The yolk is a spherical mass, of a pale yellow color, lying in the center of the white. Its diameter is so great that it lies very close to the shell around the lesser circumference of the egg, so that it is there covered by only a thin layer of white, and care must be taken in removing the shell from this region in order not to rupture the yolk. The yolk substance is quite fluid and is contained in a rather delicate vitelline membrane. The albumen and yolk of the crocodile’s egg, as described by Voeltzkow, differ from those of the alligator only in the color of the albumen, which in the crocodile is _normally_ light green (78). As pointed out by Clarke, the position of the embryo upon the yolk is subject to some variation. During the earliest stages it may occur at the pole of the yolk nearest the side of the egg; later it may generally be found toward the end of the egg; and still later it shifts its position to the side of the egg. It is probable, as Clarke says, that the position at the end of the egg secures better protection by the greater amount of white, at that point, between the yolk and the shell; while the later removal to the side of the egg, when the vascular area and the allantois begin to function, secures a better aëration of the blood of the embryo. Around the embryo, during the stages that precede the formation of the vascular area, is seen an irregular area of a lighter color and a mottled appearance. This area is bounded by a distinct, narrow, white line, and varies in size from perhaps a square centimeter to one third the surface of the yolk. During the earliest stages of development the embryo is very transparent; so that, as there is no fixed place upon the yolk at which it may be expected to occur, it is often very difficult to find. Owing to this transparency, to the extreme delicacy of the embryo, and to the character of the white, the removal of an early embryo from the egg of the alligator is a difficult operation and is accomplished only after some practice. THE DEVELOPMENT OF THE EMBRYO As the writer has pointed out elsewhere (59), the embryo of the alligator is often of considerable size when the egg is laid. This makes the obtaining of the earliest stages of development a difficult matter; so that the writer, as has already been said, like S. F. Clarke (17), made three trips to the South in quest of the desired material. Voeltzkow (78) experienced the same difficulty in his work on the crocodile, and made several trips to Africa before he succeeded in obtaining all the desired stages of development.