No. 631] CONGENITAL PALSY IN GUINEA-PIGS 135 



reasons. In the first place, the palsied animals appear 

 as strong and vigorous when born, and in all respects ex- 

 cept for the nervous condition as fully developed as the 

 normal young. This is further borne out by the weights, 

 the weight of the palsied young being as great, indeed 

 averaging slightly more at birth than that of the normals. 

 The weights at birth of the living young from Nn X Nn 

 matings are shown in Table IV, from which it will be seen 



TABLE IV 



that 170 normal offspring averaged 88.65 grams, whereas 

 61 palsied young average 90.19 grams. The slightly 

 greater weight of the latter is probably not sigmiieant. 

 These facts seem to indicate strongly that the congenital 

 death rate was not differential with respect to palsy. 



2. Proportion of Homozygous to Heterozygous Individ- 

 uals among the Normal Offspring of NnXNn Matings. 

 —Further proof that we were dealing with a single factor 

 difference was provided by tests of the normal offspring 

 from matings of heterozygote to heterozygote. These 

 should, of course, consist of two heterozygous individuals 

 to each extracted homozygous dominant, which should 

 breed as free from the defect as any animals from non- 

 Palsy stock. As shown in the right-hand half of Table 

 HI, 22 of the 183 normal individuals were tested, of 

 which 7 proved to be NN and 15 Nn, the theoretical expec- 

 tations being 7.3 and 14.6, respectively. 



3. Ratio of Homozygous to Heterozygous Offspring 

 from Mating NNxNn.-One other type of test was 



