98 



COMPARATIVE ANATOMY OF PANCREAS. 



of the Plaice, Fig. 10; the pancreas of the Stingray [Trygon sahina), Fig. 13; the 

 pancreas of the Hammerhead Shark {Zygoena malleus), Fig. 22; and the pancreas 

 of the Garfish (Lepisosteus osseus), Fig. 11. 



It matters not whether we view the pancreas in its earlier stages of development 

 in the higher animals or in its permanent condition in many of the Osseous Fishes, 

 its structure is the same. By classifying this organ according to its development 

 in fishes we have an exact history of the changes which occur during its development 

 in the higher animals. The permanent forms of the pancreas of the former are but 

 transitory conditions, forming the stages in the development of this organ in the 

 latter. According to Miiller, Weber, and Wharton Jones, in higher animals Avhich 

 have a perfect pancreas, its development, like that of the salivary glands, commences 

 by a simple diverticulum, or cascum, from the walls of the duodenum. This sub- 

 divides into bud-like processes. As the development of the gland advances, the 

 canal and its branches become more and more ramified and subdivided, until the 

 compound racemose lobulated gland is formed. Precisely the same stages of develop- 

 ment in a permanent form are discernible in the different orders, genera, and species 

 of fishes. 



Mere cells or follicular depressions in the mucous membrane of the small intes- 

 tines, according to the observations of Cuvier, Miiller, and Solly, perform the offices 

 of the pancreas in several species, as the Hippoglossm rondeletus, Conger Eel, Pike, 

 and Carp, and Opliisurus serpens. 



In the Ammodytes tohianus there is a single C£ecum prolonged into a pouch, repre- 

 senting this gland in its rudimentary condition. Several species of Plaice have two, 

 whilst others have three, like the River Perch and Common Loach, whilst the 

 Platessa ohlonga has four of these caecal pouches, which open into the pylorus and 

 duodenum. This form of the pancreas is seen in the following figure : — 



Fig. 10. 



Rudimentary pancreas of the Plaice {Platessa oblonga) reduced to one-half diameter. A. Stomach. B. Pyloric extre- 

 mity of stomach. C, C, C, C. Pancreatic casca opening into the small intestine below the pyloric valve of the 

 stomach. F. Small intestine. G. Large intestine. S. Spleen. 



Five of these caeca occur in Salmo spirlingulus, six in Perca lucioperca and 

 Sargus annularis, seven to eight in the Bass {Corvina ocellata), and ten to thirty 

 or more in many Salmons and Herrings, and from eighty to ninety in the Common 

 Salmon. 



