CHORIO-ALLANTOIC GRAFTS. 



307 



differentiation is very striking. The two nuclear layers are 

 present and separated by the inner fiber layer which contains the 

 nuclei in definite strands. In tangential sections this layer also 

 show- many fiber tracts. In this case, this fiber layer also shows 

 a very heavy infiltration of Mood vessels, a condition not present 

 in the normal. Such a condition seem- to be correlated with 



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i-ertain oilier dil'tereiu r- in the dc\ elMjunent of the parts of the 

 primordium. the mo-i evident of \\ hich is in the outer fiber layer. 

 In thi- i^raft (Fig. [0 . t he outer fiber layer is not bounded by an 

 external limiting membrane and as a result the libers penetrate 

 the adjacent me-i-nch\ me. The-. -til.. rown out into the 



meseiu^hyme, or the me-eiich\ niatoii- ti ue of the host has 

 advanced into the nervou- ti--ur of the i;raft ; the width of tin- 

 zone in which libers alone are prc-ent i- very variable. The 

 outer layer may even be lacking in many place-, the outer nuclear 

 layer bi-in^ in immediate contact with the loose mesenchyme 

 21 



