"The whole of the mesoderm‥does not go through this metamorphosis, but‥a part remains closely compacted; but ultimately it is only the single layer of cells immediately bounding the cœlom, and the cells constituting the myotomes‥, which remain thus close together. These cells, therefore, have all the characteristics of an epithelium, so that the cœlom is limited by an epithelium of cuboidal cells, for which I have proposed the name mesothelium" (OED).