348 R. R. BENSLEY 



producing by (liffereiitiatioii, and by mitotic division, islets, acini, 

 and mucous glands. 



This function of producing islets, etc., is also shared by the 

 columnar cells of the ducts of the pancreas, for it is by division of 

 these that the tubules in question are being produced, and further- 

 more, islets, and acini in process of growth are related to these 

 ducts in precisely the same way as they are to the anastomosing 

 tubules which have just been described. The ducts of the gland- 

 like outgrowths which are found all along the pancreatic duct are 

 also composed in part of undifferentiated cells like those of the 

 duct and one may find islets or acini originating from these (fig. 6). 



As shown by the vital staining methods the islets of Langer- 

 hans of the guinea pig pancreas fall into the following categories: 



1. Islets unconnected with the acinus tissue, located in the 

 interstitial tissue of the pancreas, particularly along the duct and 

 its primary branches, and connected with the ducts either directly 

 by short ducts, or indirectly by means of the system of tubules 

 which has just been described. 



2. Islets located in the substance of the pancreatic lobules, 

 but wholly unconnected with the acini, and directly connected 

 with the interlobular duct system by shorter or longer branches. 



3. Islets located in the lobules of the pancreas, with the acini 

 or ducts or both of which they are in direct continuity. 



4. Islets unconnected with either acini or ducts. These may 

 be located either in the interstitial tissue or in the substance of 

 the lobules. Islets of this class belong primarily to 1 and 2, since 

 having originated from a duct they have lost this connection. 



The islets of class 1 are of all sizes, varying from single cells to 

 the largest islets of the pancreas. The mode of their attachment 

 to the ducts is well shown in figs. 4, 5, 7, and 8. As shown in fig. 

 7 many of these islets have multiple connections with ducts, in- 

 dicating that they have either originated by the fusion of several 

 islets of separate origin, or effected secondary, unions with the 

 duct system. In rare cases only does the lumen of the duct actu- 

 ally penetrate the substance of the islet, and in the few cases 

 where this does occur, as a rule, the proximal portion of the islet 

 into which the lumen extends is composed of duct cells, not of 



