ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 329 



epithelium. Again, narrow duct-like or vesicular cavities appear quite frequently in 

 the epithelium, and terminate blindly in both directions. Further, I have seen a duct 

 bent like a U and opening at both ends into the lumen of the bile duct. Again, they 

 appear quite freely in parts of the bile duct outside the region of the supposed pancreas. 



The appearance presented by many of the vesicular cavities within the epithelium 

 of the bile duct is that of abortive evaginations. The cavity is surrounded by a layer 

 of non-glandular epithelial cells resembling those of the bile duct epithelium, and it 

 may or may not communicate with the lumen of the bile duct. Such structures are 

 commonly present in the centre of the lobules of the "pancreas." They give to those 

 parts of the bile duct where they occur the appearance of an epithelium of more than 

 one layer, and in any case it is not strictly unilaminar, as, for example, are the hepatic 

 ducts and the mucous membrane of the gut in this region. 



The free surface of the epithelium has a sharp cuticular edge, according to Maas, 

 and flakes off into the cavity of the duct. The cells also extrude a substance which 

 stains black with iron hsematoxylin. This material may in some cases be seen within 

 the cytoplasm of the epithelium, whilst the lumen of the duct itself is devoid of it. 



The nuclei of the epithelium of the bile duct are oval, clear, and vesicular, and 

 exhibit a reticular chromatin sometimes with, but often without, definite nucleoli. The 

 cells themselves have well-defined cell walls. 



7. The " Pancreas." 



In 1896 (37 and 38) Maas described what he called a pancreas-like organ in Myxine 

 and Bdellostoma/" He found, surrounding a portion of the bile duct, and also partly 

 embedded in the serosa of the gut, and somewhat more strongly developed in older 

 specimens, a peculiar glandular organ which he interprets provisionally as a pancreas. 

 He states that it may be recognised macroscopically, after the loose surrounding tissue 

 has been cleared away, as a yellowish white, lobulated envelope, which renders obscure 

 the course of the bile duct, and which cannot be removed without damage to the duct 

 and gut. It lies not symmetrically round the duct, but mostly on the left side, thus 

 diminishing on the side of the gall bladder. Near the opening of the bile duct into 

 the gut, however, the glandular mass forms a ring round the duct about equally 

 developed on all sides. It consists of a number of lobules, each of which is stated to 

 have a cavity in communication with the lumen of the bile duct. The secretion, then, 

 whatever its nature, would be discharged into the bile duct. 



The following notes must be regarded, not as a complete description of the 

 " pancreas " of Myxine, but as supplementing the descriptions of Maas. 



Counting the papilla within the lumen of the gut, the bile duct, from gall bladder 



* It seems quite possible that the structure described by Maas had already been discovered by Schneider in 

 1879. He says (49, pp. 95-6): "Uin die Miindung [of the bile duct in Myxine] liegen eine grosse Zahl von 

 Follikeln iihnlich wie bei Ammocotes." There is nothing but the "pancreas" in this neighbourhood to explain such 

 a passage. Maas quotes Schneider's work, but appears to have overlooked his statements relating to Myxine. 



