292 LEIGH HOADI.hY. 



is not completely incorporated by the chorionic overgrowth. At 

 both ends of the sectioned material, where the stratum opticum is 

 cut nearly transversely, the nerve fibers of this layer show very 

 well. The whole graft compares \vry favorably with the normal 

 eye of the same age. 



In the experiments performed on the forty-eight hour chick, as 

 in those cited for the thirty-six hour material, the degree of 

 regulation seems to be dependent on the amount of injury to the 

 engrafted tissue, both during manipulation and during the growth 

 period which follows. My data show many cases where a much 

 convoluted retina and tapetum are present with no posterior 

 chamber showing. All degrees of lens malformation may occur. 

 The retinal cells are always definable as such, though the degree 

 of differentiation of the retina as expressed by zone formation 

 varies considerably. 



Five successful grafts were obtained from thirty-six hour pri- 

 mordia from which the lens ectoderm had been dissected away. 

 The data on these cases are to be found in table I. In only one of 



TABLE I. 



GROWTH OF THIRTY-SIX HOCR OPTIC VESICLES WITH THE LENS ECTODERM 



REMOVED. 



Case. Control Age. Remarks. 



15 A i 83 days Posterior chamber, retina and tapetum present. 



No lens tissue. 

 15 B i 8\ days Nervous tissue, cartilage, much convoluted retina, 



tapetum, small amount of lentoid tissue. 



15 C i 8 days Very little area of much convoluted retina and 



tapetum only. 



16 B i 8 days Nervous tissue, retina and tapetum. No lens 



tissue. 



16 B 2 8 days Cartilage, retina, much convoluted tapetum. No 



lens tissue. 



these grafts are any lens cells present. It is more reasonable to 

 suppose that these are the result of the proliferation of some cells 

 of the lens ectoderm which were not removed in the operation, 

 than that they arose by a redifferentiation of the cells of the 

 retina or iris (see Fischel for amphibian larva?, 1900) or by a stim- 

 ulation of the chorionic ectoderm by the optic cup (see Lewis i<i<>7 

 and Spemann 1912, and other papers on the amphibian <.-y(A 

 Spemann (1912), Lewis (1907 a, b, c,), and other w<>rkrr- have 



