GENETIC STUDIES OF RABBITS AND RATS. 



29 



parts of the body, or whether factors, independent one of another, 

 govern size in different parts of the body. The conclusion is reached 

 that the genetic agencies affecting size in rabbits are general in their 

 action, influencing in the same general direction all parts of the body. 

 The same would probably be found true for man and other mammals, 

 perhaps for vertebrates in general, but not for plants in which hor- 

 mone action is less in evidence. 



8. No linkage relation has been found to exist between size and 

 any simple (unifactorial) Mendelian character, such as albinism, 

 yellow coat-color, dilution, or angora coat. This result is in har- 

 mony with the view that unifactorial characters have their genes 

 located each in a single chromosome, while size is influenced by genes 

 located in many or all chromosomes. 



9. In rabbits, size differences correlated with sex are very slight. 

 In skeletal dimensions the adult male averages larger by 1 or 2 per 

 cent, but in weight females surpass males, particularly in the larger 

 breeds of rabbits; yet the differences are so small as not to disturb 

 appreciably the correlation coefficients based on data in which both 

 sexes are included. In ear-length no significant difference between 

 the sexes can be detected. 



TABLES. 



Table 1. — Average weight in grama of rabbits oj the several groups studied, at various ages. 

 Data used in the construction of figure 3. 



Group. 



No. 



Age in days. 



30 



40 60 90 120 160 180 210 240 270 300 330 360 



Polish 



Himalayan 

 Flemish . . . 

 Fi, PXH.. 

 Fi, PXF. . 

 F,. PXH.. 



308 



605 

 363 

 377 

 350 



414 

 422 

 870 

 459 

 478 

 521 



549 

 574 

 1172 

 661 

 683 

 769 



779 

 824 

 1800 

 1002 

 1210 

 1227 



973 

 1049 

 2260 

 1307 

 1641 

 1802 



1133 

 1240 

 2630 

 1580 

 1988 

 2154 



1244 

 1423 

 2820 

 1752 

 2166 

 2386 



1284 

 1536 

 2940 

 1854 

 2283 

 2553 



1297 

 1659 



1311 

 1705 



1328 

 1753 



1344 

 1800 



1898 

 2388 

 2680 



1927 

 2443 

 2719 



1952 

 2466 

 2752 



1962 

 2485 

 2789 



1359 

 1806 

 3240 

 1971 

 2507 

 2826 



Table 2. — Comparative weights in grams of the two sexes in the groups of rabbits studied. 



