COAT-COLOR IX HYBRIDS OF PEROMYSCUS EREMICUS. 49 



In connection with certain bone measurements, the authors 

 showed that a higher degree of bilateral asymmetry occurred in the 

 I generation of subspecific hybrids than in the F! generation. 1 

 \Ve have accordingly compared the two hybrid generations of this 

 cross in respect to asymmetry in the pigmentation of the feet. 

 The number < - in which the right and left feet were assigned 



to different grades was, however, very small. Four such cases 

 occurred ruin .ML; the 197 F l individuals and five among the 147 F 2 

 individuals. The larger proportion among the latter cannot be 

 .rdt-d a Meant. 2 



The f'illn\\ -:ng coefficients were computed, expressing the de- 

 gree o Int ion between parents and offspring in respect to 

 foot ] 'at ion : 



us F 4- .097 



J-'ratt-rcultU F -+- .159 



F ~ F + -34- 



F mothers F 4- .27* 



12 /0 



low degree of correlation between the pure race parents 



and their F, offspring (mean -.128) is believed to be due to the 



wide- ran^e in the age of the parent stock, in comparison with the 



hybrid animals, which were almost homogenous in this respect. 



Independent data have shown us that young animals have darker 



. and that the depth of pigmentation decreases with age, at 



: up to a certain point. Variability due to this cause would of 



coir .ken correlation. 



I-'ratt-nial correlations for this character are .358 .043 and 

 .198 ^4. for the FI and F 2 generations respectively. The dif- 



ference here is only 2.3 times its probable error. 



V. INTRA-RACIAL CORRELATIONS. 



\ i-ousiderable number of coefficients of correlation have been 



I Billed in order to ascertain to what degree certain characters 



tend to vary together among the individuals of a single race. 



Most of these need not concern us in the present paper. Some 



of them are of little biological interest, and some, indeed, express 



1 (," Si t., 1921. 



2 Tin- e results in the present case may well be due to the relative 

 crudity of t employed. The deviations from symmetry reconk-il f<>r the 

 paired l>"ii< - v < re only detected by exact measurements. 



