78 Swale Vincent and F. D. Thompson. 



or central portion. At any rate we have never seen a mass of pan- 

 creatic tubules surrounded by a narrow ring of islet tissue: the reverse 

 seems always to be the case. 



There are also islets scattered along the portal vein. In this 

 species pancreatic tissue invades the liver to some extent, one or two 

 acini being frequently found in the peripheral parts of that organ, 

 and even in the interior. In the latter situation, however, they are 

 to be found almost exclusively in conjunction with blood vessels or bile 

 ducts. The pancreatic tissue seems in fact to have a tendency to 

 follow the portal canals into the substance of the liver. In the in- 

 trahepatic pancreas we have so far found no islets. 



Several observers, Massari^), Diamare"), and Rennie^) have de- 

 scribed a difference in the staining capacity of different areas within 

 the islets of teleosts. Diamare does not consider that this indicates 

 two distinct kinds of cells, but in many species Reunie found the 

 contrast in size, form, structure, arrangement, and relation to the 

 capillaries of the cells of the two regions of the islets so marked as 

 to induce him to hold the opposite view. We have not examined any 

 of the same species as Rennie selected, but so far as our observations 

 on this point go, we find that patches of different intensity of staining 

 do occur in the islets of Amiurus. The differences are however so slight 

 that we are not sure we should have noticed them had our attention 

 not be called to them by previous observers. The two kinds of cells are 

 shown much more clearly in the pigeon after inanition (PI. V, fig. 11, i.). 



In A. nigricans there is nothing which calls for a separate de- 

 scription, PI. V, fig. 17 is drawn from this species and not vulgaris. 



Moxostoma aureolum. No pancreas or islets found. 



Catostomus teres: In this si)ecies no pancreas was visible on 

 examination of the viscera, but on microscopical examination small 

 masses of pancreatic tissue were found in the capsule and portal 

 canals of the liver. Some of the cells in the acini weie stained very 

 deeply, and in some places no traces of a lumen could be found. 



') Rend. I!. A.rud. <lci IJiicfi. Vol. VII, i;isc. r>. |,. l;i4-i;J7, KS98. 

 "j I/or. «'it. 

 «) l.nc. (it. 



