Secrion IV., 1907. [ 275 ] Trans. R. S. C. 
XVIII.—The Islets of Langerhans and the Zymogenous Tubules in the 
Vertebrate Pancreas, with special reference to the Pancreas of 
the Lower Vetebrates. 
By SwaLe Vincent, M.D. (Lond.), D.Sc. (Edin.) 
Professor of Physiology in the University of Manitoba. 
and 
FLORENCE D. THompson, University of Manitoba. 
(From the Physiological Laboratory, University of Manitoba.) 
(Communicated by Prof. A. B. Macallum, and read May 15, 1907.) 
In two recent communications! we have given what appeared to 
us very strong reasons for supporting the views of those who hold that 
the Islets of Langerhans cannot be regarded as in any sense a tissue 
sui generis. In the animals examined by us we found that the islets 
frequently show traces of a distinct alveolar arrangement. The islet 
columns are frequently in complete anatomical continuity with the 
surrounding zymogenous tubules, and all kinds of transition forms are 
common throughout vertebrates. In Reptiles and Fishes a distinct 
lumen within the islet area can sometimes be detected. 
In mammals (dogs and cats), birds (pigeons), and amphibians 
(frogs), the effect of inanition is to markedly increase the amount of 
the islet tissue at the expense of the zymogenous. In this condition 
direct continuity and transition forms are even more marked than in 
the normal animal. 
If, after a period of inanition, an animal be restored to its normal 
condition of nutrition, the pancreas likewise returns to the normal, and 
the presumption is that alveoli are reconstructed from islets. 
* An increase in the amount of islet tissue may be induced by 
exhausting the pancreas with secretin (confirmatory of Dale ?). 
In the islets of the pigeon after inanition and in the corresponding 
structures in teleostean fishes, we have observed two kinds of cells 
differing slightly though distinctly in their staining power (confirmatory 
of Diamare,? Rennie,* and others). 

1Journ. of Physiol. Vol. xxxiv (Proc. Physiol. Soc.), June 2, 1906. 
Internat. Monatsschr. f. Anat. u. Physiol., Bd. xxiv, 1907. 
2Phil. Trans., 1904. 
8 Quart. Journ. Micr. Sci., Vol. 48, Part III, Nov., 1904. 
4Internat. Monatsschr. f. Anat. u. Physiol, Bd. xvi, Heft. 7/8, 1899, 
u. Bd. xxii, Heft 4/6, 1905. 
