242 E. I. WERBER. 



of Wachs in which a fragment of the eye cup containing both iris 

 and retina (cf. Fig. 50) transplanted "dicht unter die Haut" 

 has failed to stimulate lens-formation from the latter, but instead 

 has so altered it that it gave the appearance "einer kleinen 

 Cornea." For in these cases the failure to induce the lentogenic 

 reaction might have to be attributed to the retinal as well to the 

 iris-part of the transplanted fragment ; it may, however, be due to 

 the circumstance that the skin of the relatively old larvae was no 

 longer capable of responding to a "lentogenic stimulus." The 

 latter possibility may be implied from the (above-mentioned) case 

 (pp. 237 and 241) in which owing to the operation an ingrowing 

 strand of epithelium formed a lens under the influence of the 

 transplanted fragment of the optic cup. For, as Wachs himself 

 concludes, we are in that case (No. 39) dealing with "Abkomm- 

 linge von Hautzellen, die, neugebildet und noch undifferenziert, 

 offenbar die gleiche Fahigkeit der Linsenfaserbildung haben 

 konnen, wie einst die junge Haut . . . :> (/. c., p. 430). 



But while there is, as we see, no definitely known instance of 

 lens-formation owing to a stimulus from the iris, there is, on the 

 other hand, nothing that would contradict the assumption that 

 the iris is capable of exerting such a stimulus on ectodermal 

 derivatives. Moreover, the very fact that the other parts of the 

 optic cup (retina and tapetum nigrum) can furnish the lento- 

 genic stimulus would make it appear very probable that the iris 

 which genetically is also a part of the optic cup (proper), is like- 

 wise possessed of the ability to induce the "lentogenic reaction." 



Granting the correctness of this assumption (which eventually 

 may be borne out by suitable experiments) , we would in the case 

 of the iris be confronted by the same conditions as in the case of 

 the retina. It is known that the iris can form a lens, and if, as 

 seems probable, it can also induce the formation of a lens from 

 ectodermal epithelium, the assumption may be justified that in 

 the formation of a lens from the pupillary edge of the iris, which 

 is an ectodermal derivative, its 'cells respond to their own "len- 

 togenic enzyme." 



These conditions apparently obtaining in the formation of 

 lentoids from the retina and very probably also in the "regenera- 

 tion" (secondary formation) of the lens from the iris are in prin- 



