On the Relations between the „Islets of Langerhans" etc. 69 



the mouse tliey are large and abimdant. In all three, transition forms 

 are frequently encountered. 



B. Birds. 



In birds we find in abundance the bathychrome and leptochrome 

 tissues already mentioned as occurring in mammals. 

 Pigeon. 



In the pancreas of the pigeon the splenic end is characterized by 

 a number of large islets which are almost absent at the opposite end 

 of the gland. These islets are easily recognised as such, being lighter 

 in tint in stained preparations than the surrounding zymogenous tissue 

 and in fact presenting all the main characteristics of islet tissue in 

 mammals (see PI. IV, fig. 7, PI. V, fig. 9, PI. V, fig. 10, lept t, i). 

 Transitions between these leptochrome islets and zymogenous tissue are 

 striking and fi-equent (PI. IV, fig 7 and PI. V, fig. 9, trans, c). 



The bathychrome tissue is represented by solid masses of cells of 

 a very deep tinge in stained preparations (PI. IV, fig. 7, PI. IV, fig. 8, 

 PI. V, fig. 9, hath, t., hath. c. and hath. syn.). In specimens stained 

 with haematoxylin and eosin, these form deep blue irregular branching 

 and anastomosing columns of cells, sometimes forming extensive areas, 

 at other times being constituted by one or two cells, and occasionally 

 are seen scattered individual cells of the same type (PI. IV, fig. 7 and 

 PL V, fig. 9, hath, t., hath. c. and hath. syn.). 



With the low power the protoplasm of this tissue seems almost 

 homogeneous, but with a high power it may be recognised as presenting 

 a curious mottled appearance (PI. IV, fig. 8, hath. syn.). It has occurred 

 to us that these may be none other than the „cellules troubles" of Laguesse, 

 and constitute the „primary islets" of this author, while the pale 

 (leptochrome) islets previously described are his „secondary islets". 

 We are, however, very far from being satisfied upon this point, because 

 nowhere can we find in his writings or eleswhere, any statement of 

 such a striking difference in appearance and constitution between the 

 two kinds of islets. 



The three stiuctures, zymogenous tubules, leptochrome islets, and 

 the bathychrome tissue form a very striking picture in the pancreas 



