J. W. H. Harrison 13 



tilisation would generate zygotes of composition XX or XO, the former 

 assuredly males and the latter, if viable, also males. Nor is there 

 anything to prevent their being viable, for zygotes, proved cytologically 

 to be provided with an X chromosome alone, have been encountered in 

 Bridges' Drosophila cultures, and these were abnormal only in their 

 sterility. 



The difficulty, however, in both of these explanations seems to lie, 

 and more especially under the supposition that over-ripeness explains 

 the anomaly, in the fact that at first sight they offer nothing to account 

 for the intersexes. Nevertheless, over-ripeness may lead to diminished 

 vigour and vitality of the ova and a concomitant loss in power of the 

 sex genes which, in organisms with heterozygous females, would more 

 particularly affect that sex toward indifference and possibly inter- 

 sexuality. 



Under the second supposition there is also a feasible possibility, 

 and that is that the force urging the sex chromosomes to be included 

 in the polar body may be inadequate to force it far enough away in the 

 anaphase ; in which case it may be that a mechanical entanglement 

 occurs, trapping the Y chromosome between the egg nucleus and that 

 of the polar body, ending in the inclusion of part of it in the ovum and 

 part in the polar body — to me a very unlikely event. If such did 

 happen, the egg would be deficient in sex chromatin of the Y nature. 

 Consequently, the zygote proceeding from it would be unable to set up 

 in its entirety the system required to induce femaleness and a half- or 

 intersex appears. 



To conclude, whilst the last two theories offer some explanation, my 

 preferences lie, as stated, toward the potency theory, especially that 

 phase of it which represents sex as a matter of varying potential. 



If this be the case, then an easy extension enables one to explain 

 the curious sex results in Shull's Lychnis dioica families and in Correns' 

 hybrids between Bryonia alba and Bryonia dioica, whilst a parallel 

 theory has been evolved already independently by Goldschmidt to 

 account for the results in Brake's mongrels between Lymantria dispar 

 and its Japanese local race var. japonica. 



Inbreeding and its Effects in inducing the Appearance of Females in 

 Broods which, according to expectation, shoidd have been Unisexual 

 and Male. 



Owing to the great difficulties entailed in obtaining frequent 

 supplies of either Poecilopsis pomonaria or P. lapponaria, I have 



