The Organization And Cell Lineage Of The Ascidian Egg

Author : Edwin G. Conklin
Publisher :
ISBN 13 : 9781332305292
Total Pages : 174 pages
Book Rating : 4.3/5 (52 download)

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Download or read book The Organization and Cell-Lineage of the Ascidian Egg (Classic Reprint) written by Edwin G. Conklin and published by . This book was released on 2015-08-05 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Excerpt from The Organization and Cell-Lineage of the Ascidian Egg May not these differentiations appear at still earlier stages and "organ-forming germ regions" be marked out in the egg before cleavage begins. Finally does the organization of the egg arise de novo in the ovary, or may a certain part of it be carried over from generation to generation, and is this early organization of the egg in any way different from the organization of any cell? These are problems of profound importance which lie at the basis of any thorough study of development, inheritance and evolution. B. Ascidian Embryology. - Anyone who has observed the ascidian egg will understand why it has been such a favorite object of study. The cleavage of the egg is so beautifully regular and can be observed so readily in life that it is not surprising that ascidians were among the first animals to which the "cell-lineage" method was applied. It is surprising, however, to find such diversity of opinion with regard to the development of these animals; even in some of the most important points in the early development, such as the relation of the poles of the egg to those of the gastrula, or the cell origin of the germ layers, scarcely two authors agree, in spite of the fact that these eggs are perhaps as favorable as any others in the whole animal kingdom for the stud of these problems. Under the circumstances it is impossible to avoid the conclusion that a large amount of very careless work has been done in this field. Accuracy is ever the avowed aim of science, and when one finds scientific work unpardonably inaccurate he may justly feel indignant. For some reason or other ascidian embryology has ever been a field of conflict and confusion. In some cases controversy has raged for years around a mere blunder which has thus gained a sort of immortality rarely attained by accurate work. But ascidian embryology furnishes illustrations not only of inaccurate work; it also affords some of the most classical examples of accurate and substantial research. Considering the time when the- were written, Kowalevsky's papers (1866, 1871) are models of accuracy. The beautiful studies of Van Beneden and Julin on the segmentation of the ascidian egg and on the morphology of the tunicates (1884, 1886) surpass in excellence anything which had been done up to that time, and in some respects they have not been equalled by an more recent work on the development of these animals. Chabry's (1887) classical paper on the normal and teratological embryology of ascidians is a masterpiece, - one of the first and best illustrations of the application of the experimental method to the study of embryology. After this, the most important work dealing with the early development of ascidians is that of Castle (1894, 1896), although it is marred by some fundamental mistakes; he has applied in detail the method of cell lineage to the study of the development of Ciona intestinalis, and has followed the history of the individual cleavage cells farther than had any of his predecessors. Other work which deserves mention has been done by Kupffer (1870), Seeliger (1885), Davidoff (1889), Samassa (1894) and others, and will be referred to later in the body of this work. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com