EFFECTS OF GONAD GRAFTS IN CHICKS 



9 



and allantois. The graft lies in this mesoderm. The chorio- 

 allantoic membrane appears in general nearly normal in structure, 

 but is irregularly bounded and its cells somewhat more compact 

 than is normally the case. 



2. Vascular area. Within the membranes just described and 

 encircling the graft proper is a vascular layer. This consists 

 originally of a stroma of mesoderm cells richly infiltrated with 

 small blood-vessels, but with the growth of the graft the stroma 

 is greatly increased in quantity. It is composed of spindle- 

 shaped connective-tissue cells and of fibers; it is somewhat more 

 loose in structure than the normal stroma. Blood-vessels are 



Text fig. A Diagram of the structure of a growing graft (testis), ec, ecto- 

 derm of chorion; ea, entoderm of allantois; hv, blood-vessel; va, vascular area; 

 ga, growing area; sc, connective-tissue sheath; jia, necrotic area; tt, transitional 

 tubules, regenerating at one end and necrotic at the other. 



distributed abundantly through the stroma and show a tendency 

 to aggregate toward the center of the graft. Intermixed with 

 the stroma structure one finds numerous leucocytes, singl}^ or 

 in groups. Some of these are hemoblasts or lymphoblasts; 

 others are granuloblasts, granulocytes, or polymorphonuclear 

 leucocytes. Many of them contain granules which stain with 

 hemotoxylin and eosin; these are polymorphonuclear. Mitotic 

 figures are not uncommon. Of course this abnormal accumu- 

 lation of leucocytes around the graft is a response to the presence 

 of foreign tissue. 



3. Growing area of the graft. This is naturally the most 

 important region of the graft — the area occupied by the growing 

 tissues of the graft. In the case of testis graft one finds in this 



