Each bud arises as a thickening of the epithelium, which.
This process may result in a considerable thickening of the thallus.
The lower part of the free edge of every mesentery, whether complete or incomplete, is thrown into numerous puckers or folds, and is furnished with a glandular thickening known as a mesenterial filament.
The nuchal skeleton is a non-cellular laminated thickening of basement-membrane underlying that portion of the stomochord which lies between the above-mentioned pouches and the orifice into the throat.
It is best to commence the electrolytic thickening in a silver acetate bath.