Experiment 10: Study of T.S. of Blastula Through a Permanent Slide

AIM

Study of T.S. of blastula through permanent slide.

PRINCIPLE

Blastula is early embryonic stage formed after repeated cleavage divisions of zygote. In mammals it is called blastocyst with outer trophoblast and inner cell mass enclosing fluid filled blastocoel cavity.

Trophoblast forms placenta and protective covering while inner cell mass forms embryo proper. Zona pellucida surrounds blastocyst initially and hatches before implantation in uterus.

Study of transverse section under microscope helps to identify embryonic and abembryonic poles, trophoblast layer and blastocoel. This stage is crucial for implantation and further development of mammalian embryo.

REQUIREMENTS

• Permanent slide of T.S. of blastula
• Compound microscope
• Lens cleaning fluid and paper
• Pencil and eraser

PROCEDURE

1. Select a good prepared slide of T.S. of blastula and focus under 10x magnification under light microscope.
2. Now, study the structures and draw the different layers of cells seen.
3. And finally compare these structures with the labelled diagrams given ahead and identify them accordingly.

OBSERVATION

The transverse section of blastula shows the following features:

• It is a spherical mass of cells.
• The outermost layer, i.e. zona pellucida followed by a layer of trophoblast is clearly seen.
• Within the envelope, a fluid filled cavity called blastocoel is commonly found.
• Mass of cells inner to the trophoblast is called inner cell mass. Inner mass cells form the embryo.
• The blastocyst has embryonic or animal pole which is found opposite to the abembryonic pole.

RESULT

The transverse section of blastula clearly shows all the characteristic features of blastula stage of a mammal.

CONCLUSION

Blastula is spherical mass with outer zona pellucida, trophoblast layer, inner cell mass and fluid filled blastocoel. Presence of embryonic and abembryonic poles confirms mammalian blastocyst stage and its role in implantation and embryogenesis.

PRECAUTIONS

• Objective and eye lenses should be cleaned before viewing the slide.
• The slide should be centrally placed so that it can be focused properly under the low and high powers of compound microscope in order to enhance the clear visibility of all cells.