Volume 1 — Translated from the Civiltà Cattolica. ON THE UNITY OF TYPE IN THE ANIMAL KINGDOM. I.

The generation of a human creature takes place neither by the development of a being which is found in the germ, sketched as it were like a miniature, nor by a sudden formation or an instantaneous transition from potential to actual existence. It is effected by the true production of a new being, which pre-exists only virtually in the activity of the germ communicated by the conceiver, and the successive transformation of the potential subject.

This truth, an a priori postulate of philosophy, and demonstrated by physiology a posteriori, was illustrated by us in a preceding article. Here we must discard an error which has sprung from this truth. For there have been materialists who maintained that there was but one type in the whole animal kingdom, that is, man, as he unites in himself in the highest possible degree perfection of organism and delicacy of feelings; and that all the species of inferior animals were so many stages in the development of that most perfect type. This opinion is thus expressed by Milne-Edwards in his highly esteemed lectures on the Physiology and Comparative Anatomy of Man and Animals:

"Every organized being undergoes in its development deep and various modifications. The character of the anatomical structure, no less than its vital faculties, changes as it passes from the state of embryo to that of a perfect animal in its own species. Now all the animals which are derived from the same type move during a certain time in the same embryonic road, and resemble each other in that process of organization during a certain period of time, the longer as their zoological relationship is closer; afterward they deviate from the common road and each acquires the properties belonging to it. Those that are to have a more perfect structure proceed further than those whose organization is completed at less cost. It results from this that the transitory or embryonic state of a superior animal resembles, in a more or less wonderful manner, the permanent state of another animal lower in the same zoological series. Some authors have thought right to conclude from this that the diversity of species proceeds from a series of stages of this kind taking place at different degrees of the embryonic development; and these writers, falling into the exaggerations to which imitators are especially liable, have held that every superior animal, in order to reach its definitive form, must pass through the series of the proper forms of animals which are its inferiors in the zoological hierarchy; so that man, for instance, before he is born, is at first a kind of worm, then a mollusk, then a fish, or something like it, before he can assume the characters belonging to his species. An eminent professor has recently expressed these views in a concise form, saying that the embryology of the most perfect being is a comparative transitory anatomy, and that the anatomic table of the whole animal kingdom is a fixed and permanent representation of the movable aspect of human organogeny."

Thus, according to this opinion, man is the only type of animal life; and every inferior species is but an imitation, more or less perfect, of the same; an inchoation stopped in its course at a greater or shorter distance from the term to which the work of nature tends in its organization of the human embryo. In short, an {72} entoma in difetto, to use the language of Dante.

The doctrine is not new in the scientific world. It was proclaimed in the last century by Robinet, who held that all inferior beings are but so many proofs or sketches upon which nature practises in order to learn how to form man. In the beginning of the present century Lamarck, in Germany, following Kielmayer, reproduced the same theory. According to him all the species of animals inferior to man are but so many lower steps at which the human embryo stops in its gradual development. Man, on the contrary, is the last term reached by nature after she has travelled all through the zoological scale, to fit herself for that work. About the same time the celebrated naturalist, Stephen Geoffroy Saint Hilaire, began to disseminate in France analogous ideas under the name of stages of development (arrêt de devéloppement); and these ideas, exaggerated by some of his disciples, amounted in their minds to the same doctrine of Lamarck, just alluded to. Among them Professor Serres holds the first rank, and it is to him that Milne-Edwards alludes in the passage just cited. He expresses himself thus:

"Human organogeny is a comparative transitory anatomy, as comparative anatomy is the fixed and permanent state of the organogeny of man; and, on the contrary, if we reverse the proposition, or method of investigation, and study animal life from the lowest to the highest, instead of considering it from the highest to the lowest, we shall see that the organisms of the series reproduce incessantly those of the embryos, and fix themselves in that state which for animals becomes the term of their development. The long series of changes of form presented by the same organism in comparative anatomy is but the reproduction of the numerous series of transformations to which this organism is subjected in the embryo in the course of its development. In the embryo the passage is rapid, in virtue of the power of the life which animates it; in the animal the life of the organism is exhausted, and it stops there, because it is not permitted to follow the course traced for the human embryo. Distinct stages on the one hand, progressive advance on the other, here is the secret of development, the fundamental difference which the human mind can perceive between comparative anatomy and organogeny. The animal series thus considered in its organisms is but a long chain of embryos which succeed each other gradually and at intervals, reaching at last man, who thus finds his physical development in comparative organogeny."

Thus speaks Serres. And in another place:

"The whole animal kingdom appears only like one animal in the course of formation in the different organisms. It stops here sooner, there later, and thus at the time of each interruption determines, by the state in which it then is, the distinctive and organized characters of classes, families, genera, and species."