350 E. R. HOSKINS 



Signs of degeneration were noted in various sections of the 

 adult digitiform gland. Elongated cysts was found in the paren- 

 chyma. These apparently are formed from occlusion of the 

 proximal part of tubules. They contain a substance which 

 gives a mucous reaction to Mallory's connective tissue stain. 

 They are bounded by a single layer of flat cells. A number of 

 the cells in the parenchyma contain small vacuoles. Some of 

 the surface cells in the central lumen, although having the shape 

 of mucous goblet cells, contain large granules which stain red 

 instead of the usual blue with Mallory's stain, and are colored 

 red in hematoxylin and eosin preparations. In places the nuclei 

 in the surface cells appear pyknotic. 



Summary of Part 1 



The digitiform gland appears in embryos of Squalus acanthias 

 of 15 mm. in length as a general outpouching upon the right 

 dorso-lateral side of the gut about midway between the pos- 

 terior end of the spiral valve and the beginning of the cloaca. 

 This anlage rapidly takes the form of a hollow bud which grows 

 first toward the right then turns and grows anteriorly. 



As the digitiform gland moves away from the intestine it 

 carries with it the common mesentery, thereby leaving this 

 part of the gut free in the body cavity, forming the 'mesenteric 

 fenestra' between the intestine and dorsal wall of the body 

 cavity. 



The young gland forms outpouching^ which extend laterally, 

 at right angles to its longitudinal axis, and which resemble in 

 form the original gland anlage. These outpouchings become the 

 primary tubules and in turn give off secondary tubules. 



By repeated subdivisions as many as six orders of tubules 

 may be formed. The manner of tubule formation is unique. 

 A primary tubule may extend unbranched to the periphery; it 

 may divide dichotomously near the central lumen ; it may extend 

 nearly to the periphery, giving off several tubules at right angles 

 to its long axis, but at irregular intervals, or, lastly, it may end 

 near the central lumen, dividing suddenly into a cluster of as 



