342 E. R. HOSKINS 



portion of the gland (fig. 8). The loose connective tissue among 

 the tubules contains numerous blood vessels. The lumen of 

 the gland is very irregular, the inner wall of the gland contain- 

 ing many pits and crypts into which the primary tubules open 

 individually and in groups of two to five. 



The duct, as before, is lined with high columnar granular 

 epithelial cells. Its surrounding covering is well differentiated 

 into connective tissue, smooth muscle and serosa, all of which 

 become continuous with the corresponding layers of the intes- 

 tine at the junction of the duct and gut. 



The peripheral ends of the tubules of the 200 mm. stage are 

 composed of cuboid or rounded cells with round nuclei. Toward 

 the central lumen the epithelium gradually increases in height, 

 becoming columnar in type, with elongated nuclei. The cyto- 

 plasm is finely granular, staining heavily with eosin. At the 

 mouths of the primary tubules the epithelium undergoes transi- 

 tion into the stratified type which lines the main central lumen 

 and central ends of the primary tubules. Where a primary 

 tubule opens directly through the main wall of the central lumen, 

 this change is very sudden, but where it opens into a pit in the 

 wall the transition is more gradual. The stratified epithelium 

 of the central lumen varies from two layers of cells in depres- 

 sions in the wall to four or five layers on the more exposed places. 

 Where the stratified epithelium is thick, the outer layer of cells 

 is composed of quite flat cells with rounded free surfaces, re- 

 sembling those seen in the urinary bladder of higher animals. 

 Their nuclei are flattened and lie with the long axis parallel 

 with the surface. The cells beneath the surface layer are for 

 the most part irregularly rounded, although some are columnar 

 and perpendicular to the inner surface of the gland. The for- 

 mer have round and the latter elongated oval nuclei. The 

 epithelium illustrates the law that a nucleus tends to assume 

 the shape of its cell. Here and there, in the surface layer of 

 epithelium, are large isolated goblet shaped cells which give 

 the customary reaction for mucus with Mallory's tri-color con- 

 nective tissue stain. The loose connective tissue among the 

 tubules is continuous with the dense layer in the capsule. The 

 smooth muscle is very definite in the capsule below the serosa. 



