When a man has a sensitive or sore spot in his heart, from the pain of which he would gladly flee to the ends of the earth, it is marvellous what coincidences of events will be found to press upon it wherever he may go. Singularly enough, one of the first items in the confession of the Capuchin Superior related to Agnes, and his story was in substance as follows. In his youth he had been induced by the persuasions of the young son of a great and powerful family to unite him in the holy sacrament of marriage with a protégée of his mother’s; but the marriage being detected, it was disavowed by the young nobleman, and the girl and her mother chased out ignominiously, so that she died in great misery. For his complicity in this sin the conscience of the monk had often troubled him, and he had kept track of the child she left, thinking perhaps some day to make reparation by declaring the true marriage of her mother, which now he certified upon the holy cross, and charged Father Francesco to make known to one of that kin whom he named. He further informed him, that this family, having fallen under the displeasure of the Pope and his son, Cæsar Borgia, had been banished from the city, and their property confiscated, so that there was none of them to be found thereabouts except an aged widowed sister, who, having married into a family in favor with the Pope, was allowed to retain her possessions, and now resided in a villa near Rome, where she lived retired, devoting her whole life to works of piety. The old man therefore conjured Father Francesco to lose no time in making this religious lady understand the existence of so near a kinswoman, and take her under her protection.—Thus strangely did Father Francesco find himself again obliged to take up that enchanted thread which had led him into labyrinths so fatal to his peace.
[METHODS OF STUDY IN NATURAL HISTORY.]
V.
It is in the search after the true boundaries and characteristics of orders that we may expect the greatest advance by the naturalists of the present day; and yet there is now much discrepancy among them, some mistaking orders for classes, others raising families to the dignity of orders. This want of agreement in their results is not strange, however; for the recognition of orders is indeed exceedingly difficult. If they are, as I have defined them, groups in Nature founded upon a greater or less complication of structure, they must of course form a regular gradation within the limits of their class, since comparative perfection implies comparative rank, and a correct estimate of these degrees of complication requires an intimate and extensive knowledge of structure throughout the class. There would seem to be an arbitrary element here,—that of our individual appreciation of structural character. If one man holds a certain kind of structural characters superior to another, he will establish the rank of the order upon that feature, while some other naturalist, appreciating a different point of the structure more highly, will make that the test character of the group. Let us see whether we can eliminate this arbitrary element in our estimate of these groups, and find any mode of determining orders that shall be unquestionable, and give us results as positive as a chemical analysis according to quantitative elements. I believe that there are such absolute tests of structural relations. It is my conviction, that orders, like all the other groups of the Animal Kingdom, have a positive existence in Nature with definite limits, that no arbitrary element should enter into any part of our classifications, and that we have already the key by which to solve this question about orders.
To illustrate this statement, I must return to the class of Insects. We have seen that they are divided into three orders: the long cylindrical Centipedes, with the body divided throughout in uniform rings, like the Worms; the Spiders, with the body divided into two regions; and the Winged Insects, with head, chest, and hind body distinct from each other, forming three separate regions. In the first group, the Centipedes, the nervous system is scattered through the whole body, as in the Worms; in the Spiders it is concentrated in two nervous swellings, as in the Crustacea, the front one being the largest; and in the Insects there are three nervous centres, the largest in the head, a smaller one in the chest, and the smallest in the hind body. Now according to this greater or less individualization of parts, with the corresponding localization of the nervous centres, naturalists have established the relative rank of these three groups, placing Centipedes lowest, Spiders next, and Winged Insects highest. But naturalists may, and indeed they actually do, differ as to this estimation of the anatomical structure. Have we, then, any means of testing its truth to Nature? Let us look at the development of these animals, taking the highest order as an illustration, that we may have the whole succession of changes. All know the story of the Butterfly with its three lives, as Caterpillar, Chrysalis, and Winged Insect. I speak of its three lives, but we must not forget that they make after all but one life, and that the Caterpillar is as truly the same being with the future Butterfly as the child is the same being with the future man. The old significance of the word metamorphosis—the fabled transformation of one individual into another, in which so much of the imagination and poetical culture of the ancients found expression—still clings to us; and where the different phases of the same life assume such different external forms, we are apt to overlook the fact that it is one single continuous life. To a naturalist, metamorphosis is simply growth; and in that sense the different stages of development in animals that undergo their successive changes within the egg are as much metamorphoses as the successive phases of life in those animals that complete their development after they are hatched.
But to return to our Butterfly. In its most imperfect, earliest condition, it is Worm-like, the body consisting of thirteen uniform rings; but when it has completed this stage of its existence, it passes into the Chrysalis state, during which the body has two regions, the front rings being soldered together to form the head and chest, while the hind joints remain distinct; and it is only when it bursts from its Chrysalis envelope, as a complete Winged Insect, that it has three distinct regions of the body. Do not the different periods of growth in this highest order explain the relation of all the orders to each other? The earliest condition of an animal cannot be its highest condition,—it does not pass from a more perfect to a less perfect state of existence. The history of its growth is, on the contrary, the history of its progress in development; and therefore, when we find that the first stage of growth in the Winged Insect transiently represents a structural character that is permanent in the lowest order of its class, that its second stage of growth transiently represents a structural character that is permanent in the second order of its class, and that only in the last stage of its existence does the Winged Insect attain its complete and perfect condition, we may fairly infer that this division of the class of Insects into a gradation of orders placing Centipedes lowest, Spiders next, and Winged Insects highest, is true to Nature.
This is not the only instance in which the embryological evidence confirms perfectly the anatomical evidence on which orders have been distinguished, and I believe that Embryology will give us the true standard by which to test the accuracy of our ordinal groups. In the class of Crustacea, for instance, the Crabs have been placed above the Lobsters by some naturalists, in consequence of certain anatomical features; but there may easily be a difference of individual opinion as to the relative value of these features. When we find, however, that the Crab, while undergoing its changes in the egg, passes through a stage in which it resembles the Lobster much more than it does its own adult condition, we cannot doubt that its earlier state is its lower one, and that the organization of the Lobster is not as high in the class of Crustacea as that of the Crab. While using illustrations of this kind, however, I must guard against misinterpretation. These embryological changes are never the passing of one kind of animal into another kind of animal: the Crab is none the less a Crab during that period of its development in which it resembles a Lobster; it simply passes, in the natural course of its growth, through a phase of existence which is permanent in the Lobster, but transient in the Crab. Such facts should stimulate all our young students to embryological investigation as a most important branch of study in the present state of our science.
But while there is this structural gradation among orders, establishing a relative rank between them, are classes and branches also linked together as a connected chain? That such a chain exists throughout the Animal Kingdom has long been a favorite idea, not only among naturalists, but also in the popular mind. Lamarck was one of the greatest teachers of this doctrine. He held not only that branches and classes were connected in a direct gradation, but that within each class there was a regular series of orders, families, genera, and species, forming a continuous chain from the lowest animals to the highest, and that the whole had been a gradual development of higher out of lower forms. I have already alluded to his division of the Animal Kingdom into the Apathetic, Sensitive, and Intelligent animals. The Apathetic were those devoid of all sensitiveness except when aroused by the influence of some external agent. Under this head he placed five classes, including the Infusoria, Polyps, Star-Fishes, Sea-Urchins, Tunicata, and Worms,—thus bringing together indiscriminately Radiates, Mollusks, and Articulates. Under the head of Sensitive he had also a heterogeneous assemblage, including Winged Insects, Spiders, Crustacea, Annelids, and Barnacles, all of which are Articulates, and with these he placed in two classes the Mollusks, Conchifera, Gasteropoda, and Cephalopoda. Under the head of Intelligent he brought together a natural division, for he here united all the Vertebrates. He succeeded in this way in making out a series which seemed plausible enough, but when we examine it, we find at once that it is perfectly arbitrary; for he has brought together animals built on entirely different structural plans, when he could find characters among them that seemed to justify his favorite idea of a gradation of qualities. Blainville attempted to establish the same idea in another way. He founded his series on gradations of form, placing together, in one division, all animals that he considered vague and indefinite in form, and in another all those that he considered symmetrical. Under a third head he brought together the Radiates; but his symmetrical division united Articulates, Mollusks, and Vertebrates in the most indiscriminate manner. He sustained his theory by assuming intermediate groups,—as, for instance, the Barnacles between the Mollusks and Articulates, whereas they are as truly Articulates as Insects or Crabs. Thus, by misplacing certain animals, he arrived at a series which, like that of Lamarck, made a strong impression on the scientific world, till a more careful investigation of facts exposed its fallacy.