Intersexual females start their development as females and then at a certain point in development change their differentiation and finish as males, and since the hard parts of an insect are external and composed of chitin any of them that have hardened before the switch-over remain unaltered by it. From an examination of the parts which are sexually dimorphic, it is possible to decide in the case of any particular individual exactly when the change over took place. These intersexes are sex-mosaics in time.
From these facts Goldschmidt deduced the following con clusions: (r) Each sex possesses the potentialities of the other since either can become intersexual.
(2) The type of sexual differentiation that the fertilised egg will pursue is determined at the time of, and by the mechanism of, fertilisation. If the constituents of intersexuality are in the fertilised egg, then the individual will inevitably become an inter sexual form.
(3) The normal determination of sex is bound up with the X : 2X mechanism. But as this does not prevent the occurrence of intersexuality and sex-reversal, it cannot be the mere presence of these chromosomes or the factors contained within them that counts, but rather their quantitative effect during development.
(4) The mode of inheritance of this intersexuality shows that since the female in Lymantria is XY, and since her single X chromosome is received from her father, the male-determining factors in sex-determination are transmitted in the X-chromo some.
(5) Other factors concerned in sex-determination in Lymantria are purely maternal in inheritance, being resident in the Y chromosome. A daughter receives her Y-chromosome from her mother. But since a male has no Y-chromosome, the factors in the Y-chromosome must have exerted their action on the unripe egg when this contained both X- and Y-chromosomes. If all eggs are to be alike in respect of the V-borne genes, these must have acted and their products must have specifically affected the cytoplasm before the X and Y became disjoined.
(6) The fact that the females of similar constitution give dif ferent results when mated with males of dissimilar constitution shows that the sex-determining genes in the X-chromosome differ quantitatively in the different races. The fact that males of similar constitution give different results when mated with females of dissimilar constitution shows also that the sex-determining factors resident in the Y-chromosome can be different quanti tatively.
It will be seen that if both X-borne and V-borne sex-determining genes can so vary quantitatively among themselves, an infinite variety of different combinations can be made, deliberately or by chance.
Goldschmidt infers with reason that the sexual characterisation of any particular organ of the sex-equipment depends on whether one or the other type of sex-differentiating substance is effectively in excess at the time when the organ arises in development. He interprets the mosaic character of the intersex on the assumption that the amount of sex-differentiating substances produced in virtue of the presence of the corresponding sex-determining fac tors is not constant throughout life : that at one time the male differentiating substance is in excess, at another the female. In the male of the moth M > F and the male-differentiating substance is effectively in excess until the period of development is com plete. In the female M
A male of a race whose sex-determining genes work at a faster rate is crossed with a female of a race in which these factors work slower. The female-determining factor F is always inherited through the mother and in all the offspring there will be this factor F and the female-differentiating substance will be pro duced in all at the same rate. But the male offspring will receive one M from their mother, and the other, the quick-acting M, from their father, so that in a given time the male-differentiating substance will be effectively in excess during development. The female offspring will have only the paternal M, and therefore the amount of male-differentiating substance will increase relatively to the amount of the female-differentiating substance, overtake it, and finally supplant it, and from this point onwards any sex characters which still have to develop will be male. The indi vidual will be a female intersex. It is not the absolute but the relative rates of production of male- and female-differentiating substances that control the modelling of the sex-equipment. Sex-reversal in these cases is due to genetic causes—the fertilised egg contains inevitably within itself the seed of its eventual transformation in the form of a quantitative disharmony of the sex-determining factors.