Spotted Salamanders, Ambystoma maculata, lay eggs in February and March, often laying as a group, resulting in masses of egg masses. On March 16, 2015, one egg mass from one such mass laying was placed in an aquarium for observation. Using amphibians as an easy way to observe embryos isn’t new. The larvae returned to the pond after they were of a reasonable size. The following vocabulary is not official, but is demonstrative. Seriously, there is no pistachio stage in embryonic development. But they sure as hell look like brown pistachios.
The spotted salamander embryos begin to grow. They started as undifferentiated balls. They were probably laid on March 14, 2015, so this photo is only a few days after conception. On March 14 they were simple black balls you can see something is going on, what with them being a bit mottled. Although that may just be algae.
A few days later and the embryos have entered the pistachio stage. As in backbones. Okay, no backbones yet, but you can see them forming in a pistachio like manner. This seems to be called “neutralization”. But that is up to debate due to the writer’s embryology research failings. At four days on March 18, the embryos have developed a top and a bottom. They were little undifferentiated balls a few days ago, so this occurred within four days. The fatter, bulbous end of the fold on the embryo will be the head.
Starting to look like little commas. At 7 days, these salamanders definitely have a top and bottom and look like some kine animal. They are also very hard to photograph through egg goo.
Ten days old, and definitely slugs. The tail end is sort of pointy, and the head end is becoming flat. They are maybe three millimeters long. They can hatch at thirty days, depending on conditions, so could be a third of the way along.