His final enunciation of the law of parallelism in this same volume shows that he considered the development of the individual to be due to the same forces that rule evolution. "The development of the individual organism obeys the same laws as the development of the whole animal series; that is to say, the higher animal, in its gradual evolution, essentially passes through the permanent organic stages which lie below it; a circumstance which allows us to assume a close analogy between the differences which exist between the diverse stages of development, and between each of the animal classes" (p. 514). He was not, of course, able fully to prove his contention that the lower animals are the embryos of the higher, and we gather from the following passage that he could maintain it only in a somewhat modified form. "It is certain," he writes, "that if a given organ shows in the embryo of a higher animal a given form, identical with that shown throughout life by an animal belonging to a lower class, the embryo, in respect of this portion of its economy, belongs to the class in question" (p. 535). The embryo of a Vertebrate might at a certain stage of development, be called a mollusc, if for instance, it had the heart of a mollusc. He admits, too, that the highest animal of all does not pass through in his development the entire animal series. But the embryo of man always and necessarily passes through many animal stages, at least as regards its single organs and organ-systems, and this is enough in Meckel's eyes to justify the law of parallelism (p. 535). In his excellent discussion of teratology Meckel points out how the idea of parallelism throws light upon certain abnormalities which are found to be normal in other (lower) forms (p. 556).[151] We may refer to one other statement of the law of parallelism--by K. G. Carus in his _Lehrbuch der vergleichenden Anatomie_ (Leipzig, 1834). The standpoint is again that of _Naturphilosophie_. It is a general law of Nature, Carus thinks, that the higher formations include the lower; thus the animal includes the vegetable, for it possesses the "vegetative" as well as the "animal" organs. So it is, too, by a rational necessity that the development of a perfect animal repeats the series of antecedent formations. As we have said, the main credit for the enunciation of the law of parallelism belongs to the German transcendental school; but the law owes much also to Serres, who, with Meckel, worked out its implications. It might for convenience, and in order to distinguish it from the laws later enunciated by von Baer and Haeckel, be called the law of Meckel-Serres.