Epigenesis

Abstract

WHILE it is correct to say that, as a matter of history, epigenesis implies merely the observed fact that the fertilised egg-cell, from which the new organism of each generation arises, is, under the microscope, a nucleated mass of protoplasm not differing from other cells, it is not so certain that the simplicity of the historical conception is any help to the problem as it exists for us to-day. For in the growth of an idea as it passes from mind to mind, there is, at the best, but a formal continuity. Most often the meaning of the word has been so added to, and so taken from, that it becomes like the famous patched coat, which contained none of the original material. For the present, the question at issue is very different from the problem of those who used the word in earlier times. We know that we must not expect to see under the microscope the character of an elephant or of a mouse stamped upon the protoplasm of the fertilised egg-cell. We wish to know whether the observed facts of development and inheritance can be co-ordinated under the idea that the protoplasm of the fertilised egg-cell is as like the protoplasm of other cells as it seems; or, under the idea of preformation, that each structure of the adult has a structural representative in the egg. But many side issues arise, and identical sets of facts really devoid of bearing upon the main question are brought forward with equal triumph by advocates of either theory. Take an example, not one that, so far as this writer knows, has been employed, but which may serve as a type. The intestine of the higher animals is very much longer than the length of their bodies, and is disposed in coils and loops. Dr. Gadow has shown that this disposition in the case of birds falls into seven or eight well-marked types which are so constant as to have high corroborative value in classification. It may well be that these varieties of twisting and coiling depend upon physical conditions, upon the relations of the growing intestine to the growth and structure of the surrounding viscera and of the skeletal tissues. Here, the advocate of epigenesis would say, are characters that need no preformation in the egg, that are stamped in due course upon its simple protoplasm. But no preformationist need suppose that the invincible elements in the germ are to grow up by their own force out of all relation to surrounding conditions. The centrifugal activities of the egg, if they exist, are there to supply those differences for which there is no cause in the outer world. They supply the factor, the resultants between which and the forces of the outer world show differences under what seem to be identical conditions.

Gestaltung und Vererbung. Eine Entwickelungsmechanik der Organismen.

By Dr. Wilhelm Haacke. Pp. 337, with illustrations. (Leipzig: T. O. Weigel Nachfolger, 1893.)