No. 530] CONCEPTION OF PURE LINES 73 



characters are carried by all cells alike ; possibly they go 

 along with the male-group, but this is not essential. 

 Whether they develop, or not, will depend on the pres- 

 ence of other genes in the cells. Thus when the Fmfm 

 group is present they will be suppressed, or when, as on 

 the other formulae, the FmFm group is present. We can 

 understand on this view why in the insects the male sec- 

 ondary sexual organs do not develop in the female after 

 removal of the ovaries, because in this group it is not 

 material derived from this source, but from materials 

 produced in the cells themselves, that bring about the 

 suppression. 



It has been demonstrated by Geoffroy Smith that 

 when the young males of the spider crab, luarclius mau- 

 retanicus, are infested by Sacculina the secondary sex- 

 ual characters of the female develop. It appears that 

 the parasite produces some substance that inhibits the 

 activity of the male-producing group in each cell, or 

 counteracts some materials produced there, so that the 

 female characters now find the situation favorable for 

 their development. When the young female crab is in- 

 fected by Sacculina she does not develop the male sec- 

 ondary characters, which is in harmony with the view 

 just stated for the manner of action of the parasite. 



In birds and in mammals it has long been recognized 

 that some substance is produced in the ovary that in- 

 hibits the development in the female of the male second- 

 ary sexual characters, for, after removal of the ovaries 

 the male characters may to some extent develop. It 

 seems fairly clear that here the female group in each 

 cell fails to entirely suppress the male characters; the 

 inhibiting effect from this source must be reinforced 

 from something produced in the ovary. Whether after 

 castration of the male the secondary sexual characters 

 of the female develop is not so clear, since some at least 

 of the characters that characterize the castrated male 

 may be juvenile. But on my view the possibility exists 

 for the castrated male to produce the secondary sexual 



