8 



BULLETIN 1121, U. S. DEPARTMENT OP AGEICULTUEE. 





ing. The records in four previous years, 1911-1915, as well as in 

 these years show that the total inbred stock rose and fell in 



close parallelism with 



the control stock. 



2.SO I I I I I I I I I I I I I / |\ I The rising records for 



the years 1916-1919 

 certainly give no evi- 

 dence of continued 

 genetic decline. It 

 would have been de- 

 sirable to have used 

 only one family as a 

 criterion of the rise 

 — ~^i?s — 7S7^ — 73^5 — 7373 and tall m envn-on- 



FiQ. 5.— The average size of Utters produced by the inbred stock in mental Conditions if 

 successive 3-nionth periods, 1916-1919. Sufficient numb CrS 



had been available. As it was, it seemed best to use the total 

 inbred stock. This stock was largely composed of five families 

 which were kept up to about the same proportional represen- 

 tation during this 

 period. The com- 

 bined averages for 

 the other families, 

 moreover, were close 

 in most respects to 

 the average of these 

 five important fami- 

 lies. 



A comparison of 

 the entries in Table 



28 with the corre- 

 sponding ones in Table 



29 brings out, it is be- 

 lieved, the superiority 

 or inferiority of each 

 experiment to the 

 total inbred stock, 

 free from the influ- 

 ence of seasonal fluctuations and of size of litter on the other char- 

 acters. 



/ 



o \ 1 1 1 1 1 1 1 1 1 1 I I I i 



/9/G /a/T" /9/a /9/a 



Fig. 6. — The average number of young raised per year, by mature mat- 

 ings, inbred stock, during successive 3-month periods, 1916-1919. 



