238 E. I. WERBER. 



layers of the eye cup. For evidence is not lacking that the tape- 

 turn nigrum is also capable of inducing the development of a lens 

 (or lentoid) when in contact with ectodermal epithelium. Thus, 

 as pointed out above (p. 235), some of the "independent" 

 lenses recorded by Mencl ( '08) very clearly owe their origin to 

 contact of ectoderm with tapetum nigrum fragments (" Pig- 

 men tblaschen," "Pigmentanhaufungen." " Pigmentmasse"). 

 It was also mentioned that in a considerable number of Fundidus 

 monsters in my possession "independent" lenses and lentoids 

 can be demonstrated to be due to this "enzyme action" of the 

 tapetum nigrum. This ability of the pigment layer of the optic 

 cup is also suggested by some of Spemann's ('12) and Stockard's 

 (/. c.) figures. 



Whatever the nature of this action may be, whether or not 

 we agree to regard it as an enzyme action, as I am inclined to do> 

 it seems evident that all layers of the optic cup are capable of 

 it. Even the iris epithelium which genetically is also a part of 

 the optic cup may also be capable of this action. 



3. THE ORIGIN OF THE SECONDARY LENS- IN "REGENERATION." 1 



Bearing in mind this apparent ability of the embryonic ecto- 

 derm for lens formation by "enzyme action," it may perhaps 

 no longer be difficult to account, at least theoretically, for its 

 secondary formation "regeneration" from the iris after the 

 exstirpation of the primary lens from the fully developed eye 

 of the amphibian larva or even the adult. 



An attempt in this direction has already been made by Wachs 

 (/. c.} who accounts for this phenomenon as a reaction of the 

 epithelium of the iris to the "secretion" of the retina. Although 

 I find it difficult to accept the evidence for this secretion, I believe 

 that Wachs 's idea is correct in the main. The secondary for- 



1 1 am not inclined to regard the formation of the lens from the epithelium of the 

 iris as a case of true regeneration in the precise meaning of that term. From the 

 histogenetic point of mew we must say that this matrix (the iris} gives rise to the lens 

 for the first time and thus it generates, but does not regenerate, it. Considering, on 

 the other hand, the secondary lens in relation to the whole visual organ or to the entire 

 body of the animal, it is difficult to deny that we are here dialing with a case of what 

 is commonly regarded as regeneration ("Ersatz", " Nachbildung ", " Nach- 

 wachsen", " Wiederwachstum "). Without wishing, therefore, to decide pn the 

 fitness of the term in this connection, I am employing it only in quotation marks. 



