6664 o n <>32 12 2f 



32 



Fig. 31. Descent of a form of stationary night-blindness. (Condensed from tl 

 Only those families which contain affected members are here set out in detai 

 by the i6 th black symbol from the left in generation vn. 



Black symbols show the night-blind individuals. The descent is alwa 

 According to the records there is a great excess of normals over the affected 

 theless the table gives a remarkable illustration of the permanence and mode 



