Warren Harmon Lewis 



507 



The operations were performed on the right side and the uninjured 

 left side used for comparison. All the figures were made with the aid 

 of a camera lucida. 



A. Will the Lens Arise from the Ectoderm without the Con- 

 tact OF the Optic Vesicle on the Skin? 



Series DF and IV. 



In the first series ° of experiments, series DF and IV, the optic vesicle 

 was removed at a stage before it had had any visible influence on the skin 

 leading to lens formation, and transplanted some distance caudally. The 

 experiments were performed on the emliryos of Eana palustris shortly 



Fig. 1. * Fig. 3. 



Fig. 1. Outline of stage IT. X 8 diameters. The dotted line ob, incision for skin flap, oo, 

 plane of section of Fig. 3. 



Fig. 3. Outline of section through the head of stage II in the plane, oo Fig. 1. ab, line 

 along which optic vesicle was cut away. X 41 diameters. 



after the closure of the medullary folds, see Figs. 1 and 2. An 

 incision was made along the line ah, see Fig. 1, and the anterior skin 

 flap carefully turned forward without tearing either it or the structures 

 beneath. It is quite easy at this stage, as the optic vesicle is not ad- 

 herent to the skin. At a later stage, however, the optic vesicle becomes 

 quite firmly adherent to the skin and can scarcely be separated from it 

 without tearing either one or the other, and consequently is unsuitable 

 for the operations of series DF or IV. After the skin flap is laid for- 

 ward and the small round optic vesicle exposed, the latter was cut off 

 close to its attachment to the brain, leaving a large opening into the brain 



° All the experiments of a series were done on embryos of an age as near 

 alike as possible and as near as possible in the same manner. A certain 

 amount of variation in the experiments of a series was unavoidable and 

 consequently the results vary somewhat. 



