A Microscopic Study of the Pancreas in Fishes; Especially Those of the Orders Haplomi and Cyprinodontes

Abstract

T HE existence of a relationship between the secretory function of the pancreas and pancreatic control of carbohydrate metabolism was demonstrated by the author in earlier publications and has been since confirmed by others: Boldyreff (1927, 1930, 1932, 1934), Coelho and Oliveria (1928), Okada, et al. (1928), Burge (1931). The wide variations in the amount and the distribution of glandular tissue, and the differences in arrangement of secretory cells in the pancreas of teleosts, as well as the variations in the structure of the gland as a whole in this group of vertebrates, offer an interesting field of study and may serve as a source of information concerning the relation of pancreatic structure to the functional activity of this organ. These considerations served as a starting point for the present investigation. The final selection of Esox, Umbra and Fundulus was made at the suggestion of Prof. Carl L. Hubbs at the University of Michigan, who was interested in these studies from the phylogenetic point of view. Esox and Umbra are known to be closely related; these fishes are also known to be definitely carnivorous (Adams and Hankinson, 1928). The alleged relation of Fundulus to the pikes has never been firmly established and has recently been questioned by Hubbs and others (see below). According to Linton (1901), the alimentary canals of Fundulus are usually filled with vegetable matter; therefore it may be concluded that the animal is largely vegetarian. Brunelli (1928) published an article dealing with the physiology and anatomy of the pancreas and liver in fishes. This author's contention was that there are two functionally different types of liver in fishes: (1) the hepatopancreas, present in those feeding on carbohydrate food (including mollusks), and containing large amounts of glycogen; (2) livers free from invasion by pancreatic tissue, which mainly store oil, and which are characteristic of carniverous fishes. Brunelli was inclined to believe that the presence of pancreatic tissue within the liver has a functional significance-the internal secretion of the pancreas may greatly facilitate the storage of glycogen. It is worthy of note, however, that the hepatopancreas organs of the fishes described in this report were found to be devoid of islet tissue.