DEVELOPMENT OF THE ENAMEL 195 



interposed between, two sinusoids, and the secreted substance 

 is discharged into the lumen between the rows of secreting 

 cells. We thus see among the ductless glands a similar 

 arrangement to that found in the fish above described, 

 although this secretes some substance, the nature of which 

 is not known, into the brain cavity fluids. 



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O 2 



