EXPERIMENTAL STUDIES ON THE DEVELOPMENT OF THE 

 EYE IN AMPHIBIA. 



I. On the Origin of the Lens. Rana palustris. 



BY 



WARREN HARMON LEWIS, M. D. 



From the Anatomical Laboratory of Johns Hopkins University. 



""sT^iTH 42 Text Figures. 



This article is intended as a contribution to the study of correlative 

 emhryology, i. e., the influence of intra-organic environment in develop- 

 ment. Our problem is to determine how far the various organs and 

 tissues of an organism are dependent or independent of the various other 

 organs. and tissues for their origin, differentiation and growth. An 

 organ may be dependent or independent (self differentiating) of other 

 organs for its initial origin, or for its subsequent development, or it 

 may be d'ependent on a series of influences for its proper development. 



It will be natural to inquire into the nature of these influences to de- 

 termine if they are mechanical, chemical, electrical or unknown influ- 

 ences still to be discovered. 



In the present paper I shall show : 



A. That the lens does not arise from the ectoderm without the con- 

 tact influence of the optic vesicle. 



B. That the optic vesicle can stimulate a lens to form from various 

 portions of the ectoderm and even from ectoderm from the abdomen 

 of another species of frog, indicating thereby that there is no especial 

 predetermined urea of the ectoderm, which must be stimulated in order 

 that a lens may arise. 



C. That various portions of the optic vesicle have the power of stimu- 

 lating lens-formation. 



Spemann ' has shown indirectly that the lens is dependent on the influ- 

 ence of the optic vesicle for its origin from the epithelium of the skin. 

 He employed the method of destroying partially or entirely the rudi- 



lUeber Correlationen in der Entwickelung des Auges. Verhandl. der 

 Anat. Gesell., 1901. 



American .Tournal of Anatomy. — Vol. III. 

 36 



