Beobachtungen über die Befruchtung und Entwicklung des Kaninchens and Meerschweinchens.

Hensen's node. "Hensen’s research focused on the embryonic development of guinea pigs and rabbits. While studying those organisms he noticed something previously undiscovered—an enlarged area above the primitive streak. He referred to that area as the node in his article, “Beobachtungen uber die Befruchtung und Entwicklung des Kaninchens and Meerschweinchens” (Observations on the fertilization and development of the rabbit and guinea pig). Hensen’s article was meant to describe development and encourage other researchers to further investigate the node. After the article, people researched nodes, and in 1924 Hans Spemann and Hilde Mangold published their work on the node in African clawed frogs (Xenopus laevis), for which they called the node the organizer. Hensen’s node and the organizer have nearly the same characteristics—in both chick and frog embryos they become the head processes. Kupffer’s vesicle which was later discovered in fish is also similar to the organizer and Hensen’s node" (https://embryo.asu.edu/pages/hensens-node).