Another, perhaps better, suggestion is that the somatic characters of both sexes are present in each. Then as each somatic cell is descended without segregation from the fertilised ovum, we may suppose that the presence of the sex-chromosomes in the somatic cells themselves in some way determines whether male or female characters shall develop, without the aid of any hormones from the gonads. This theory would be quite compatible with the belief that adaptive somatic sex-characters may be due to external stimulation, for supposing that the hypertrophy or modification is conveyed to the determinants in the gametocytes, and was confined to one sex, _e.g._ the male, then these determinants would be modified in association with the sex-chromosomes of that sex, and thus though after reduction and fertilisation they would be present in the female zygote also, they would not develop in that sex. Thus supposing _M_ to represent a modification acquired in the male and _m_ the absence of the modification, such as the feathered antenna of a moth, and the sex-chromosomes to be _X_ and _Y_, then we should have in the gametocytes-- Male Female _MM mm_ _XX XY_ Gametes _MX, MX: mXmY_ Zygotes _MmXX male, MmXY female_, and the character _M_ would only appear in the male because it only develops in association with _XX_ in the somatic cells descended from the male zygote. This would be the result in the first generation in which a somatic modification affected the factors in the chromosomes. In the next generation _m_ in the male would be affected, and the male for the sake of simplicity might be supposed to become _MMXX_. When the female gametes segregated, some would always be _mY_, and some zygotes therefore _MXmY_. Others might be _MMXY_. On this theory, therefore, there would always be some females heterozygous for the male character. Geoffrey Smith, one of the many promising young scientific investigators whose careers were cut short in the War, maintained views concerning somatic sex-characters different from that which explains their development as due to a hormone from the testis or ovary. Nussbaum in 1905 [Footnote: 'Ergebuisse der Anat. und Entwicklungsgesch.,' Bd. xv.; _Pflügers Archiv_, Bd. cxxvi, 1909.] had recorded experiments on _Rana fusca_ (which is identical with the British species commonly called _R. temporaria_) which appeared to prove that in the male frog after castration the annual development of the thumb-pad and the muscles of the fore-leg does not take place, and if these organs have begun to enlarge before castration they atrophy again. When pieces of testis were introduced into the dorsal lymph-sac of a castrated frog the thumb-pads and muscles developed as in a normal frog. Geoffrey Smith and Edgar Schuster [Footnote: _Quart Journ. Mic. Sci_., lvii, 1911-12.] investigated the subject again with results contrary to those of Nussbaum.