T. Thomson Flynn and the monotreme egg from oocyte maturation to germ layer formation

Anthony M. Carter*

*Kontaktforfatter for dette arbejde

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Abstrakt

Knowledge of oocyte development and the early differentiation of the germ layers in monotremes stems largely from two articles by J. P. Hill and T. Thomson Flynn. The completeness of their account was due to the large series of echidna ovaries and eggs collected on Tasmania by Flynn, an Australian biologist of whom a brief account is given. A striking finding in the oocyte and early embryo of monotremes was the presence of a latebra connected to the yolk bed beneath the germinal disc as described in birds and several reptiles. A further resemblance was the presence early in vitellogenesis of a striate zone beneath the zona pellucida. Cleavage resulted first in a lens‐shaped blastodisc encircled by cells called vitellocytes that later fused to form a germ‐ring. The blastodisc gave rise to a blastoderm that eventually became unilaminar but comprised two cell types identified as ectoderm and primitive endoderm. Eventually these segregated into two layers and formed a blastula. This sequence resembled that in marsupials except there was no obvious distinction between future embryonic and extra‐embryonic regions. As the blastoderm extended over the surface of the yolk, it was preceded by the germ‐ring that eventually played a role in forming the yolk navel. This was a unique feature of monotreme development. It is shown that Flynn played an important role in analysis of the material as well as in its collection.
OriginalsprogEngelsk
TidsskriftJournal of Morphology
Vol/bind282
Udgave nummer7
Sider (fra-til)1015-1023
ISSN0362-2525
DOI
StatusUdgivet - jul. 2021

Bibliografisk note

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© 2021 Wiley Periodicals LLC

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

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