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Developmental Biology Lab Practical Study Guide

Sea urchin slides

Unfertilized eggs – The vitelline envelop is apparent.

Fertilized eggs – The fertilization envelop is further away from the egg then the vitelline envelop in an unfertilized egg.

Early cleavage – Different embryos consist of different number of cells.  Know that cleavage in sea urchins is holoblastic and why cleavage is holoblastic.

Blastula – sea urchin embryos in the blastula stage have an outer ring of cells and a hollow blastoceol.  The cells that make up the blastula are called blastomeres.

Starfish slides

Blastula – The same as that of the sea urchin blastula.

Gastrula – This stage embryo contains the primitive gut (archenteron).  The opening of the archenteron at the vegetal pole is called the blastopore.

Frog slides

Cleavage – Frog embryos in the cleavage stage produce different size cells.  This is due to the fact that cleavage is impeded in the yolky vegetal hemisphere.  Be able to indicate that frog cleavage is holoblastic.

Blastula – Frog embryo that contains a blastoceol located in the animal hemisphere of the embryo.

Early gastrula – The early gastrula is beginning to form the archenteron at the marginal zone of the embryo.  You should be able to distinguish the difference between the archenteron and the blastoceol of a frog embryo in the early gastrula stage.

Yolk plug – Identify the yolk plug.  You should also be able to identify the archenteron and the remnants of the blastopore.  The archenteron will be nearer the yolk plug and much bigger then the blastocoel at this stage of frog embryogenesis.

Neural groove – A frog embryo that contains a neural groove is in the neurula stage.  The neurula stage begins organogenesis in a frog embryo.  You should also be able to identify the archenteron of a frog embryo in the neurula stage.

Chick slides

18 hour, wm – A chick embryo at 18 hours has already formed the primitive streak that is not fully formed.  This means that the primitive streak is still elongating towards the anterior portion of the embryo.  The anterior end of the primitive streak is called Henson’s node.

24 hour, wm – By 24 hours, the primitive streak is beginning to regress.  Anterior to the primitive streak, the embryo is undergoing organogenesis.  In addition to identifying the primitive streak, you should be able to identify the head folds (early formation of the head), the neural folds and the somites.

33 hour, wm – By 33 hours, the primitive streak has regressed even further towards the posterior portion of the embryo.  There are many more somites in a 33 hour embryo compared to that of a 24 hour embryo.

48 hour, wm – By 48 hours, the primitive streak has regressed to the posterior portion of the embryo and consists basically of Henson’s node.  A 48 hour embryo has a well-defined ventricle of the heart.