E. I. WERBER. 



this manner. In all of them the anterior eye fragment lacks the 

 lens, while the posterior one in five embryos stimulated the for- 

 mation of a lens which " kann so vollkommen entwickelt sein 

 wie die normale" (p. 67). In one of these embryos the posterior 

 eye fragment possesses even two lenses which Spemann is in- 

 clined to regard as being due to mechanical separation of the 

 " Linsenmaterial " into two parts, although it would seem more 

 probable that the duplication of the lens in this case may (owing 

 to the operation) be due to mechanical histolysis of the eye frag- 

 ment which thus came into contact with the overlying epidermis 

 in two places. 



From these observations Spemann (p. 67) concludes that "die 

 w T eitgehende Determination der primaren Linsenbildungszellen 

 von Rana esculenta, welche sie zu selbststandiger Entw T icklung 

 befahigt, bringt es wohl mit sich, dass die iibrigen Epithelzellen, 

 auch die der nachsten Umgebung, nicht mehr imstande sind, 

 auf einen Reiz des Augenbechers mit Linsenbildung zu ant- 

 worten." 



These conclusions cannot be considered as warrantable. 

 Moreover, the results permit of an interpretation which, I believe, 

 is founded upon a much greater probability. It must be re- 

 membered that at the stage of development at which the opera- 

 tions were performed, it is only the tip ("die Kuppe") of the 

 eye vesicle that is protruding from the head. If that protruding 

 part be removed, the epidermis transplanted over the resulting 

 gap may, owing to the latter, fail to come into contact w r ith the 

 deeper part of the eye even on subsequent growth of the latter 

 owing to the obstruction formed by mesenchyme cells which may 

 grow into the gap before such contact can be effected. Spe- 

 mann 's Fig. 676 very forcibly suggests just this possibility. On 

 examining the anterior eye fragment of this figure one can observe 

 that it is not in contact with the epidermis. More significant, 

 however, is the observation in its lumen of a blood vessel and of 

 some mesenchyme cells which also fill the space between it and 

 the epidermis. 



Our interpretation of these apparently vexing cases receives 

 further support from the very fact that in the (a) series of these 

 experiments where the "Kuppe" of the optic vesicle had not 



