184 organisers: inducers of differentiation 



epidermal tissue which would normally not have given rise to a 

 lens at all. This can be effected either by grafting the eye-cup under 



y f 



h 



Fig. 88 



Self-differentiation of the lens in Rana esculent a. a, Extirpation of the pre- 

 sumptive eye-rudiment at the early neurula stage, b. Transverse section through 

 resulting larva 14 days after operation; in spite of the absence of an eye-cup, a 

 lens (L.) has developed by self-differentiation, c, This lens, at the same scale as 

 d, normal eye and lens, for comparison. (From Mangold, Ergehn. der Biol, vii, 

 1 93 1, after Spemann.) 



