Final answer:
The member variable should be marked as protected to be accessible by subclasses and classes in the same package, but not by other external classes.
Step-by-step explanation:
To achieve the requirement that a member variable must be accessible by subclasses but not by classes which are not in the same package, the member variable should be marked as protected. This access modifier ensures that the member variable can be accessed by subclasses, regardless of the package they belong to, and also by classes in the same package, but not by other classes outside the package that are not subclasses.