582 A. M. REESE 



The structure of the adult glands will be taken up after a 

 discussion of their development. 



The gland was first seen in an embryo of about 25-mm. crown- 

 rump length (fig. 2) as a rounded thickening and invagination 

 of the lower layer, stratum germinativum (fig. 3 and fig. 4, s). As 

 may be seen in figure 3, the gland lies somewhat above the level 

 of the dorsal side of the spinal cord, sc, and is relatively of large 

 size. It extends nearly through the dermis or corium, c, to the 

 outer edge of the underlying muscle, 7n. 



Under moderately high magnification the epidermis, at this 

 stage, is seen to consist of two layers, a very thin, outer layer or 

 periderm (Krause) (fig. 4, p) and a much thicker, inner layer or 

 stratum germinativum, s. Beneath the latter lies the very thick 

 and fairly compact and homogeneous layer, the corium, c. The 

 outer layer, p, exaggerated in distinctness in figure 4, is very thin 

 and contains flattened nuclei. The inner layer, s, is of somewhat 

 variable thickness and consists of one or two layers of polyhedral 

 or cuboidal cells; the nuclei of these cells are oval or spherical and 

 frequently lie at the base of the cells. 



The gland, g, at this stage consists, as has been said, of a 

 thickened invagination of the stratum germinativum. This 

 thickening consists (fig. 4, g) of a mass of indistinctly outlined 

 polyhedral cells, with large, spherical or oval nuclei. At the 

 fundus or inner end of the gland the cells are more closely 

 compacted than in the region nearer the surface. A wide invag- 

 ination, d, of both layers of the epidermis represents the position 

 of the future wide-mouthed duct of the embryonic gland. 



The next stage represented in figure 5, is taken from an em- 

 bryo of a total length of a little over 7 cm. The epidermis and 

 corium are here about as in the preceding stage, but the gland, 

 g, is much more elongated and now projects into the underlying 

 muscular tissue, m, as a bottle-shaped mass of cells, connected 

 with the superficial epidermis by a rather narrow neck. The 

 open invagination of the epidermis, d, is here deeper and narrower 

 than in the preceding stage. 



The cells of the gland have about the same appearance as 

 before, but they are distinctly less compactly arranged in the 



