SummaryAn example of a prepatellar cyst lined by stratified epithelium is described. An opinion that this is an epidermal cyst or tumour depends on an acceptance of the three germ‐layer hypothesis, which would imply that stratified epithelium, especially if squamous, is necessarily of ectodermal origin.The problem of the specificity of the germ layers is examined briefly from the general biological viewpoint. Although it is not possible to do more than indicate in a very sketchy way the, main points (biological details of species, etcetera, are not given), an indication of the breadth of the question and the great volume of investigation is provided. The experimental work is discussed and some of the pathological observations are mentioned. From whichever of these viewpoints the question is considered, it is apparent that the germ‐layer hypothesis is largely phantasy.That there are three layers to be seen at certain stages of development of some animals (particularly those with large egg yolks 1 has been abundantly demonstrated, but it has been shewn that any a priori opinion that a condition such as that described here must be epidermal (that is ectodermal in origin) is unjustified. In normal conditions the three layers are separate and evolve in a usual, apparently predetermined fashion, but in “thunder, lightning or in rain (that is, in pathological states) they show a disregard for boundaries that is the more complete the more they are studied in such circumstances.The variations in form of the synovial membrane of bursae are shown in several examples. The specimen described here is one in which a hidden potentiality is exposed a growth capacity of which synovial membrane is capable in abnormal conditions the development of a stratified and squamous epith