- In non-keratinized stratified squamous epithelium, the key characteristic is the absence of keratinization, which distinguishes it from keratinized epithelium found in areas exposed to high friction, such as the skin.

- The stratum granulosum is a layer in keratinized epithelium that contains granules of keratohyalin, essential for the formation of the tough, protective keratin layer.
- This layer is responsible for initiating the process of keratinization, leading to the formation of the stratum corneum, the outermost dead cell layer.

- In non-keratinized epithelium (e.g., lining of the oral cavity, esophagus, and vagina), the stratum granulosum is missing because these epithelia retain their nuclei and remain alive at the surface, and they do not produce keratin granules.
- The layers that remain include the stratum basale, responsible for cell proliferation, and the stratum spinosum, providing structural support through desmosomal connections.

Hence, the correct answer is the stratum granulosum, as this layer is absent in non-keratinized stratified squamous epithelium due to the lack of keratin production.

Key points:
- Non-keratinized epithelium lacks the stratum granulosum.
- Stratum granulosum contains keratohyalin granules necessary for keratinization.
- Non-keratinized epithelium remains moist and nuclei persist in surface cells.
- Stratum basale and stratum spinosum layers are present in both keratinized and non-keratinized epithelia.

Reference: Junqueira's Basic Histology, 14th Edition, Chapter 4, Page 67