DEVELOPMENT OF THE LENS 



55 



A piece of presumptive brain region from a Triton larva at the mid- 

 gastrula stage was grafted into another Triton embryo at the same stage 

 of development. The graft developed by self-differentiation into parts 

 of the brain and an optic cup. This induced the formation of a lens from 





pw~9 



r n. 



Fig. 40. 



-Dependence of the Development of the Lens on the Presence of 

 the Optic Cup. 



A — Triton larva into which a piece of presumptive brain region was grafted from 

 another embryo of the same age. g. : graft which developed by self- 

 differentiation into parts of the brain and an optic cup, which induced the 

 formation of a lens /. from epidermis derived from the abdominal region of 

 the host. 



B — Transverse section through the same larva, showing the vesicle produced from 

 the tissue of the host, v. ; a portion of the grafted brain, br. ; the optic cup, 

 op. c, derived from grafted tissue ; sp. c. : spinal cord ; and pr. n. : 

 pronephric tubules. 



(After O. Mangold, from Elements of Experimental Embryology : Huxley and de 



Beer.) 



epidermis which was continuous with that covering the ventral part of the 

 trunk of the host. 1 



2. Self differentiation. — The same author describes independent 

 differentiation of the lens in Rana esculenta after extirpation of the pre- 

 sumptive eye rudiment at the early neurula stage (Fig. 41). The drawing 

 1 O. Mangold (193 1), Ergebn. der Biol, 7, after Spemann. 



