File:Morgan 1925 fig34.jpg

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Fig, 34. Diagram illustrating the two maturation divisions of the germ cells in the male

In a the chromosomes appear as thin threads (leptotene stage). These conjugate in pairs, b, beginning at the two ends of each loop.

The threads contract, and a spindle appears, d, near the nucleus. The conjugating chromosomes enter the spindle, d. There they separate, e, moving to opposite poles of the spindle. The cell protoplasm begins to constrict, f.

The chromosomes may without entering upon a resting nuclear stage pass onto a new spindle that has developed by the division of each of the centrosomes of each daughter cell, g. Each chromosome now splits throughout its length (equational division) ; half of each goes to one or the other pole. The two daughter cells then divide, giving four cells, each of which differentiates into a spermatozoon.

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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Morgan (1925) Evolution and Genetics: 1 Different Kinds of Evolution | 2 Four Great Historical Speculations | 3 Evidence for Organic Evolution | 4 Materials of Evolution | 5 Mendel's Two Laws of Heredity | 6 Chromosomes and Mendel’s Two Laws | 7 Linkage Groups and the Chromosomes | 8 Sex-Linked Inheritance | 9 Crossing-over | 10 Natural Selection and Evolution | 11 Origin of Species by Natural Selection | 12 Non-Inheritance of Acquired Characters | 13 Human Inheritance | Figures


Morgan, T. H. (1925). Evolution and genetics. Princeton: Princeton University Press.

Cite this page: Hill, M.A. (2019, August 21) Embryology Morgan 1925 fig34.jpg. Retrieved from

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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