594 A. M. EEESE 



able to say. The evaginated cells are of a dark, brownish-gray 

 color. When cut from the animal the musk gland, even when 

 the inner cells are evaginated, is seen to project beneath the 

 inner surface of the skin as a smooth, oval mass of considerable 

 size, to be described in connection with the adult animal. 



The mandibular musk gland is first seen in embryos of about 

 25 mm. crown-rump length (fig. 2). A vertical section through 

 the lower jaw of such an embryo is shown in fig. 32. The 

 glands are here seen, mg, as wide-mouthed pits formed by the 

 invagination of the ectoderm on either side of the midventral 

 line. The ectoderm increases in thickness from one layer of 

 cells over the general surface to three or four layers at the bottom 

 of the invagination. The pit is here about 1/10 mm. wide 

 and 4/10 mm. long. A slightly denser area of mesoblast is seen 

 around the bottom of each invagination, possibly the first 

 indication of the capsule of the gland. 



Figure 33 represents one of the gland invaginations of an 

 embryo of about the same size, but slightly more developed, 

 drawn under a greater magnification. The invagination is here 

 deeper and proportionately narrower than in the preceding 

 stage. Its bottom or fundus is distinctly enlarged and bulb- 

 like, 7ng, and the rest of the invagination forms what might now 

 be called the duct, d. The walls of the duct are of varying 

 thickness and consist of two or three indistinct layers of cells. 

 The fundus has a fairly distinct wall of several layers of elongated 

 cells and a central mass of somewhat scattered and irregularly 

 arranged cells. Surrounding the gland is a distinct area of 

 condensed mesoblast, cp. Several small blood vessels are seen, 

 scattered through the mesoblast. Along the dorsal edge of the 

 lower jaw at this stage may be seen numerous somewhat smaller 

 and solid invaginations of ectoderm, quite similar to the one 

 just described; these are the rudiments of the teeth. 



Figure 34, from a transverse section through a slightly older 

 embryo, shows but little advance over the preceding stage. The 

 fundus of the gland, mg, is shown distinct from the duct, d, owing 

 to the plane of the section. The entire gland is larger in size 

 and the surrounding condensation of mesoblast, cy, is more 



