On the Relations between the „Islets of Langerhans " etc. 79 



Hyodon alosoides. A large ^nd definite pancreas was found behind 

 the Jivej-, with large and nunieious islets. Some of these, being stained 

 very lightly, stand out prominently in the section; others, though clearly 

 recognisable as islets, approximate in depth of tint to the zymogenous 

 tissue, producing in fact an appearance similar to what one might 

 expect, if over a restricted area of the section there had been some hin- 

 drance to the staining process. All intermediate forms are to be found. 



The more highly developed islets are composed of solid columns 

 of cells, irregular in size, branching and anastomosing and very irre- 

 gular in diameter. The interspaces between the columns are occupied 

 by a rich capillaiy network. The tissue of the islet is freqtiently in 

 direct continuity with that of the zymogenous pancreas, and may often 

 be seen to shade off gradually into it. The islet columns are composed 

 of two kinds of cells, dark and light, as described by previous observers. 



In the zymogenous tissue occasional very darkly staining (bathy- 

 chrome) cells are present as in many other species. 



Esox litcius. The pancreas has the same position as in some of 

 the higher vertebrates, lying along the first fold of tlie intestine. The 

 gland is much encroached upon by adipose tissue. Islets on the whole 

 are infrequent, but comparatively large, and show some striking tian- 

 sitions (PI IV, fig-. 18, trans, c). 



Stizostedium vitreum. With the naked eye no tiace of pancreas 

 could be found. Although bits of pancreas were discovered micro- 

 scopically in the liver, no islets could be found. 



S. canadense. No definite pancreas was foun4 on naked-eye 

 examination, but little whitish bodies were scattered along the portal 

 vein. Under the microscope these bodies were seen to consist of islet 

 and zymogenous tissue, mixed with a large quantity of fat and con- 

 nective tissue. One islet was very much larger than any of the others, 

 definitely encapstiled, and having septa of connective tissue running 

 into its interio!'. Much of the zymogenous tissue was also encapsuled, 

 but mostly in very small packets. No clear examples of transition 

 from one tissue to the other could be made out.^). 



') The zymogenous tissue, although recognisable in a general way as such, 

 especially under a low power, presents several peculiar features. In some of the 



