524 Experimental Studies on the Origin of the Lens in Amphibia 



of lens formation or even before the adhesion of the optic vesicle and 

 skin. This adhesion takes place before there are any visible signs of 

 epithelial differentiation for the lens. In nine other similarly performed 

 experiments of this series the eye remained deeply buried for periods of 

 5 to 12 days after the grafting without sign of lens formation. 



In the three following experiments of series XI, performed in the 

 same manner as experiment Xl^g, one corner of the optic vesicle came in 

 contact with the skin and a lens has developed between the optic vesicle 

 and the skin at this place. 



Fig. 30. Experiment XI30. Section through rig-ht optic cup and lens, s, sylvatica. 

 p, palustris, a, region of the overlapping of the skin of Rana sylvatica by that of 

 Rana palustris. n, nasal pit. X 75 diameters. 



Experiment XI^o. 



The embryo of experiment XI32 was killed 5 days after the operation. 

 One corner of the optic cup has reached the surface near the nasal pit 

 at about the junction of the skin of E. palustris with that of E. sylvatica 

 (see Fig. 30). A small lens about 70 micro mm. in diameter lies 

 between the optic cup and skin and probably has arisen from the skin 

 of E. palustris close to the nasal pit. The normal lens on the left side 

 measures about 100 micro mm. in diameter. 



Experiment XI^q. 



As in experiments Xl^g and XI32 the head end of a E. sylvatica em- 

 bryo was grafted onto the right side of the head of a E. palustris from 

 which the skin had been carefully torn off. At first the optic vesicle 

 was deep beneath the graft and could be seen projecting into the dis- 

 tended coelom of the E. sylvatica, see Fig. 31. Eight days after the 

 operation the tadpole was killed. One corner of the somewhat irregular 

 optic cup was found to approach near the skin at about the junction of 

 the abdomen of E. sylvatica and E. palustris and near to the nasal pit 



