The mammalian erythrocytes differ from the leucocytes at maturity because the erythrocytes are

The answer to the given question is "discoid and enucleated." Erythrocytes, commonly known as red blood cells, and leukocytes, also known as white blood cells, are two main types of blood cells. Erythrocytes are responsible for carrying oxygen to different parts of the body, while leukocytes are responsible for protecting the body from infection and disease. At maturity, erythrocytes lack a nucleus and other organelles. This allows them to carry more oxygen and have a flexible, discoid shape, which helps them to pass through narrow capillaries. On the other hand, leukocytes have a nucleus and are more flexible, amoeboid-shaped, which enables them to move and migrate in response to infections and injuries. Therefore, the correct answer is "discoid and enucleated."