TACTICS IN PIGMENT-CELL RESEARCH 343 



regions. The only types known to have restricted pigment areas are those carrying E 

 in their genotypes; then only the extremities (wing tips, ventral regions, and feet) are 

 white in the newly hatched chick. Even when migration of pigment cells appears to 

 be retarded by teratogenic agents until only a small pigmented area remains on the 

 back in the down pattern of £ types, the birds eventually become fully pigmented. 747 



