_The Histology of the Integument._ To understand the structure of the integument of the Crocodilia it is well to begin with the embryo. A cross section of the epidermis of such an embryo will show the rete Malpighii as a single layer of short, cylindrical cells; over these are found more or less flattened, disk-shaped cells formed by transverse division of the underlying cells of the rete. On the outside lies the epitrichial layer which consists of a mosaic of polygonal cells, near the middle of each of which lies an oval nucleus. Between the epitrichial cells are small oval holes, not unlike the stomata in the epidermis of plant tissues. Bronn thinks these are not artifacts, but he does not suggest any explanation of their occurrence. In the epidermis of young and half-grown animals the rete Malpighii is seen still as above noted. On these cylindrical cells are found flattened cells that gradually become very flat and lose their nuclei as they pass over into the horny layer. The stratum corneum consists of strongly flattened cells in which the nuclei can no longer be clearly seen, though their location can usually be determined by the groups of pigment granules. On the cells of the more superficial layers of the stratum corneum are seen straight, dark lines, perhaps ridges caused by pressure of the over- or underlying polygonal cells. The individual cells of the horny layer are usually easily isolated in the belly and neck regions where they never become very thick; but in the back the cells in this layer are very numerous and fuse with each other to form the bony plates; here the rete is the only clearly differentiated layer. Whether prickle cells are present in the epidermis of the crocodile Bronn is not certain, though he thinks they probably are. Rathke pointed out that on the surface of certain folds of the integument, especially in the region of the jaws, are found in all Crocodilia certain small, scattered, wart-like elevations, around each of which is customarily a narrow, shallow, circular groove; they usually have a dark brown but sometimes a gray or even white color. Microscopic examination shows these warts to be of epidermal origin, consisting of bright, round cells that are closely united, without visible intercellular substance. Treatment with potassium hydroxid and then with water will show sometimes, though not always, fine granular nuclei in the cells.