Embryos 'R Us
After 33 years of researching insect embryos, you'd think that I'd have had my fill of them. And yes, I thought I had. That is, until I discovered the lacewing embryo.
I touched on these in a recent blog, where I looked at the larvae of these insects hatching from the egg. My photos of the embryos on that occasion weren't very clear because of the chorion, a milky white membrane that surrounds the egg.
A few days ago I discovered another clutch of lacewing eggs, laid on the fly screen of our dining room window. This time I was able to get better photos of the embryos inside - either by clearing the chorion with a dilute bleach solution (an old trick I used to use with Drosophila embryos), or by removing it with fine forceps (gratified to discover I can still do this).
Anyway, here are my mugshots of lacewing embryos taken over a five day period.
Day 1 (probably a couple of days after fertilisation)
View from the ventral (belly) side. Head is up. The paired roundish blobs at the top end are the rudiments of the antennae and mouthparts. The egg is 1mm long.
Same embryo viewed from the other side. The rear end of the embryo curls around the bottom of the egg and continues on this side.
Day 2
The rudiments of the walking legs have now developed - 3 pairs of pigmented, elongated structures pointing towards the embryo's midline.
A side view of the embryo (above) reveals its head lobes curling around the top of the egg and the tail curling around the bottom. The embryo sits on top of a mass of white yolk.
Day 3
A ventral view shows that both the mouthparts and walking legs have grown longer. The flanks of the embryo are strongly pigmented.
A view from the back shows the end of the embryo curling around the bottom of the egg. The mass of yolk on which it sits is clear to see.
Day 4
The antennae and 3 pairs of mouthparts are now much longer and the legs are looking more like the real deal. I'm not sure what the white cellular skirt around the bottom of the embryo is - research topic!
A side view of the embryo shows that the flanks have grown and cover more of the yolk.
Day 5
A further increase in length of the antennae, mouthparts and legs. The embryo is not far off hatching. Such a pretty thing!
A side view of the same embryo reveals one of its pair of eyes. Each consists of just six visual units, called ommatidia. Adult insects typically have eyes with thousands of ommatidia. The rear end of the embryo now curls forwards and lies just beneath the limbs. Tightly packed in there!
The same embryo viewed from the back shows that its flanks have grown around the yolk and fused to form a complete body tube. The yolk is now contained within the embryonic gut. This will nourish the larva for the first day or so after hatching. The dark line down the dorsal midline is the developing heart.
Life after the egg
This clutch of eggs will probably hatch tonight and I want to get this blog posted now. So here is a shot from my earlier blog of the larva immediately after it has broken free of its embryonic home. Ahh, room to move!