THE FUNCTIONAL PERIOD OF DEVELOPMENT 



435 



tube connected with the bladder, large quantities of a neutral fluid 

 can be introduced into it, with the result that its internal pressure 



^'n 





':i 





/ 



U:l 



V. 



» 



0^ 



'i^!to^. 



^ 



Fig. 212 



Functional activity and morpho- 

 genesis in amphibian gills. Below: 

 two salamander larvae; left, reared 

 in conditions of oxygen-deficiency 

 (in water under an atmosphere with 

 II per cent. Oo) ; the gills are long 

 and feathery; right, reared in con- 

 ditions of oxygen-excess (in water 

 under an atmosphere of pure O2) ; 

 the gills are short and stumpy. 

 Above : sections of gill-filaments 

 from two similar larvae; right, 

 oxygen-deficiency : epithelium one 

 layer thick, of flattened cells ; left, 

 oxygen-excess : epithelium often two 

 layers thick, of rounded cells. (From 

 L. Drastich,Zeif5c/;r./. vergl. Physiol. 

 II, 1925.) 



is raised. The quantity of fluid evacuated per day may reach 

 50 litres under these experimental conditions. As a result of this 

 increased work to which the wall of the bladder has been put, it 



28-2 



