STUDIES ON THE PANCREAS OF THE GUINEA PIG 371 



first sight to contain both sorts of granules. On the contrary, 

 there are abundant examples of cells which might be fairly con- 

 sidered as intermediate between the clear cells of the islet and the 

 A cells. Accordingly, as far as my evidence goes I am obliged 

 to conclude that the two types of islet cell are independent and 

 that each develops from an undifferentiated duct cell. 



3. The structure of the epithelium of the intralovular ducts and the 



centroacinous cells 



The third type of epithelial cell involved in the discussion of 

 transitions between islets and acini is the epithelial cell of the small 

 duct. A description of this type has already been given in dis- 

 cussing the structure of the small tubules which connect the ducts 

 with one another and which give rise to interstitial islets. Here, 

 it is simply necessary to emphasize the differences between the 

 cells of the ducts and those of the acini and islets. 



From the acinus cell the duct cell differs in the fact that it pos- 

 sesses neither basal basophile substance nor zymogen granules, 

 and also by the fact that it possesses an elongated oval nucleus 

 which, by comparison with the acinus cell, is relatively poor in 

 chromatin. 



From the islet cells of both types the duct cell differs in the fact 

 that it is totally devoid of the characteristic granules of the islet 

 cells. 



The mitochondria of the duct cell is unusually abundant, which 

 is quite in accord with what we would expect in view of the high 

 developmental potency of the duct cell. In fact the cells of the 

 smaller ducts when stained for mitochondria, resemble closely the 

 embryonic cells described by Meves ('08), inasmuch as the only 

 formed elements visible in them are thick mitochondrial rods 

 (chondrioconts). 



The cells of the terminal ductules including the centroacinus 

 cells are richer in fuchsinophile bodies than the cells of the larger 

 intralobular ducts (fig. 14). Much of this fuchsinophile material 

 is in the form of the characteristic mitochondrial rods, but, in 

 addition there are irregular spherical or angular granules present 



