x] Certain Females normally Hybrid 193 



nevertheless, to imagine that the output of gametes repre- 

 senting respectively one or other of a pair of allelomorphs 

 may be influenced by circumstances. We have not yet any 

 proof that such a phenomenon may occur; but the long runs 

 of unexpected numbers which we from time to time witness 

 in the course of Mendelian experiments are suggestive of 

 some definite disturbance of the normal equality in the out- 

 put of the two kinds of gametes. Data for an adequate 

 statistical examination of this question scarcely exist as yet, 

 but if it be found that the long runs are too frequent to be 

 accepted at all readily as chance aberrations, the search for 

 environmental causes of disturbance will have to be under- 

 taken. 



The second conclusion that we have reached is one 

 which no previous experience of nature could have led us to 

 anticipate. Naturalists are so accustomed to considering the 

 males and females of a true-breeding strain as of identical 

 composition, except in so far as their sex is concerned, that 

 those who have no practical acquaintance with genetic 

 phenomena may find a difficulty in realizing that the females 

 of a breed can be hybrid in some important respect though 

 the males are not. The evidence however leaves no doubt 

 of the reality of this conclusion. The consequences of such 

 a discovery are not easy to foresee, but as in our very 

 limited range of experimental study three such cases have 

 already been encountered, we may feel fairly sure that this 



resemblance which such degenerating ova bore to those which Russo 

 regards as destined to become males. Consequently before that view of 

 their nature is adopted, the relation of the so-called " male " ova to the 

 degenerating ova will need very careful study ; for it seems as yet not 

 unlikely that those differences which Russo has taken to indicate maleness 

 may prove to be due to incipient degeneration. 



In addition to the detection of the distinction between male and 

 female ova Russo states that he has, by administration of lecithin, 

 succeeded in greatly increasing the proportion of female births. He 

 gives figures to show that in rabbits, normally bred, male births are largely 

 in excess of female births, and another series of figures showing a great 

 excess of female births from females treated with lecithin. Both lists of 

 figures are however declared to be selected from a larger number in order 

 to illustrate the author's thesis. It is to be hoped that the full lists will 

 soon be published. Meanwhile I may mention that Mr Hurst in his very 

 considerable experience of breeding rabbits under normal conditions has 

 found the male and female births to be sensibly equal in number. 



B. H. 13 



