Nereis under the Moonlight

On warm summer nights in the early 1890s, Wilson could frequently be found leaning over the docks of the MBL with a light and a net in either hand. Below him, Nereis worms would swarm at the surface of the water, females circling with numerous males close behind (Wilson 1892). Having arisen from the depths of Eel Pond to spawn at the surface, both fertile adults and eggs and sperm were easily collected. Once he had captured the worms, Wilson would hurry back to the lab where he would fertilize the eggs and follow their development throughout the night.

The main species Wilson studied, called Nereis limbata, is a bristle worm belonging to the class polychaeta (“many bristles”), which is the largest and most diverse class of annelids (Pearse and Buchsbaum 1987). For this species, surface swarming and spawning is seasonal and regulated by the lunar cycle, meaning fertile worms can only be collected on summer nights. Nereis proved to be an excellent species with which to study cell lineage because they produce large quantities of embryos and their cells are transparent, allowing observation of internal development and cell movement without having to fix and cut into the embryos. Back in the lab, once males and females are placed together in a dish and allowed to spawn, a single female will release thousands of eggs. Once the eggs are fertilized, a single squeeze of a pipette can pick up hundreds of embryos for examination. Furthermore, all of the embryos from a single spawning event will development more or less synchronously, allowing for thorough observation of each stage through comparison across several specimens.

The MBL proved an ideal location for Wilson’s work. Nereis were easily collected within steps of the laboratory throughout the summer, providing Wilson with an unlimited supply of embryos to carefully study cell divisions through early development. To this day, on clear summer nights, Nereis can still be collected from the MBL docks on Eel Pond. Just like Wilson in the 1890s, a lamp and hand net are all that is required to scoop up male and female worms and bring them back to the lab for study. Leaning over the side of the dock, eyes peeled and intensely focused on the illuminated surface of the water, it is easy to slip into Wilson’s shoes. Over a century later, these worms still rise to the surface when beckoned by the lamp to perform their mating dance, just like they did for Wilson and many others after him.