Today In Science History:
Kovalevsky was the Russian founder of comparative embryology and experimental histology. He established that there was a common pattern in the embryological development of all multicellular animals. He studied the tiny lancelet, a fish-shaped sea animal, then wrote Development of Amphioxus lanceolatus (1865).
In 1866, he demonstrated the similarity between Amphioxus and the larval stages of tunicates and established the chordate status of the tunicates. In 1867, Kovalevsky extended the germ layer concept of Christian Heinrich Pander and Karl Ernst von Baer to include the invertebrates, establishing an important embryologic unity in the animal kingdom.
The Amphioxus Song:
A fish-like thing appeared among the annelids one day.
It hadn't any parapods nor setae to display.
It hadn't any eyes nor jaws, nor ventral nervous cord,
But it had a lot of gill slits and it had a notochord.
It's a long way from Amphioxus. It's a long way to us.
It's a long way from Amphioxus to the meanest human cuss.
Well, it's goodbye to fins and gill slits, and it's welcome lungs and hair!
It's a long, long way from Amphioxus, but we all came from there.
The rest of the lyrics and the story behind the song Here