the disk stays quite convex in life. The disk is small beside the arms and perfectly circular, starting abruptly from its periphery instead of merging gradually into the arms as in the Star-Fish; interambulacral plates are absent, their spaces filled by the encroaching ab-oral region. Form and colour vary without limit: arms many times the disk’s diameter, short and simple in some, very long in others, stretched or contracted into graceful curves, fringed along the edges, or so ramified that each arm seems a little bush intertwining into thick net-work. In geological succession they follow the Crinoids, arriving about the Carboniferous period and perhaps earlier, with representatives in every later age and still numerous today.
To show the Holothurians’ place in the formula, he returns to the Sea-Urchins, their nearest allies. A Sea-Urchin approaches the sphere, its oral region and sides so predominant that the ab-oral region shrinks to a small area on the summit. Stretch it out from end to end into a cylinder, mouth at one extremity and ab-oral region at the other, and the zones become parallel rows running the body’s length—a Holothurian. Their form once led naturalists to class them as Worms, but their true structure, agreeing in every respect with the other Echinoderms and sharing nothing of the articulated worm plan, restored them to their proper place.
Their natural attitude causes the confusion: they lie on one side and move with the oral opening forward. Comparison, he insists, must use the “normal position,” bringing corresponding parts into the same relation in all. The Crinoid holds its ab-oral region downward on a stem, mouth upward; the Ophiuran turns its ambulacral oral region toward the surface it moves along, as does the Star-Fish; the Sea-Urchin keeps its mouth downward; the Holothurian drags itself on one side, mouth foremost. Place them all with the oral side downward and the identities leap out: the small area at the Holothurian’s far end matches the Sea-Urchin’s summit, the Star-Fish’s upper side is that region enlarged, in the Ophiuran it forms one side of the small disk, and in the Crinoid it swells into the calyx and stem.
The Difficulty of Seeing for Oneself
Agassiz opens by weighing the cost of original research. Anyone capable of it, he observes, has no time to prepare the uninitiated for the circumstances of difficult investigations or to train their eyes to see what he sees. The microscopic observer, whose insight comes from long discipline of hand, eye, and intellect, cannot pass that insight on; he may amuse visitors with easy exhibitions of specimens and open the door into Nature’s laboratory, but he cannot invite them across the threshold. People underestimate the difficulty of microscopic observation and the painful preparation needed to fit the organs of sight and touch. Nature, like a temple, does not open her sanctuary without exacting penance: some subjects are so obscure that the student must keep a special diet so that even the beating of his arteries may not disturb his gaze, and hold his whole frame rigid for hours in concentrated attention.
The Neglected Egg
Hardly any beginning has been made in studying the egg during its growth and before the germ forms. Since embryology became a science, students have aimed to show the uniform structure of the egg in all animals, confining observations to the stage when the ovarian egg appears as a perfect cell. A new field now opens, requiring careful survey of every stage of growth from the egg’s first formation to the appearance of a well-defined germ. Embryologists have generally counted their work complete once they traced the new being to a point where it somewhat resembles a member of its natural group; the process by which the whole frame is gradually completed has been assumed to be of little interest, and zoologists have overlooked the differences still distinguishing young from adult even after the typical characters are distinct. A hint might have been taken from one class of vertebrates long known for peculiar metamorphoses.
The Lesson of the Batrachians
More than a century ago Roesel, in his masterly work on the frogs and toads of Germany, represented their reproduction and growth with remarkable accuracy; Rusconi, Von Siebold, and Funke later traced the subject with greater precision. Yet no special application was made of these results to classification beyond the general recognition that the caudate batrachians with permanent external gills rank lower than the salamanders, which lose their gills in adulthood, while these in turn are inferior to frogs and toads, which resorb the tail as well. The comparison should not stop there. A more extensive examination shows the tadpole begins as an elongated body without legs and without external gills, passes to a branchiate condition with more or less developed legs before losing the gills, and exhibits various modes of limb development, phases in the formation and resorption of the tail, and stages in the formation of the fingers up to their final separation. The gradation is so complete that the changes these animals undergo furnish a complete scale, and comparing it with one founded on the structural complication of the adults, the two series agree perfectly. Nature herself supplies a classification resting on natural evidence, both embryological and zoological, with no arbitrary interference by the naturalist. What is obvious among batrachians, Agassiz has no doubt embryology will eventually accomplish for all animals, fixing their true affinities and relative standing with the utmost precision—but only once we know the growth stages of the young of every class as well as we know those of batrachians, and probably by pushing research in directions not yet dreamed of.
Metamorphoses Among Fishes
Among fishes, Agassiz reports lately discovering metamorphoses as extensive as those known among reptiles. Pisciculture is carried on at so large a scale in parts of Europe that the fact should have been found long ago; perhaps it was missed because these metamorphoses begin after hatching, when the young are apt to die in close confinement and are generally too small to be readily seen in their natural element. Yet this is the most important period of their growth for questions of affinity. He promises an early opportunity to show how young fishes, aping the gadoid or blennioid type in their transition, pass gradually into that of labroids and lophioids; how fish embryos resembling the tadpoles of frogs and toads assume the form of cyprinodonts; how apods are transformed into jugulars and abdominals, and malacopterygians into acanthopterygians; and finally, how a natural classification of fishes may be founded on the correspondence between embryonic development and structural gradation. To show how much may be expected from such investigations, he alludes briefly to facts his own studies have made him acquainted with.
What the Argument Is Really About
The spine of the book is a single claim about what a natural group is. Agassiz insists that Branches, Classes, Orders, Families, and Genera each rest on a distinct category of character, and that these categories are not conveniences of the human mind but facts written into the animals themselves. Branches rest on plan of structure; Classes on the manner in which that plan is executed; Orders on the greater or less complication of a given mode of execution; Families on form as determined by structure; Genera on the finish of special parts. Get these categories straight, he argues, and the arbitrary element that has plagued zoology—one naturalist ranking spiders above insects, another below—disappears. Classification becomes a positive science, as definite in its results as chemical analysis.
Two ideas do most of the supporting work. The first is homology, the distinction between a real structural correspondence and a mere resemblance. A bird’s wing and a man’s arm are built on the same plan; a bird’s wing and an insect’s wing are not, however alike they look and however alike they function. Agassiz treats the failure to hold this distinction as the source of most bad classification, from Cuvier’s misplaced Infusoria to the fishermen’s names—Sea-Cow, Sea-Horse, Sea-Porcupine—that record only superficial likeness. The second is the fourfold correspondence he finds running through the whole animal kingdom: rank in the adult, order of growth in the egg, succession in geological time, and distribution over the earth all tell the same story. Higher animals pass transiently through forms resembling the lower members of their own type; the first fossil-bearing rocks already contain all four great types at once. For Agassiz this convergence is the proof that the connection among animals is intellectual rather than material—that they are contemporaries in a plan, not descendants in a lineage.
Species, Breeds, and the Case Against Transmutation
The most polemical pages concern what a species is. Agassiz draws a hard line between wild species and domesticated breeds, and he draws it with real ingenuity. The Chinese, he notes, have bred the Golden Carp into a fantastic bestiary of swollen bellies, hunchbacks, and crested tails; dog fanciers have produced the bulldog and the greyhound from the same genus. But none of this variation, he argues, resembles the differences that separate wild species from one another, and none of it occurs in nature unaided. Breeds are the work of man; species were created by God. The conclusion he wants is that arguments from domestication prove nothing about the origin of species, since they demonstrate only what intelligent selection can do—and therefore point to a cause outside nature, corresponding in kind to human intelligence though different in degree.
His evidence for the fixity of species is drawn from two very different places. One is Egypt, where animals carved on the oldest monuments and preserved in tombs are identical with those living in the Nile valley now. The other is the coral reef, which he treats as a natural clock. If the immense periods required for reefs to grow can be estimated, and if the species inhabiting them have not changed across those periods, then the mutability of species is answered not by six thousand years of history but by geological time itself. The chapters on coral are not a digression from the argument; they are its long-duration test case.
The Naturalist as Reader of Structure
Running beneath the technical argument is a portrait of what Agassiz thinks a scientist is. The education of a naturalist, he says, consists chiefly in learning how to compare—his own life’s work he sums up as showing a correspondence between the succession of fishes in geological times and the stages of their growth in the egg. Cuvier’s secret was comparison; dissection and classification should march abreast, each fecundating the other. The man of science studies nature for truth’s sake and is false to his calling if he chases practical applications, which belong to the practical man. And the work is genuinely hard: the Unio shells baffled Agassiz for years before he found the test-character in the curve of the anterior end, and he warns young naturalists against the loose, name-coining work flooding the annals of science.
There is a theological frame around all of it, stated without embarrassment. The four plans of structure are parts of one great conception and the work of one Mind; the categories of classification are, as he puts it, different peculiarities of style in the same author. Man stands at the head of the vertebrates, his physical nature rooted in every characteristic of his type and linking him even with the fish, his moral and intellectual gifts his to use or abuse—he may sink as low as the lowest of his type or rise to a spiritual height. Agassiz grants that his repugnance to the transmutation theory is partly personal opinion and carries no argumentative weight; he does not accuse his opponents of irreverence. But he cannot bring himself to believe that the Deity’s resources are so meagre that, to create a reasoning human being, he must change a monkey into a man.
The Book’s Place
Methods of Study in Natural History belongs to the moment just before Darwinian evolution carried the field, and it is valuable now less as a settled account of nature than as a lucid record of the strongest case that could be made against transmutation from within the comparative anatomy of the day. Agassiz’s embryological arguments, his insistence on homology, and his fourfold correspondence were serious science, not obstruction; his reading of the fossil record and his use of coral growth as a measure of time were the work of a first-rate observer. The book also preserves a vanished idiom—the public lecture as a vehicle for original scientific argument, delivered to a Boston audience with the confidence that they could follow it. What survives best is the method rather than the metaphysics: the demand that classification rest on structure rather than resemblance, that analogy be distinguished from affinity, and that the naturalist earn his groupings by patient comparison. On those points the book still teaches, even to readers who have long since accepted the conclusion its author spent his last years resisting.
