GAS-SECRETING TISSUES 



337 



which parts before the pressure and closes again when the bubble has 

 passed. 



The cytology of the typical gas cells is peculiar. As this is more 

 easily seen in those of some other fish than the cod, we shall examine 

 them in the swim-bladder of the 

 golden paradise fish, or so-called Jap- 

 anese goldfish (Fig. 300). This tis- 

 sue has been described by Reis and 

 Nusbaum. 



In this form the differentiation of 

 a distinct gland is but partial, the 

 thick heavy gas cells lining the entire 

 interior of the swim-bladder, and 

 being invaginated to some degree on 

 an area of the ventral surface only. 

 Here the few tubular imaginations 

 extend down into the connective tis- 

 sue lying between the epithelium and 

 the wall of the swim-bladder. 



Cells taken from any part of the 

 gas epithelium will answer. Such 

 a cell is cylindrical with its base rest- 

 ing on a blood channel and its distal 



end touching the lumen of the bladder or one of its branches in the lu- 

 mina. Its base is somewhat thickened and stains deeper owing to 

 materials placed here that do not occur elsewhere. These materials, 

 which at best can be only identified as fine granules amid a network of 

 irregular fibrils, are either some particular organ of the cytoplasm that 

 is used to collect the gas-forming materials from the blood, or they repre- 

 sent those collected materials themselves. A combination of both con- 

 ditions is the best explanation of this appearance. 



These materials must certainly be passed forward through the cyto- 

 plasm of the cell as fluids or as very fine granules. This can safely be 

 assumed, yet no trace of their presence is visible until we have gone distad 

 of the nucleus in our search, and come to the outer third of the cell. Here 

 the materials for the making of the gas are once more to be seen, collected 

 as granules in an important organ of the cell, a series of fine cytoplasmic 

 channels that gather at their center into a central cleft of irregular out- 

 line. The lumen of this channel system is not free but filled with another 

 and more fluid form of cytoplasm. The cytoplasm of this region elabo- 

 rates the materials into the gas or into granules of substances that readily 

 combine to form the gas, and these granules are passed down the channels 

 to the cleft. In this space they are converted into the gas mixture which 



FIG. 300. Five gas-secreting cells from 

 the gas gland in the swim-bladder of the 

 paradise fish, Macropodus viridi-auratus. 

 b., thickened distal border of the cells 

 on the lumen; vac., gas-vacuoles ; tr., 

 trophospongia; bl.ca., capillary. (After 

 REIS and NUSBAUM.) 



