**Core Concept**
Coccidioides immitis is a fungal pathogen that causes coccidioidomycosis, a disease primarily affecting the lungs. When inhaled, the fungus undergoes transformation to form a characteristic structure in tissue.

**Why the Correct Answer is Right**
Coccidioides immitis produces spherules in tissue, which are large, thick-walled structures containing endospores. The spherules are formed when the inhaled arthroconidia transform into a spherical shape, allowing the fungus to grow and multiply within the host's tissues. This transformation is a key virulence factor, enabling the fungus to evade the host's immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** The term "hyphae" refers to branching, filamentous structures characteristic of many fungi, but not Coccidioides immitis in tissue.
**Option B:** "Arthroconidia" are indeed a stage in the life cycle of Coccidioides immitis, but they are not the structure produced in tissue.
**Option C:** "Endospores" are contained within the spherules formed by Coccidioides immitis, but they are not the structure itself.

**Clinical Pearl / High-Yield Fact**
Coccidioides immitis is a dimorphic fungus, meaning it can exist in two distinct forms: as arthroconidia in the environment and as spherules in tissue. This dimorphism is crucial for its pathogenesis and underscores the importance of understanding the fungus's life cycle in diagnosing and treating coccidioidomycosis.

**Correct Answer:** D. Spherules