242 



THE MOSAIC STAGE OF DIFFERENTIATION 



for although the presumptive neural fold region has been much 

 reduced in the head-region, some of it is still present, and this 



Fig. 119 



Power of regulation in differentiation and growth of the eyes in Triton, a, Opera- 

 tion performed at the early neurula stage : a piece of the presumptive eye-region is 

 removed without interfering with the underlying tissues. Z>, Resulting larva 

 17 days after operation; left eye normal, right eye 1/3 normal size, c, The same 

 animal just metamorphosed, 103 days after operation; both eyes approximately 

 normal and equal-sized. (From Mangold, Ergebn. der Biol, vii, 1931.) 



remnant has undergone regulation and has differentiated into a 



complete and normally formed brain with its attendant structures.^ 



On the other hand, the overprovided embryos also regulate to 



^ Spemann and Bautzmann, 1927. 



