232 E. I. WERBER. 



served in five cases. In thirteen of the embryos which had no 

 anterior lens Spemann accounts for its lack by the ingrowth of 

 mesenchyme into the space between the optic-vesicle fragment 

 and the epidermis, widened by the expansive growth of the otic 

 capsule which, owing to the transplantation came to occupy this 

 anterior position. He is unable, however, to suggest an expla- 

 nation for the lack of this lens in two cases, "wo kein Grund fiir 

 ihr Ausbleiben zu erkennen ist" (p. 73). 



From these experiments Spemann ('12, p. 77) concludes that 

 the optic vesicle of Bombinator is capable of exerting a specific 

 stimulus not only on the lens-forming cells, but also on other 

 parts of the head epidermis. 



This conclusion is, I think, only partly correct, the assumption 

 of "primare Linsenbildungszellen " being both unwarranted and 

 unnecessary. For leaving out of consideration the two cases 

 (which I should not wish to pre-judge), where no anterior lens 

 was formed while it should have been expected, we can conclude 

 only that its presence in the several other cases was due to the 

 specific stimulus from the anterior eye fragment. 



Briefly, the results of this series of experiments also contradict 

 Spemann 's opinion of the intermediate position of Bombinator 

 between Rana fusca and R. esculenta with regard to the ability 

 of independent differentiation of the lens. 



In all of Spemann' s work I find only a confirmation of his initial 

 results and strong support for the generalizations which he made in 

 IQOI and 1903, but no counter-evidence whatsoever that would 

 justify his present ('12) opinion. 



Other evidence for the independent development of the lens 

 brought forth by Mencl ('03, '08), King ('05) and Stockard ('10) 

 is no less illusory. 



Mencl ('03) described the head of an anophthalmic component 

 of an anadidymus in Salmo solar which possessed two laterally 

 'oca ted lenses although there could be observed "keine Spuren 

 von Augenblasen, ja nicht einmal von Anlagen derselben." 

 Both of these lenses were in close apposition to the deformed 

 brain, the larger one even having, owing to its growth, formed a 

 pit in the latter by pressure. Both "enses, however, were so 

 situated that their derivation from lateral parts of the head 



