111 PANCKEAS 191 



(original left) respectively to the opening of the bile-duct, while the 

 dorsal opening is situated at the extremity of the spout-like pyloric 

 valve. 



The general course of development in Lepidosiren is similar and 

 in both it is characteristic that the pancreas never bul^-s ln-yond the 

 mesodermal coating of the splanchnopleure. It remains embedded 

 throughout life in the gut-wall and is consequently not noticeable in 

 an ordinary dissect inn. 



In Ceratodus (Neumayr, 1904) the development of the pancreas 

 is similar though here the left ventral rudiment, which in Protopterus 

 is smaller in size than the right, remains rudimentary. 



The Amphibia are of special interest from the fact that it was 

 a member of this group (JBombinator) in which Goette (1875) first 

 observed the origin of the pancreas from three separate rudiments. 

 Goeppert (1891) was able to extend the observation to various other 

 Amphibians, both Urodele and Anuran, and to show that in Urodeles 

 the dorsal rudiment retains its duct, opening just behind the pylorus, 

 while in the Anura this duct disappears. In both cases the ducts of 

 the two ventral rudiments undergo fusion to form a duct of Wirsung 

 which opens into the bile-duct. 



In Keptiles (Lacerta Brachet, 1896) the right ventral and the 

 dorsal rudiments fuse to form the definitive pancreas, the left 

 ventral atrophying (cf. Lung-fishes). According to Brachet the 

 duct of the dorsal rudiment does not disappear but fuses with that 

 of the right ventral to form the definitive pancreatic duct. 



Birds show three rudiments which undergo fusion into a complex 

 in the normal fashion, all three ducts remaining functional and 

 conspicuous in the adult. Suppression of the left ventral rudiment 

 occurs as an occasional variation. 



The observed facts of development of the Pancreas clearly justify 

 the conclusion that this organ of the modern Vertebrate has arisen 

 in the course of evolution from three originally separate diverticula 

 of the glandular enteric wall a pair arising from the hepatic pouch 

 and the third from the dorsal wall. The precise localization of the 

 rudiments at comparatively distant points of the enteric wall point 

 to the probability that the nature of the secretion was originally 

 different in the case of the ventral pancreas from that of the dorsal. 



PYLORIC CAECA. The caeca which are present in the pyloric 

 region in many actinopterygian fishes arise as simple outgrowths of 

 the gut-wall. The interesting suggestion has been made (Taylor, 

 1913) that the simple circle of these caeca, which is apparently their 

 most primitive arrangement, corresponds morphologically with the 

 curious valve found in various fishes (Amia, Lung- fishes, Symbranchus, 

 Anguilla, etc.) in which the pyloric end of the stomach is prolonged 

 back into a kind of spout which is ensheathed by the anterior end of 

 the intestine. The circular prolongation forward of the intestinal 

 cavity round the gastric spout might clearly give rise to a circle of 

 pyloric caeca simply by subdivision into a number of separate 



