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No cases of mutation or gametogenic variation hitherto described exhibit a similar metamorphosis or recapitulation. Secondary sexual characters, usually in the male sex, correspond in their development with the development of maturity and functional activity in the gonads, and it has been proved that the latter influence the former by means of 'hormones' or internal secretions.
In Lepidoptera among insects the evidence concerning castration tends to prove that hormones from the gonads play no part at all in the development of somatic sexual characters. Exper. Zool. Oudemans had previously obtained the same result in the Gipsy Moth, Limantria dispar.
Mumps is a sickness that sometimes permanently injures the gonads: the testes or ovaries. The thyroid dominant, whose system is rich in thyroid, will rarely suffer from any of the common diseases of children if at all, from measles. Op the other hand, those who have every infection of the period, and who, as their mothers say, seem to get everything, are those whose system is thyroid poor.
Such a conclusion inevitably suggests that the investigator is proving too much. The subject of the influence of hormones from the gonads is mentioned, but not fully discussed, in a volume by Dr. Origin Of Somatic Sex-Characters In Evolution
He claims by transplantation of the gonads in young rats and guinea-pigs to have feminised males and masculised females. The females are smaller, and hare finer, softer hair than the males. The testes were removed and ovaries implanted in young males. The animals so treated grew less than the merely castrated specimens, and therefore when full-grown resembled females in size.
This fact, together with a number of others, make clear that while the gonads may be the jeune premier of the drama, the vitality of the plot depends upon the other endocrines. Since old age is an exhaustion, permanent and irreparable of all the members of the ductless gland directorate, the reason becomes clear for the temporary quality of the rejuvenation effected by the procedures of Steinach.
Hermaphrodite animals, as has been pointed out by Correns and Wilson, cannot be brought under this scheme at all. In the earthworms, for instance, we have, in every individual developed from a zygote, ova and spermatozoa developing in different gonads in different parts of the body. The differentiation here, therefore, must occur in some cell-division preceding the reduction divisions.
The theory of the heredity of somatogenic modifications by means of hormones harmonises with and goes far to explain the facts of metamorphosis and recapitulation in adaptive characters, and also the origin of secondary sexual characters, their correlation with the periodical changes in the gonads and the effects of castration.
The theory proposed by me in 1908 was that we have within the gonads numerous gametocytes whose chromosomes contain factors corresponding to the different parts of the soma, and that factors or determinants might be stimulated by products circulating in the blood and derived from the parts of the soma corresponding to them.
Geoffrey Smith does not discuss the origin of the somatic sexual characters in evolution, or attempt to show how his theories of sexual formative substance, and of the influence of the gonads by subtraction rather than addition, would bear upon the problem. Origin Of Non-Sexual Characters: The Phenomena Of Mutation
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