338 HISTOLOGY 



appears as a number of tiny bubbles that unite to form larger vesicles. 

 These latter work to the surface of the gland or inner surface of the swim- 

 bladder and are discharged into it. 



When the gas is formed, there is a residual material that remains 

 as a mass of solid granules that are discharged with or after the gas. 

 This is a by-product of the chemical processes by which the gas was 

 formed. 



The entire mucosa in the cod is divided into a large number of 

 lobules that take an independent origin from the basal tissues. Between 

 these lobules the epithelium with its underlying connective tissue is 

 evaginated into a series of folds that rise above and cover over with their 

 edges the lobule, forming in this way a common covering for the entire 

 organ, but leaving openings through which the gas may escape into the 

 bladder. 



This covering is thus lined on both its upper and its lower surfaces 

 with the undifferentiated lining epithelium of the swim-bladder, and the 

 central layer is composed of a connective tissue of fine texture in which 

 run arteries and veins. The meaning of the structure is not plain, and 

 requires further study. It allows the gas to escape from the gland by 

 the parting of the sticky edges of its several parts, which then drop back 

 into place. 



Technic. There are no special methods which have been evolved 

 for the purpose of bringing out any of the specific features of the gas 

 epithelium of the gas gland. Flemming's fluid and Zenker's fluid serve 

 to fix the tissues so that all the known structures may be seen when the 

 sections have been stained in iron haematoxylin. 



LITERATURE 



SCHNEIDER, K. C. "Histologie," Jena, 1904, S. 599. 



REIS, C., und NUSBAUM, J. "Zur Histologie der Gasdriise und s. w.," Anal. Anz., Band 



XXVII, S. 129, 1905. 

 NUSBAUM, JOSEPH. "Zur Histologie der tatigen Gasdruse und des Ovals bei den Teleos- 



tiern.," Anal. Anz., Band XXXI, Nr. 6. 



