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H. D. REED 



that of the growth of cartilage from the stylus out upon the mem- 

 brane of the fenestra. Growth is confined entirely to the dorsal 

 side of the stylus and its tip end. A comparison of figures 15 

 and 16 illustrate this point. In the former is the very beginning 



Fig. 16^ Transection through the fenestra vestibuli of an embryo Amphiuma 

 means 30 mm. long, but more advanced than that from which figure 15 was drawn. 

 vlc.,(arteria carotis interna; Col., stylus columellae (columella) spreading slightly 

 over the outer surface of the fenestral membrane; Ec, ear capsule; Fe.m., fenes- 

 tral membrane; Sq., squamosum; V.p.L, vena petrosolateralis. 



of this growth^ where, in the section sketched, only one cell is 

 shown pushing out* toward the membrane. Figure 16, which is 

 more advanced, shows that the diameter of the stylus is much 

 increased, all of which is due to the extension of its own substance 

 over the surface of the membrane. To what extent the fenestral 



