isa-normaladvance-1909-00177

Description:	THE NORMAL ADVANCE177from the other, we have a simple case of variation.The higher and more complex organisms differ from such lowly forms only in that theyare composed of countless numbers of thesesmall units variously put together and differingfrom each other in form, size and function.Certain of these units or as they are called,cells, become highly specialized to perform certain special functions. They may be set partand developed to strengthen the body as in thewoody cells of plants or the bone cells of animals, to conduct impulses, to perform the workof secretion or absorption, in short to carryon the vital activities of the organic body.There are always certain cells which are specialized for the purpose of reproduction. Suchcells are known as germ cells. These cells areto be distinguished from the ordinary tissuecells of the body by their evident lack of differentiation and by their unlimited capacity forgrowth and development. A germ cell is simply a detached cell of the parent body whichis capable, under favorable external conditionsof passing through a cycle of development during which time it transforms itself into an individual resembling more or less closely the oneof which it once formed a part. In plants,such cells may be either sexual spores as isthe case in the non-flowering plants such asmosses, or they may be, as in animals, egg cells,which require the union with a spermatozoidconstituting the so-called process of fertilization, before they are capable of such furthergrowth and development.Darwin in his Descent of Man makes thestatement that the brain of an ant is the mostmarvelous bit of protoplasm of which we canconceive. The question quite naturally suggests itself, is the brain of the ant with all ofits wonderful ability, so marvelous or inexplicable as is the fertilized egg, which once contained potentially the ant itself? We are thusconfronted with what seems to me the mostremarkable truth in all biological science, thata single undifferentiated bit of protoplasm, thegerm cell, is able to contain within its microscopic compass the sum of the heritage of thespecies. It may develop into a whale, a fern,a daisy, a fish, frog or a man, depending onlyupon the character of the individual whichproduced it. It becomes quite clear therefore,that the germ cell is the physical basis forgenetic continuity, the mechanism of inheritance. It is at the same time heir and heritage.All that the new individual is, or is to become,because of its hereditary relationship is boundup in this small bit of living matter. The eggof a frog develops into a frog for the simplereason that it was once a part of a similarorganisni.The study of the phenomena of developmentof organisms from the germ cell, no less thanthe principle that every effect must have anadequate cause, serves only to emphasize thefact that the characteristics of an organism arein some way predetermined within the protoplasm of the fertilized egg cell. The egg of afern can develop only into a fern. The differentiations of the germ follow a definite sequencebecause the substance of the germ undergoesdefinite transformations which are predetermined by its peculiar molecular constellation.Similarity of development and hence of heredity is involved in similarity of both germinalsubstance and environment.There are no vital structures or functionswhich are absolutely independent, self-acting,self-moving, self-differentiating, or independently variable. Each part and function existsonly in close relationship with other parts andfunctions and with environmental conditions.To assume, however, that extrinsic causes aresufficient to determine the course, of development of a fertilized egg forces us to the assumption that under the same external conditions alleggs would develop the same type of organism,an assumption that resolves itself into an absurdity. To assume that external conditionsdetermine whether there shall hatch from anegg a toad or a frog is the sheerest nonsenseand yet neither of these organisms can exist
Source:	http://indstate.contentdm.oclc.org/cdm/ref/collection/isuarchive/id/34207
Collection:	Indiana State University Archives

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