Fig. 2. Retinal dysplasia: four types of rosettes. A and B. Three-layer rosettes, which have the appearance of a mature retina secondarily thrown into folds. C. Two-layer rosette in which the innermost layer resembles a photoreceptor cell layer with an external limiting membrane and a relatively large lumen usually containing several undifferentiated cells. D and E. One-layer rosettes with a single layer of moderately well-differentiated neural cells, usually several cells in thickness, having an external limiting membrane-like structure surrounding the lumen. F. Primitive unilayer rosette in which a single layer of undifferentiated retinal cells surrounds the lumen with a tangle of fibrils centrally. (A, H&E, ×50; B, H&E, X200; C, H&E, X200; D, H&E, × 100; E, H&E, X 400; F, H&E, X 400)