356 THE HISTORY OF BIOLOGY 



besides these he has made considerable contributions in several other spheres of 

 anatomy: investigations into the development of the nervous system and the 

 intestinal tube in the embryonic stage, into the structure of the brain of birds, 

 into the intestinal villi, which reasons of space make it impossible to discuss 

 in detail. Finally, in his later years he collected the results of his researches 

 in a large work entitled System der vergleichenden Anatomie, which, like Rudol- 

 phi's Physiology, was never finished. The first part of it forms a summary of 

 Meckel's theoretical speculations; the following sections deal with the 

 structure of the individual organs. 



If we turn from reading Rudolphi's Physiology to Meckel's general 

 anatomy, the first impression will undoubtedly be that we have taken a 

 long step backwards in time — from a critical and almost modern method 

 of presentation back to romantic natural philosophy. The very foreword 

 contains the statement that the " Bildungsgesetze" which govern the animal 

 kingdom may be grouped under two main principles, "multiplicity" and 

 "unity," the latter also being termed "reduction." And the exposition of 

 these "formative laws" is introduced with the assertion that the form of the 

 animal may be regarded either in itself and with reference to the physical 

 force which is its origin, or with reference to the purpose intended to be 

 served thereby and the creative spiritual force that forms the basis thereof. 

 This at once is far more reminiscent of Schelling than of modern natural 

 science, and yet we constantly come across proofs of the author's many-sided 

 and radical knowledge of anatomy and of his genius for combining acquired 

 facts. By the formative law of multiplicity is meant all those qualities which 

 distinguish the life-forms from one another, and herein are included not only 

 the characters that differentiate the species, genera, and higher groups, but 

 also the qualities of the individual organs in the same and in different 

 animals and the changes in them, such as are brought about by age, habits of 

 life, and heredity. Under this heading, then, comes descriptive anatomy, while 

 the "reduction" law embraces comparative anatomy, or, as Meckel says, the 

 proofs that all formations in the animal kingdom are variations of one single 

 type — that is, the same idea that Geoffroy and Goethe tried to develop. 



Law of multiplicity 

 Under the law of multiplicity is described, to start with, the body's for- 

 mation of tissues — a chapter in which Meckel does not compare well with 

 Rudolphi in clarity and conciseness. As the fundamental substance for all 

 the parts of the body he gives a solid matter, shaped like minute globes, 

 which lie embedded in a fluid; these are clearly visible in the lower animals 

 and in the embryos of higher animals, while in the latter themselves the fluid 

 is coagulated and in conjunction with the globes forms fibres, membranes, 

 and tissues. In this speculation Meckel is without doubt influenced by Caspar 

 Friedrich Wolff, whom he held in high esteem and whose writings he trans- 



