Experimental Studies on the Development of the Eye. 433 



cornea is formed it will disappear almost completely if the optic 

 cup and lens are entirely removed, without injury to the over- 

 lying cornea. 



The experiments in this paper with the sole exception of MD4 

 have been selected each from a series of several similar ones. 



METHODS. 



Embryos of various ages were operated upon under the binocu- 

 lar microscope. Either ordinary tap water or a 0.2 per cent 

 salt solution was used. The older embryos were first anes- 

 thetized with acetone-chloroform. The embryos were held with 

 a pair of fine forceps, and the incisions were made with a very 

 small pair of scissors, the points of which were ground with great 

 care. Ordinary needles complete the instruments needed. The 

 manipulation requires considerable practice, but one soon finds 

 experiments possible, which at the beginning seemed beyond such 

 methods. The method possesses great advantages over the use 

 of the hot needle or electric cautery. A new and very wide field 

 of work is opened by means of this dissection method and it will 

 undoubtedly throw much light upon developmental processes. 



The embryos were killed in Zenker's fluid, cut into serial sec- 

 tions. 5 /i or 10 /( in thickness and stained in hematoxylin and 

 Congo red. 



The operations were all performed on the right side. The 

 figures are all from photo-micrographs of transverse sections 

 through the region of the right eye. 



EXPERIMENTS. 



A. N on-development of the Cornea after Total Extirpation of 



the Eye. 



The numerous experiments on Rana palustris where the optic 

 vesicle was completely removed at an early stage before lens for- 

 mation and consequently long before there are any indications 

 of corneal formation, have all failed to show corneal changes in 

 the ectoderm which under normal conditions would have formed 

 corneas. Even days after the operation and long after the cornea 

 on the normal side of the head was well developed all traces of 



