Pamphlets on Biology Volume 1431; Kofoid Collection (Paperback)


This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1921 Excerpt: ...region in Torpedo corresponds to that in S. acanthias." In the three Amphibian forms which Locr has studied (Amblystoma, Diemyctylus and Rana) "there are about ten pairs of segments in the broadly expanded neural folds of the head." In the chick "there are eleven segments in front of the first formed protovertebra." Locr has also found that in the chick "the walls of the primitive groove are divided into segments similiar to those which appear in the neural folds." My own observations in S. acanthias and Amblystoma differ from those of Loct and consequently my interpretation of his "neural segments" or "metameres" is different. In agreement with him I find the so called segments in the region of the cephalic plate most clearly marked in embryos with six to six and a half somites (a stage between Balfour's stages C and D). I find the "segments" confined to "marginal bands" along the edges of the neural plate. An examination of many embryos (more than fifty) at this most favorable stage leads me however to conclude that there is no constancy in the number of "segments" in different individuals and no agreement in number or position upon the two sides of the neural plate of a given individual. After a careful examination of a large number of embryos in this and very closely related stages (comprising more than two hundred and fifty individuals between Balfour's stages C and F), I have been compelled to abandon my earlier opinion, which was favorable to Loot's contention. In no case that I have seen do the segments appear symmetrical, and in no case have I been able to establish a definite relation with the somites. Locy believes that he has traced the "neural segments&quo...

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1921 Excerpt: ...region in Torpedo corresponds to that in S. acanthias." In the three Amphibian forms which Locr has studied (Amblystoma, Diemyctylus and Rana) "there are about ten pairs of segments in the broadly expanded neural folds of the head." In the chick "there are eleven segments in front of the first formed protovertebra." Locr has also found that in the chick "the walls of the primitive groove are divided into segments similiar to those which appear in the neural folds." My own observations in S. acanthias and Amblystoma differ from those of Loct and consequently my interpretation of his "neural segments" or "metameres" is different. In agreement with him I find the so called segments in the region of the cephalic plate most clearly marked in embryos with six to six and a half somites (a stage between Balfour's stages C and D). I find the "segments" confined to "marginal bands" along the edges of the neural plate. An examination of many embryos (more than fifty) at this most favorable stage leads me however to conclude that there is no constancy in the number of "segments" in different individuals and no agreement in number or position upon the two sides of the neural plate of a given individual. After a careful examination of a large number of embryos in this and very closely related stages (comprising more than two hundred and fifty individuals between Balfour's stages C and F), I have been compelled to abandon my earlier opinion, which was favorable to Loot's contention. In no case that I have seen do the segments appear symmetrical, and in no case have I been able to establish a definite relation with the somites. Locy believes that he has traced the "neural segments&quo...

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Product Details

General

Imprint

Rarebooksclub.com

Country of origin

United States

Release date

March 2012

Availability

Supplier out of stock. If you add this item to your wish list we will let you know when it becomes available.

First published

March 2012

Authors

Dimensions

246 x 189 x 5mm (L x W x T)

Format

Paperback - Trade

Pages

92

ISBN-13

978-1-130-15445-0

Barcode

9781130154450

Categories

LSN

1-130-15445-9



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