^28 Charles R. Stockard 



ical influence exerts a peculiar inhibition of that process of out- 

 pushing or separation by which the optic vesicles arise. Such an 

 idea will be more fully considered in the general discussion given 

 below. 



The unequal eyes may possibly result from an unequal allotment 

 of eye material to one side or the other. A major portion might go 

 to the right side and a minor part to the left, or the entire eye an- 

 lagen might by chance occur on one side. This in a sense would 

 be lateral cyclopia. Such reasoning is of course purely hypothet- 

 ical. 



INDEPENDENT ORIGIN AND SELF-DIFFERENTIATION OF THE 

 CRYSTALLINE LENS 



Spemann ('oi), Lewis ('04), and others have concluded from 

 experiments on amphibian embryos that there is no localization of 

 lens-forming material in any given area of the ectoderm. They 

 further held that the formation of a lens is dependent upon a stim- 

 ulation of the ectoderm through contact with the optic-vesicle or 

 cup. Spemann ('05) in discussing the question of the self-dif- 

 ferentiating power of the lens concluded from a consideration of 

 Schaper's ('04) experiments on the frog that the lens is not capable 

 of self-differentiation, but that a continued influence or contact 

 of the optic-cup is necessary to cause the lens-plate or lens-bud 

 to develop into a typical lens. LeCron ('07) has recently shown 

 that the lens in Amblystoma is not self-diff'erentiating. I ('o/d) 

 found in embryos of the blind Myxinoid, Bdellostoma stouti, that 

 a lens-thickening formed in early stages while the optic-vesicles 

 were near the ectoderm. During development the optic cup 

 becomes distantly removed from the ectoderm and the lens-plate 

 disappears as if it were unable to continue development independ- 

 ently of the optic cup contact. 



On the other hand Mencl ('03) has claimed that the lens in 

 Salmo salar is at times formed independently of the optic cup 

 influence and Spemann ('07) has recently modified his attitude. 

 Spemann finds that in a certain species of frog, Rana esculenta, 

 the lens may arise independently of the optic cup. This lens also 



