Cutting the Vitelline Membrane

For right-handed operators (reverse for left-handers) (Fig. 2):

1. Place yolk with blastoderm facing east.

2. Hold yolk with coarse forceps at west pole, and cut with larger pair of scissors around the equator or just below it, starting south and moving north, keeping an eye on the position of the blastoderm at all times.

3. When cut right around, take both pairs of watchmaker's forceps and lift vi-telline membrane lightly at the cut edge. Position yolk so that blastoderm is on top, facing the operator.

4. Hold the edge of the vitelline membrane with both pairs of forceps, and pull very slowly by inverting it over the yolk, keeping the membrane low over the yolk, and pulling towards the bottom of the dish (see Note 7). Stage 4 and 5 blastoderms adhere fairly well to the vitelline membrane and are easy to handle. Older and younger blastoderms need more care.

5. When the vitelline membrane is freed from the yolk and the blastoderm still attached to it, immerse a watch glass into the BSS and pull the membrane onto it (see Note 8). As you raise the watch glass above the BSS level, hold onto the membrane with tweezers or it will float off.

6. Place the watch glass with the blastoderm in a 90-mm Petri dish.

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