On the Relations between the „Islets of Langerhans" etc. 77 



one of the fundamental points in question, and since the species we have 

 examined have been for the most part quite different, it will be as 

 well for us to give a somewhat detailed description of our obser- 

 vations. 



Amiurus vulgaris. 



Macroscopic. There is nothing visible to the naked eye which 

 can be certainly described as pancreas. The position of the pancreas 

 in higher vertebrates is mapped out by a chain of small whitish specks. 

 There is a particularly large mass of opaque white stiucture some 

 Mttle distance anterior to the spleen. Tliere are also scattered bodies 

 of a similar appearance in the mesentery. On slicing through the 

 liver no trace of any tissue othei' than liver is to be found. 



Microscojnc. On examining the structures under the microscope 

 a very remarkable picture presents itself. The large mass near the 

 spleen is seen to be almost entirely composed of „islet" tissue, and 

 probably corresponds to Rennie's „principal islet". It is several milli- 

 raeteis in diameter, and permeated everywhere by capillaries which 

 roughly subdivide it into lobules. The whole is surrounded by a mixed 

 capsule of connective tissue and pancreatic (zymogenous) tubules. This 

 is of varying thickness at different parts of the circumference, and 

 the ah'eoli are arranged with their long axes concentrical to the cir- 

 cumference. In addition there are septa of the same mixed character, 

 conveying connective tissue, blood-vessels, and zymogenous tissue into 

 the interior of the huge islet (PI. V, fig. 17) where very frequently 

 there are large triangular or stellate masses of tubules, or broad, 

 irregular, branching and subdividing columns of the same tissue, sepa- 

 rating the islet into incomplete compartments of very varying shapes 

 (PI. V, fig. 17, 2ijm.). 



The chain of small specks is also composed for the most part of 

 islet tissue, but some of them consist of secreting tubes. Others again 

 consist of „islet"' tissue with an irregular ring ot zymogenous tissue 

 round them. The islets are frequently encapsuled, and this also applies 

 to separate masses of secreting tubules of various sizes. Whether the 

 islet tissue and zymogenous tissue which are in proximity occupy the 

 same capsule or not, it is always the islet which occupies the interior 



