No. 631] CONGENITAL PALSY IN GUINEA-PIGS 133 



offspring when two heterozygotes are mated, (2) the pro- 

 portion of homozygous to heterozygous individuals 

 among the normal offspring of such matings, and (3) the 

 ratio of homozygous to heterozygous offspring when 

 homozygote was mated to a heterozygote. 



Since for practical reasons the number of offspring 

 which can be produced from any particular pair of par- 

 ents is limited, it became necessary to set a definite arbi- 

 trary number which should be taken as the minimum to 

 indicate a fair probability that the animal being tested 

 was homozygous for normality if no recessive young 

 were born. Five was chosen as this minimum, but in 

 every instance larger numbers were obtained where pos- 

 sible. All cases in which less than five normal offspring 

 were obtained without the appearance of a recessive are 

 discarded from the calculations. Furthermore, only six 

 of the thirty individuals rated as homozygous normals on 

 the basis of their breeding behavior had so few as five off- 

 spring, and in most cases the number was considerably 

 larger, as is shown in Table I. 



TABLE I 



Animals Rated \s rioMozvcors Xokm w. a\o the Number of Exclusively 



