414 Bashford Dean Memorial Volume 



very close to the bursa entiana. In its natural position the dorsal pancreas tends to curl 

 around these organs, but in Text'figure 72 it (d.p.) is shown displaced to the left and spread 

 out flat. In my best'preserved specimen (No. I) the dorsal pancreas measures 45 x 25 

 X 2 mm. In my other specimens it is of approximately the same size, but is mutilated so 

 that precise measurements are impossible. A piece of the dorsal pancreas from specimen 

 No. I was removed for sectioning. Under the microscope the sections show, on one side, 

 alveoli characteristic of a pancreas, but I was unable to identify the ducts. Considering 

 that the material had been preserved for thirty years, the structure of the alveoli is 

 surprisingly well preserved. On the other side of each section I found areolar tissue, 

 blood vessels, cords of epithelioid cells and scattered epithelioid cells. This portion may 

 possibly represent an organ of internal secretion. 



In my specimens, the ventral pancreas is easily distinguished from the accessory 

 spleen, to which it is closely attached, by a difference in color: the ventral pancreas, 

 like the dorsal pancreas, is pale yellow, while the accessory spleen, like the spleen proper, 

 is very dark. Together, the ventral pancreas and the accessory spleen form a slender, 

 somewhat crescentic, slightly-flattened body whose approximate position is shown in 

 Text'figure 72 (v. p. and sp. 2). In specimen No. I this duplex organ is 40 mm. long 

 by 8 mm. wide at its widest level; in specimen No. II it is 70 mm. long by 10 mm. wide. 

 The ventral pancreas and the accessory spleen are of equal length and width, and are 

 united side-by-side; thus they appear as a single organ divided into two longitudinal 

 zones. From specimen No. I, segments were cut from the Hght zone and the dark zone 

 separately, and sections were prepared for microscopical examination. The light zone 

 was found to be in a very poor state of preservation, but is undoubtedly glandular. It 

 contains cords of epithelial cells, groups of cells which may represent alveoli, and cells 

 arranged so as to give the appearance of ducts; also scattered epitheHoid cells and many 

 small blood vessels. A fairly large artery runs along one side of each section. The 

 dark zone is in a much better state of preservation. It consists mainly of dense lymphoid 

 tissue containing a multitude of leucocytes and many extravascular erythrocytes. These 

 observations seem sufficient to identify the organ as a spleen. 



From specimen No. II a segment extending entirely across the duplex organ (ventral 

 pancreas and accessory spleen) was cut into transverse serial sections. The material 

 is in poor condition for histological study, but one side of each section is undoubtedly 

 pancreas, the other, spleen. Each organ has a connective tissue capsule. In places the 

 two organs are connected by their capsules, in other places the capsules are separated 

 by a cleft. 



So far as I know, this combination of a ventral pancreas with an accessory spleen 

 has not been observed in any other elasmo branch. In the teleost, Gamhusia patruelis, 

 the mingling of spleen and pancreas is described by Potter and Medlen (1935) from whose 

 paper I quote as follows: "The typical histological structure of this organ [the spleen] 

 is modified by the presence of pancreatic tissue. The pancreas is located in the mesen- 



