LEIGH HOADLEY. 



within this membrane was so complete that no injury was done 

 to these parts when the membrane containing the graft was 

 removed from the shell of the host. 



Very little tissue save those already mentioned occurs in this 

 graft. The sclerotic coat of the eye is present throughout. To 

 one side there is a small mass of brain tissue containing typical 

 nerve cells and processes. This is heavily infiltrated with blood 

 vessels and not easily identified. Adjacent to this region, the 

 tapetum and retina are very much convoluted and disorganized, 

 and a heavy infiltration of blood corpuscles among the folds 

 makes the identification of definite structures impossible. The 

 optic nerve and pecten which would be located in this area under 

 normal conditions cannot be found. The disorganization and 

 the infiltration of the blood cells may mask their position as 

 degenerative changes are apparent. The entire graft is sur- 

 rounded by the mesenchymatous tissue of the host. 



In not all of the grafts is brain tissue present. A graft of the 

 optic region of a thirty-five hour chick, case 14 A I , when sectioned 

 shows a very evenly shaped posterior chamber lined by well dif- 

 ferentiated retina. This eye shows the same differentiation of 

 retina and tapetum as graft 9 A I above, though there is a total 

 absence of brain and cartilage tissue. The various layers of the 

 retina are well defined. The cut edges of the excised optic vesicle 

 have drawn together and the point at which they have fused is 

 marked by a thickening and by slight convolutions of both tape- 

 tum and retina. No lens tissue is present in the sections, prob- 

 ably due to the failure of its primordium to be incorporated. The 

 grafted tissue is surrounded by an extremely thin layer of host 

 mesenchyme. In no place is there any sign of brain tissue, optic 

 nerve, or pecten, though the point at which they would normally 

 occur is definable. 



Graft 19 E .13 from a forty-eight hour chick embryo, is some- 

 what similar to 9 A I above. This case, after seven days of 

 growth, a total of nine days, showed a graft 4 mm. x 4 mm. in 

 size. A drawing of this graft as it appeared in alcohol before 

 sectioning is shown in Fig. I. The heavy'pigrnentation o f the 

 greater portion of the surface will be noted, together with the 

 absence of pigment from a portion of the tipper face. It w.i- 



