Darwin didn't have a specific term for individuals expressing mutations. This is because Darwin's theory of evolution by natural selection predates the understanding of genetics and mutations.

Here's why:

* Darwin focused on variation: Darwin observed that individuals within a species varied in traits. He called this "variation" and focused on how these variations affected an individual's ability to survive and reproduce.

* Mutations were unknown: The concept of mutations as a source of variation wasn't discovered until later, with the work of Gregor Mendel and others in the field of genetics.

Therefore, while Darwin recognized the importance of variation for evolution, he didn't have a specific term for individuals with mutations. This understanding came later with the development of genetics and the modern synthesis of evolutionary theory.