Pix from this evening's lab...... we did get good gametes out of a few of the urchins, and got the processes of life to happen right before our eyes.
Here is a freshly fertilized sea urchin egg:
Here are fertilized eggs ready to undergo their very first division- the one at the very tip of the pointer is the best example. The "halo" around the egg is a specialized membrane, the clear spot in the center of the egg is the nucleus breaking down, and the "streak" appearance is the start of the first division:
Closeup of the first streak showing the first division:
Here's a whole group of dividing urchin eggs under low power- several of them have completed a first division:
This process took about an hour, and we could watch the division happen right before our eyes. I kept a slide of eggs that were fertilized during my first lab, and looked at them about 4 hours later. The egg continued to divide until it reached a stage called a gastrula:
The "hole" in the center is where cells are moving inward to form the urchin embryo's gut cavity. I tell this to my zoology students- what is so neat about this is that all animals undergo this process up to this stage! Urchins are a great model to look atbecause their developmental stages up to this point are about the same size as in humans. What's even cooler is that we got to see this entire process in the course of an evening.... right in front of us.