THE FUNCTIONAL PERIOD OF DEVELOPMENT 



5*i*-*^ •' »^' ♦^'-* 4 3«'-*» -V^l w^-^-w 



423 



m.g. 



'. ^c-y^^ 





S..V* 



f- 







B 



Fig. 205 



The effect of mechanical conditions on morphogenesis. In larval axolotls kept 

 out of water, the dorsal fin disappears. This is due to its falling over and becoming 

 fused with the skin of the back. A, Section of early stage of fusion. The meso- 

 dermal fin-axis {f.a.) is bent at the tip. B, Section of a stage showing complete 

 fusion. The fin-axis still shows a curved tip. The limit of the fused fin is 

 marked by a sudden thinning of the epidermis {ep.); bl.v. blood-vessel; vi.g. 

 mucous glands ; muse, muscles ; c.t. connective tissue. (From Huxley, Proc. Roy. 

 Soc. B, xcviii 1925.) 



