INTEGUMENTAL GLANDS OF CROCODILIA 589 



Inside of this layer is the middle layer, composed of distinctly 

 larger cells, elongated in form and with distinct, heavy walls. 

 The nuclei of these cells often do not stain, so that the layer has 

 a clear appearance due to the absence of visible nuclei. The 

 inner layer, bordering the central cavity, is the thickest of the 

 three in most places. It is composed of large, irregularly spher- 

 ical or polyhedral cells, fairly sharply differentiated from the 

 middle layer. The cytoplasm is more scant and scattered than 

 in the other layers, and the nuclei ^re very variable in size, some 

 of them being large and spherical, others being less than half as 

 large and of a shrunken appearance. Next to the central cavity 

 these cells are quite irregular, with jagged edges as though they 

 were being torn off from the rest of the cell mass. 



Figure 18, A, represents a lateral view of a cloacal gland of an 

 80-cm. caiman, freed of the surrounding muscles and loose con- 

 nective tissue. It is retort-shaped with a maximum length of 

 1 cm. and a greatest width of 6 mm. The neck of the retort is, 

 of course, the duct of the gland. The gland actually shown in 

 figure 18, A, was cut sagittally and is shown in figures 19, 20, 

 and 21. The connective tissue covering the capsule over the 

 gland proper is compact and rather thin, but, as will be seen in 

 the description of the sections, around the duct it is a very thick, 

 rather loose mass, so that the diameter of the duct is not nearly so 

 great as it would appear in this surface view of the gland. 



Seen in sagittal section (fig. 19) or in transverse section (figs. 

 22, 23 and 24), the gland is found to contain a large lumen, per- 

 haps filled with secretion, which is eccentrically located and from 

 which the duct opens to the surface of the cloaca. 



Figure 19 represents a longitudinal section through the median 

 plane of the gland shown in surface view in figure 18, A. 



The duct, d, is cut almost exactly through its median plane and 

 shows on the right the complicated folds of its walls where it opens 

 to the surface. These folds or wrinkles resemble the more com- 

 plicated wrinkles seen in the duct of the mandibular gland, to be 

 described later, which seems to turn itself inside out. The wall 

 of the duct is composed of eight or ten compact layers of cells, 

 flattening out toward the lumen, where they form a thick layer 



