584 A. M. KEESE 



deferred to later stages; they are evidently not yet functioning, 

 and ^yould not be expected to function this long before hatching. 



The dorsal gland of a 15-cm. embryo is shown in figure 9, 

 as drawn with a camera under medium magnification. The 

 .epidermis, ep, here exhibits two well-defined areas; the above- 

 mentioned periderm, which now shows clearly, under high 

 powers, as a fibrillar or scaly structure, and the stratum germi- 

 nativum, s, from which the gland has been developed, as described 

 above. In the stratum germinativum, as as well as in the 

 immediately subjacent corium, c, may be seen numerous brownish 

 pigment bodies of irregular shape and size. 



In the region of the duct, d, which lies in the longitudinal 

 groove between two scales, the corium is considerably thickened. 

 In the particular section here shown the opening of the gland to 

 the surface, is not shown and in fact, this gland did not show 

 any opening at all, the periderm being uninterrupted. In other 

 series a break in the periderm was visible and an irregular 

 opening through the thickened area of the stratum germinativum 

 could be made out. There is, however, quite a sharp line of 

 demarkation between the closely packed mass of cells of the 

 stratum germinativum, that forms the apparent duct of the 

 gland, and the more loosely arranged, less deeply staining cells 

 of the gland proper. While the gland proper is now several times 

 larger than it w^as at the preceding stage, the duct is relatively 

 and actually considerably narrower and shorter. 



The gland, as may be seen in figures 1 and 9, is circular in out- 

 line and is flattened until its dorsoventral thickness is about 

 one-half its diameter. It lies almost entirely below the corium, c, 

 and is surrounded by a thin connective-tissue capsule, cp. It 

 consists of a fairly compact peripheral mass of cells, which 

 become looser and more scattered towards the center (fig. 9). 

 These cells are finely granular and have such indistinct walls that 

 their boundaries can only with great difficulty be determined; 

 they contain oval or round nuclei. Around the periphery of the 

 gland, next to what may be called the basement membrane, is a 

 fairly distinct row of nuclei, representing an indistinct layer of 

 basilar cells, (figs. 9 and 10, b) ; passing from these cells towards 



