396 WALTER E. CAMP 



occur both in the gland cells and in the epithelium of the pharynx. 

 The mesenchyma surrounding the gland is still loose and scanty 

 except in the region between the vesicle and the pericardium, 

 where it is very dense and contains many nuclei, arranged 

 parallel to the surface of the pericardium. 



From the 47.3 mm. embryo up to the 'pup' stage (200 to 210 

 mm.) the increase in the number of the gland elements is very 

 great. In the 95 mm. embryo (H. E. C. 1882) the tubules have 

 become so numerous that the mesenchyma has been pushed 

 aside, leaving their epithelial walls in direct contact (figs. 7 and 

 26). The walls of three of the most dorsal tubules are fused with 

 the epithelium of the pharynx, but a distinct lumen through 

 the pharyngeal epithelium could not be traced. There is no 

 pit or indentation on the surface of the pharynx that would 

 lead one to suspect a communication. 



The process of secretion in the gland begins at a period prior 

 to the 'pup' stage (20-21 cm. in length). The exact time could 

 not be determined from the series of embryos at my disposal. 

 In the 95 mm. embryo (H. E. C. 1882) there are a few goblet 

 cells in the pharyngeal epithelium, but there is no evidence of 

 secretion in the gland. In a 'pup' 21 cm. in length many of the 

 cells, both of the gland tubules and of the pharyngeal epithelium,, 

 are actively secreting mucus. The smaller tubules are lined by 

 a single layer of narrow columnar cells with elongated oval or 

 rod-shaped nuclei in the basal portions. The larger tubules 

 have, in addition to the columnar cells, a layer of smaller flat- 

 tened cells lying next to the membrana propria. The mucous 

 secreting cells are rather numerous and are found in both layers. 

 The mucus may be located in either the free portion or the basal 

 portion of the cell. In some instances the secretion encircles 

 the nucleus and distends both the cuticula and the membrana 

 propria. The lumina of the tubules contain masses of secretion 

 of variable size in which are a few desquamated epithelial cells 

 and lymphocytes. 



As will be seen from the model shown in figure 27, the gland 

 is connected with the pharynx by a single elongated diverticu- 

 lum, extending obliquely from left to right, which is a direct 



