386 R. R. BENSLEY 



that Dewitt's observation is correct, and that there occur all 

 along the duct in the guinea pig large numbers of islets which are 

 directly connected to the duct, but have no connection with acinus 

 tissue. Thisisalsotrueforthedog,cat,rat, and rabbit. The series 

 of stages represented by these interstitial islets ranging from a 

 single cell through all gradations of size leave no room for doubt 

 that these islets are derived by direct growth from the ducts, and 

 that they are in a certain sense permanent organs of the pancreas, 

 for while it is probable that the cells of these organs go through 

 a certain series of cytomorphic changes ending in their death, 

 yet these islets have, in their duct connections, and in the undif- 

 ferentiated cells which form a part of them, the materials for 

 their own regeneration and repair. 



In discussing the large islets of the splenic end of the pancreas 

 in reptiles for which he admits a certain degree of permanency, 

 Laguesse explains this permanency by suggesting that it is only 

 relative, and that it is possible that these islets while permanent 

 as regards size and approximate location, may nevertheless be 

 constantly changing their substance by the inclusion of new acinus 

 tissue on one side while the islet may be changing into* acinus on 

 the other. Thus the islet is retained but its cellular material is 

 ever changing. The question, however, is not what is possible, 

 but what is true and I fail to find in Laguesse's discussion on this 

 topic any evidence that this process is actually going on. 



Another fact which it is impossible to reconcile with the hypoth- 

 esis of balance of Laguesse is the fact that the islets of Langer- 

 hans are unequally distributed in the pancreatic lobule. It is 

 well known, and is admitted by Laguesse, that the islets rarely 

 occur at the surface of the lobule. If Laguesse's hypothesis were 

 true, islets should be equally frequent in all parts of the lobule. 

 Laguesse sees in this fact merely an indication that acini in the 

 centre of the lobule have a greater tendency to undergo this change 

 than those on the surface, but this is merely stating the facts in 

 terms of his theory and is no explanation. 



On the contrary, a very simple explanation of this predilection 

 of islets for the central portions of lobules is possible when we 

 consider how the interstitial islets take their origin, and how the 



