ORIGIN OF 'independent' LENSES 359 



relation between optic cup and lens can now, in the light of our 

 findings, be fully harmonized with it. 



Of the 'independent' lenses recorded in the experiments of 

 other authors, those described by King (I.e.) can easily be ac- 

 counted for, when it is considered that the method employed in 

 her experiments contains an uncontrollable source of error. For 

 it is easy to see that of the optic vesicles of frog larvae which 

 she destroyed, some particles might have been dispersed and come 

 into permanent contact with the overlying epidermis in which in 

 this manner the 'lentogenic reaction' was induced. Provided 

 that this conclusion is correct (and I think it is highly probable 

 that it is) it is on the other hand just as easy to understand why 

 for the same frog species in the experiments of Lewis (I.e.) in 

 whicli a more reliable method was employed, the recorded results 

 were the opposite to those of King's. By skillful operations, 

 Lewis removed the optic vesicle in such a manner that no frag- 

 ments of it came into contact with overlying ectoderm. There- 

 fore the 'lentogenic reaction' was never induced in the latter on 

 the side operated upon. The same would seem to hold good for 

 the experiments on Amblystoma performed by Le Cron (I.e.) 

 under Lewis' direction. It fellows from these considerations 

 that the free lens buds recorded by King are in their origin 

 similar to those of blastolytic origin in teratophthalmic embryos, 

 the dissociation or dispersion of optic vesicle substance (histoly- 

 sis) having been induced by mechanical force. 



Greater difficulty is presented to our interpretr.tion by the 

 contradicting results which Spemann ('12) has obtained in two 

 frog species of the same genus. However, this difficulty is not- 

 insurmountable, for I am firmly convinced that the apparent 

 discrepancies in the effect of the same operations in species of 

 the same genus are not due to primary differences in morpho- 

 genetic potentiality, but rr.ther to some secondary factor, which, 

 however, in these minutely delicate operations becomes of great 

 importance inasmuch as it may present a source of unavoidable 

 error similar to that which I have assumed as present in King's 

 experiments. Spemann ('12) himself has pointed out some tech- 

 nical difficulties which may affect the accuracy of experimenta- 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL 21, NO 3 



