| Summary: | 1. In Whales variations in the thickness of the baleen plates are supposed to give an insight into certain cyclical processes in the life of the animal. To a certain extent, by means of these variations, it is possible to reach conclusions about the age of the animal and/or about its recent period of life.\nIn order to get a better insight in the significance of the variations in thickness of the baleen plate, researches are made in the histogenesis of the baleen plate of Fin Whales and Blue Whales, caught in the Antarctic waters. The variations in thickness are caused by variations in thickness of the cortex of the baleen plate. 2. The \xe2\x80\x9croot\xe2\x80\x9d of the baleen plate consists of the following parts: the corium wall, the epithelium that covers the corium wall, the cortex and the epithelium of the gum. 3. In the epithelium of the gum arched bands of varying width are visible. These bands run into the outer layer of the cortex. There is a correlation between the width of these bands and the height of the thickenings of the cortex, in which they end. These bands are not present in the epithelium that covers the corium wall. In both epithelia corium papillae are found. On the top of each papilla a row of spherical cells is formed. In the epithelium that covers the corium wall these rows of spherical cells all run into the cortex and there they cannot be distinguished from the surrounding cornified material. This is also correct for the very few rows of spherical cells originating from the corium papillae near the base of the corium wall. These rows run into the first band of flattened cells of the gum. They become flattened with the cells of the stratum spinosum of the gum in this band, forming the very first layer of the cortex. The other rows of spherical cells in the gum, even those immediately adjacent to the cortex, all run parallel to each other and to the outer surface of the cortex. They never run into the cortex. This shows clearly that the cell material of the gum forms the first and outer ...
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