First up, a sea urchin embryo, from George Watchmaker at Livermore, CA, USA.
Sea urchins were one of the first model systems in developmental biology, and the first species in which sperm cells were shown to fertilise the ovum! Nowadays they're often used by groups doing evolution and development (evo-devo) studies.
Now for the second picture: this time, it's a human!
This embryo is just starting to grow limbs, you can see one of the limb buds as a big blob coming off the side of the embryo. Even now, when it looks like a shapeless blob, the limb already has all three axes determined: dorsal-ventral (back to palm of hand), anterior-posterior (thumb to pinky - even though the digits haven't yet formed!) and proximal-distal (shoulder to fingertip). I'll write a more detailed post on limb development (and what can go wrong) sometime in the future, because it's a really great example of organ development in an embryo.
I hope everyone had a great Christmas! I can't believe it's almost 2010. I have to start thinking about my New Year's resolutions... eek
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