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THE AMERICAN NATURALIST [Vol.XLIV 



elusively to female offspring. There are thus in rabbits two 

 kinds of eggs corresponding, respectively, to each sex: (1) well 

 nourished, highly anabolic, or female; (2) poorly nourished, 

 slightly anabolic (or katabolic) or male. 



The sperm, containing chemical substances similar to the eggs, 

 are regarded as merely giving aid in the development of a process 

 already begun in the egg leading towards the determination of a 

 particular sex. That the sperm has a complementary and not an 

 antagonistic role in sex-production seems established by the fact 

 that the percentage of female offspring is higher when both male 

 and female have been subjected to the lecithin treatment before 

 union. 



For the experiments Russo employed selected and ordinary 

 varieties of rabbits. His chief aim was to "fix" a particular 

 "unit character" of the female in the offspring (mostly female) 

 of the first hybrid generation. The character selected was the 

 color of the hair. Females of recent races characterized for hair 

 color, i. e. } white (albino, Himalaya, Angora, etc.), were crossed 

 with males of various phylogenetically older races (e. g., 

 "Grigia" — gray, and "Nero" — black). The best results were 

 obtained from crosses between Himalaya females and "Nero" 

 males. On crossing females of either albino or Himalaya races 

 with males of "Grigia" and "Nero" stocks the offspring of the 

 first generation always had the color of the male, i. e. f gray or 

 black, respectively, showing that these crosses ordinarily conform 

 to the Mendelian law of dominance. Moreover, Russo notes that 

 in nature the number of male offspring always exceeds that of 

 the female, the percentage of the former being variously given 

 as from 52 to 58 per cent. 



When the same females were subjected to the lecithin treat- 

 ment before conception, the offspring of crosses similar to the 

 above were in the first generation preponderatingly of the type 

 of the newer or female race. There frequently appeared atavis- 

 tic exceptions, interpreted as due to a late ripening of the eggs 

 concerned which consequently remained unaffected by the 

 lecithin. 



The most clear-cut result was obtained from the following 

 experiment: A preliminary experiment, several times repeated, 

 having shown that the ordinary cross conformed to the law of 

 dominance, a young well-nourished "Polacca" (white) lecithin- 

 treated female was crossed with a "Nero" male (black). The 

 resulting progeny included 6 females (5 white) and 2 males (1 



