With the help of replicas and pseudoreplicas (unstained and stained) of the corneal endothelium in numerous mammals many pit-like endothelial islets, which are lighter after staining, can be found. They appear only in the most peripheral zone of the cornea. They consist of flatter cells than the surrounding endothelium but they are surrounded by a higher circular hem. The surface of the islet cells does not show a regular secretory activity of viscous substance production. It shows rather a fine granulation. Considering the transitions of the islets into surrounding endothelium and their development and mass appearance in some sectors, while they are missing in others, we assume that they are transitory formations which are formed by the surrounding endothelium ad hoc and change back again into it. The flattening of the endothelium in the islets can hardly be explained in any other way than by the action of intraocular pressure on the cells or by the decrease of their cytoplasma. This would be possible in those places where the uniform cuticle has been disturbed by depolymerizing enzymes. The intact cuticle would prevent the flattening of the endothelial cells. In this case we could regard the islets as the place of production of depolymerizing enzymes. Then we would have to assume that mammals, in which according to species or even young age the islets are missing, this task is fulfilled by endothelial cells which are dispersed in the endothelium and produce alternately one or the other material.
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