236 E. I. WERBER. 



might easily lead to the conclusion that the "eyeless" lenses 

 arose by self-differentiation of the ectoderm. But careful obser- 

 vation and rigid analysis of the noted relations of parts to each 

 other leaves no doubt that all these lenses are products of stimuli 

 from dispersed optic-cup substance. 



In a Fundulns monster described by me in a former paper 

 (Werber 'i6r) there were no eye defects, but owing to a special 

 method optic-cup substance was very profusely dissociated and 

 dispersed through a large part of the head. Owing to this con- 

 dition a great deal of the head ectoderm and even the epithelium 

 of the mouth, infected, as it were, with such fragments of the 

 optic anlage, responded by the formation of a great number of 

 lentoids. Many more monsters resulting from the employment 

 of the same method were examined in sections and they show 

 very similar conditions. In other experiments in which the 

 method employed was more destructive various eye defects such 

 as monophthalmia or synophthalmia or anophthalmia resulted. 

 On examination of sections through these embryos not only 

 lentoids, but well-differentiated, "eyeless" lenses were frequently 

 observed and in nearly every one of these cases some more or less 

 obvious traces of optic-cup substance can be observed in their 

 immediate neighborhood. 



In the same paper I have pointed out that the "independ- 

 ent" lenses which Stockard ('09, '10) described in teratoph- 

 thalmic Fundulus embryos have also undoubtedly resulted from 

 contact of ectoderm with such blastolytic fragments of the eye 

 anlage. 



On that occasion I have also called attention to a very prob- 

 able source of error in King's ( '05) l experiments in view of which 

 the evidence she brought forth for the independent development 

 of the lens in Rana palustris in contradiction to Lewis's ('04) 

 unmistakable evidence to the contrary, appears to be illusory. 



Experiments of other observers (Bell '06 and '07 and Ekman 

 '14) also yielded results which decidedly contradict the idea of 

 the independent development of the lens. And a very beautiful 

 demonstration of the "lentogenic reaction" of the epidermis to a 

 stimulus from an eye fragment was recently furnished by Wachs 

 ('14, p. 430 and Figs. 46, 47, 48 and 49). 



1 Cf. the footnote on p. 221 of this paper. 



