How did Weismann’s germ plasm theory distinguish reproductive cells from body cells?

August Weismann’s germ plasm theory fundamentally distinguished between two types of biological material: the germ plasm and the somatoplasm (or soma).1

• Germ Plasm: This is the essential hereditary material found within germ cells (eggs and sperm). Weismann characterized this material as "immortal" because it is passed directly from one generation to the next, serving as the continuous physical basis of heredity.12
• Somatoplasm (Soma): This comprises all other cells of an organism—the body cells—that are not involved in reproduction. Unlike the germ plasm, the soma is not the vehicle for hereditary transmission.12

By establishing this clear separation, Weismann argued that changes acquired by the body cells during an individual's life cannot be passed on to offspring. This directly contradicted the Lamarckian theory of acquired characteristics, which suggested that traits developed by an organism could be inherited. Weismann’s distinction remains a cornerstone of modern genetics, emphasizing that hereditary information flows through the germ line rather than being influenced by the somatic experience.12