What aspect of the Marine Corps emblem was modified by General Jacob Zeilin?

General Jacob Zeilin significantly modified the design structure of the Marine Corps emblem during his tenure as the 7th Commandant of the Marine Corps in the 19th century. His changes transitioned the emblem to include the eagle, globe, and anchor, which have become iconic symbols of the Marine Corps. Zeilin’s modifications helped establish a clearer representation of the Marine Corps' identity, distinguishing it from other branches of the military at the time.

The choice of design structure is correct as it encompasses the visual elements and arrangement that make up the emblem, which is foundational to its identity and recognizable status today. This was not just a matter of aesthetics but also of deeper significance, as the eagle represents the nation, the globe signifies the worldwide presence of the Corps, and the anchor reflects its naval ties.

The other aspects listed, such as symbolic meaning, color scheme, and overall size, while they may have changed over the years, are not the primary focus of General Zeilin’s modifications. His work primarily concerned the emblem's structural design, which laid the groundwork for the symbolism that would follow.