EXPERIMENTS ON THE ORIGIN AND DIFFERENTIATION 
OF THE LENS IN AMBLYSTOMA. 
BY 
WILBUR L. LE CRON, 
Student of Medicine. 
Anatomical Laboratory, Johns Hopkins University. 
WitTH 5 PLATES. 
Spemann’ destroyed the rudiment of the optic vesicle on the wide 
open medullary plate of Rana fusca with a hot needle. When the eye 
failed to regenerate the lens was wanting, although the normal lens 
forming ectoderm had not been injured. 
Lewis * cut away the optic vesicle in Rana palustris at a later stage, 
shortly after the closure of the neural folds, but before there were any 
signs of lens formation. The normal lens forming ectoderm was unin- 
jured, but it failed to give origin to the lens, unless there was sufficient 
regeneration of the eye to bring it into contact with the ectoderm. 
Lewis also transplanted the optic vesicles so cut away, beneath the 
ectoderm in other regions of the head. In embryos where such trans- 
planted eyes came into contact with the overlying ectoderm, lens forma- 
tion often occurred. His method of operation consisted in making an 
incision caudal to the eye region, turning the skin flap forward and cut- 
ting away the exposed optic vesicle, and then replacing the skin flap into 
its original position. 
These experiments indicate very clearly that the lens is dependent for 
its origin upon the contact influence of the optic vesicle upon the ecto- 
derm ; the lens, in other words, is not a self-originating structure. 
The beginning then of lens formation, namely, the thickening of the 
inner layer of the ectoderm to form the lens-plate, is dependent upon 
some influence exerted on this ectoderm by the optic vesicle. Is the con- 
tinued differentiation of this lens-plate into the lens-bud, the lens-vesicle, 
and lastly the lens independent of any farther influence of the optic 
vesicle, or is the normal differentiation of the lens-plate dependent upon 
the continued influence of the optic vesicle and optic cup? 
At the suggestion of Dr. Lewis, I undertook in the spring of 1905 an 
1Ueber Correlationen in der Entwickelung des Auges. Verhandl. der Anat. 
Gesellschaft, 1901. 
2Hxperimental Studies on the Development of the Eye in Amphibia. I. 
On the Origin of the Lens. Rana palustris. Am. Jour. of Anat., III, 1904. 
AMERICAN JOURNAL OF ANATOMY.—VOL. VI. 
