396 PATTERNS AND PROBLEMS OF DEVELOPMENT 



to repeated experiment and various interpretations.^" This regeneration 

 occurs not only after the lens is removed from the eye but after it is 

 displaced so that direct continuity with the iris is lost and after lens de- 

 generation by X- radiation (Politzer). The fact that the origin of the re- 

 generated lens is different from its embryonic origin and the apparent 

 limitation of potency to the upper or dorsal part of the iris led Wolff to 

 a teleological interpretation which was opposed by Fischel, but many 

 investigators have concerned themselves chiefly or wholly with presenta- 

 tion of data. Sato (1930), transplanting pieces of the upper iris to another 

 eye, found a gradient of decreasing lens potency from the most dorsal iris 

 region. In further experiments he implanted optic primordia of different 

 embryonic stages with dorsiventral reversal, so that the originally dorsal 

 side of the optic cup was ventral; and at a later stage shortly before 

 metamorphosis, he removed the lens (Sato, 1933a, b). According to the 

 stage of dorsiventral reversal, the choroid fissure developed ventral in 

 position, dorsal in origin, or two fissures developed, or the original dorsi- 

 ventrality persisted. Apparently, dorsiventrality of the optic primordium 

 is not irreversibly fixed in earlier stages ; in later stages the original dorsi- 

 ventrality apparently determines one fissure, the imposed dorsiventrality 

 another; still later, the fissure develops in its normal position with respect 

 to the original dorsiventrality. The lens regenerates from the iris region 

 opposite the choroid fissure or, when two fissures are present, opposite 

 the more completely developed ; and a gradient of lens potency decreasing 

 from the iris region opposite the fissure is present. Sato concludes that the 

 choroid fissure exercises an inhibiting action on lens regeneration, so that 

 the lens arises from the iris region farthest from it. 



Sato's data, as well as those of others, suggest a more general inter- 

 pretation, that is, that both position of choroid fissure and region of lens 

 regeneration are expressions of dorsiventral pattern, evidently a dorsiven- 

 tral gradient, either the original gradient or that imposed on the im- 

 planted, dorsiventrally reversed eye. The high region of the dorsiventral 



" Colucci, 1891; Wolff, 1895, 1901, 1913; E. Miiller, 1896; Fischel, 1900a, 1902; Spemann, 

 1905; Wachs, 1914, 1920; Ogawa, 1921; Beckwith, 1927; Adelmann, 1928; Sato, 19330, b, 

 1935; Toro, 1932, Kesselyak, 1936; Politzer, 1936, Monroy, 1939. Lens regeneration from the 

 iris has been observed in adults of certain urodeles; but in Amblystoma punctatum and A. ti- 

 grinum and in the anurans Rana clamitans, R. pipiens, and R. sylvatica it does not occur even 

 in larval stages; in these forms, however, lens fragments implanted or remaining after lens 

 removal may regenerate lens (Stone and Sapir, 1940, "Experimental studies on the regenera- 

 tion of the lens," Jour. Exp. ZooL, 85). 



