overlook, and its complete success has given a marked and decided impulse to the modern science of tunnelling through hard rock. ------ {71} 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,