A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...

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162 GILBERT 0. BOURNE. sitions as we may make are but resting-places for our minds as we ascend the mazy scale of organisation. To attempt to form definitions, to predicate the precise attributes of whole classes of phenomena, is to run counter to the very genius of the subject. For what do we mean by evolution if not that life is labile, never resting, protean in its variety? And how can we express this but in an incomplete way, contenting ourselves with particulars, and trying to show that the stream, though it flows in many tortuous channels, is one stream nevertheless. Cells and nuclei are protean in their variety, and since we very rightly insist on objective study as a preliminary to the understanding of them, it is not wonderful that they should give rise to this concept in the mind of one man, and to that concept in the mind of another man, and thus it is not surprising that the theory of cells should be incapable of being stated, as Mr. Sedgwick complains, "in so many words in a manner satisfactory to everyone." It is fairly obvious that Mr. Sedgwick's quarrel with the cell-theory began with the dissatisfaction which he felt when he discovered that doctrines, which he believed to be of universal application, were in fact contradicted by several instances. But he fell out of Scylla into Charybdis when he supposed that he could reply to a uuiversal affirmative by a universal negative. There is an old and respectable rule of logic that of two contrary propositions both cannot be true and both may be false, whilst of two subcontrary propositions both may be true but both cannot be false. Had Mr. Sedgwick remembered this, he would not have attempted to overthrow the cell-theory by the statement of a contrary proposition of equally universal import. The cellular theory of development in the popular form in which it is often presented may be briefly summed up somewhat as follows. The multicellular organism is a colony, consisting of an aggregation of separate elementary parts, viz. cells. The cells are independent life units, and the organism
A CRITICISM OF THE CELL-THEORY. 163 subsists in its parts and in the harmonious interaction of those parts. The falsity of this summary is evident when we consider the known facts of vegetable organisation; the development of Peripatus; the union, by means of protoplasmic processes, of epithelial, muscular, and connective-tissue cells; the evidence lately adduced as to the continuity of the mesoblast in Elasmobranchs, Aves and Mammalia, and other well-known instances. The absolute contrary, as expressed by Mr. Sedgwick, is equally false, viz. that the metazoon is a continuous mass of nucleated vascular protoplasm, subsisting in the unity of its mass. For, as I have shown in the earlier part of this essay, there are unequivocal instances of distinct isolated cells occurring in the embryos of many Metazoa (Nereis, Unio, Umbrella, Leptoplana). Moreover I am convinced, by my own studies on the histology of Coelenterates, that, whilst there is organic connection between many of the tissue-cells composing these organisms, as was demonstrated long ago by the brothers Hertwig, there are many other cells of which such continuity cannot be affirmed. To deal clearly with the cell-theory, or rather with the independent-life-unit theory which has grown out of it, we must split it up into as many separate propositions as it contains. These are: The multicellular organism is an aggregate of elementary parts, viz. cells. The elementary parts are independent life units. The harmonious interaction of the independent life units constitutes the organism. Therefore the multicellular organism is a colony (cellrepublic according to Hiickel). It is not necessary to follow the theory further into the consequences which are deducible from these propositions, e. g. that development consists in the separation of numerous individual units from a single primary unit, the ovum. It is obvious that the truth of the first proposition in no way depends on the truth of those which follow, and that, in fact,
Page 1 and 2: A OEITIOISM OF THE GULL-THEORY. 137
Page 3 and 4: A CRITICISM OP THE DELL-THEORY. 139
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Page 7 and 8: A CRITICISM OF THE CELL-THEORY. 143
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