526 Experimental Studies on the Origin of the Lens in Amphibia 



shape and size of the lens would indicate that it was formed soon after 

 operation and that subsequent growth and shifting of the eye or of the 

 graft or of both brought the eye to lie in the position seen in Fig. 15. 

 The irregular shape of the lens with a long process extending out 

 through the pupil and then bending towards the skin seems to me in- 

 dicative of such shifting, and a pulling away of the lens from its original 

 position just beneath the skin. This lens is about the same diameter as 

 the normal one on the left side. 



Series XII. 



In the experiments of series XII a small piece of skin from the abdo- 

 men of E. sylvatica was grafted onto the side of the head of E. palustris. 

 As in series XI the skin over the side of the head of E. palustris of 

 stage II was first torn off, leaving the optic vesicle and structures about 

 exposed. Onto this denuded area a thin piece of skin from the abdo- 

 men of a slightly older E. sylvatica was grafted. Very thin pieces of 

 skin with scarcely more than the epidermis were found almost impossible 

 to use, as they immediately rolled up into little balls before one could 

 transfer them to the E. palustris.. So it was necessary to include a 

 little of the underlying mesenchyme. In most of the experiments the 

 mesenchyme was too thick and prevented the underlying optic vesicle 

 from reaching the ectoderm and in such experiments no lens was 

 formed. 



Experiment XII^^. 



The, tadpole of this experiment was killed 7 days after the operation. 

 Fig. 34 shows a lateral view of the tadpole with the irregular mass 

 on the right side of the head. This mass is the grafted-on piece of the 

 abdomen of E. sylvatica. I was not able to determine before section- 

 ing whether the optic vesicle had been in contact with the skin. The 

 sections, however, show an irregular optic cup beneath the skin of E. syl- 

 vatica. The. skin of E. sylvatica extends on the left from the point a to h, 

 see Fig. 35. One corner of the optic cup is superficial and between 

 it and the ectoderm is a small lens about 90 micro mm. in diameter, see 

 Fig. 36. The normal one on the left side is about 160 micro mm. in 

 diameter. It is evident that the lens must have come from the ectoderm 

 overlying the optic cup, and consequently from ectoderm from the 

 abdomen of E. sylvatica. We have here then the optic vesicle of E. 

 palustris stimulating the lens formation from the skin from the abdo- 

 men of an animal of a different species. This is not more than might 

 be expected when we consider how perfect are the unions between the 



