74 Swale Vincent and F. D. Thompson, 



D. Amphibians. 



Islets of Langerlians have been described in amphibians by many 

 observers, more particularly by v. Ebner ^), Diamare-), and Dale-'). 

 The leptochrome islets, corresponding to those in other groups of 

 animals, have been fully described by these authors, particularly the 

 last-named, who employed chiefly toads for his observations. 



Our own work has so far been confined to the trog, and an 

 American newt, Plethodon glutinosus. In the case of the frog we 

 desire in the first place to call special attention to obvious tran- 

 sition forms between leptochrome islet and zymogenous tissue (see 

 PL V, fig. 13 and PI. V, fig. 14, U-cms. c). In many sections, the 

 limits of the inlets cannot be assigned with any definiteness with the 

 low power of the microscope, and with the high power this is fre- 

 quently almost impossible. 



There are, moreover, in some parts of the section, branching 

 columns of cells, which stain much more deeply than other regions. 

 These clearly correspond to the bathychrome tissue previously described 

 in higher vertebrata (see Pi. V, fig. 13, hath, t.), so that in amphibians 

 also we have to deal with two distinct structures, not counting the 

 ordinaiy zymogenous parenchyma of the pancreas. Thus, in a section 

 of the frog's pancreas, stained by one of the ordinary methods, there 

 are three kinds of structure visible, the medium-stained groundwork 

 of secreting tubules, the leptochrome islets, and the bathychrome cell 

 columns (PI. V, fig. 13). Some of the bathychrome columns have cells 

 coiresponding in position to the centro-acinar cells of the zymogenous 

 tubules. Scattered thi'oughout the section, too, one can see small 

 groups or even isolated cells giving the bathychrome reaction. In the 

 bathychrome tissue are the same highly refractive cells above described 

 in similar situations in bii'ds and reptiles (see pp. 9, 10 and 11). 



Some of the islets in the trog are of a unique structure; they 

 consist of spherical or sausage-shaped masses of cells, staining more 



') Arch. f. mikr. AiK.t. Hd. S, S. 481. 1872. 

 «) Lor,, (if. 

 '; Lor., cif. 



