Eugenio Rignano upon the Inheritance of Acquired Characters

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: of the lens. For the cells of the iris cannot preserve within them potentially any trace of a formative capacity, or of a germinal anlage, or of any determinant which provokes the formation of the lens, seeing that in normal development the latter takes its origin from another tissue. In these examples,...
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Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: of the lens. For the cells of the iris cannot preserve within them potentially any trace of a formative capacity, or of a germinal anlage, or of any determinant which provokes the formation of the lens, seeing that in normal development the latter takes its origin from another tissue. In these examples, both in the post generation of Roux's half embryos and in the regeneration of the lens in the triton, the cells which serve as constructive material appear then to be absolutely incapable of any auto-transformation and ready on the contrary to differentiate themselves and to dispose themselves indifferently in any manner whatever, according to the formative stimulus to which they happen to be exposed. At this point the fundamental biological question presents itself: What is the nature of these formative stimuli, of this continued action which the formative part exercises upon the part being formed? The attempt to build up a hypothesis relating to so important a question is the object of the studies presented in the second part of this chapter. 2. Hypothesis of the Nature of the Formative Stimulus If, in our study of the nature of the formative stimulus in the development of organisms, we start with the primitive pluricellular form, consisting simply of aggregations of cells that are all alike, we observe that during some stages of their ontogeny the essential nature and the behaviour of these cells is clearly determined by phenomena of nervous nature in the widest sense of the word. For example, phenomena of this nature exist undoubtedly in the little mononuclear amoebae into which the spores of the myxomycetes become changed, also inthe zoospores which move about by means of their vibratile flagella and into which these mononuclear amoebae become transformed. A...