different a nature to act upon the tissues of the host.

The observation of Geoffrey Smith that eggs may occur in the testis of a
crab after recovery from the parasite appears of more importance than his
peculiar theoretical suggestions, for it tends to show that sex is not
always unalterably fixed at fertilisation. In this case the influence of a
parasite predominantly female would seem to be the real cause of the
development of eggs in the testis of the host. 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.



CHAPTER VI

Origin Of Non-Sexual Characters: The Phenomena Of Mutation


According to the theory here advocated, modifications produced by external
stimuli in the soma will also be inherited in some slight degree in each
generation when they have no relation to sex or reproduction. In this case
the habits and the stimuli which they involve will be common to both
sexes, and the hormones given off by the hypertrophied tissues will act
upon the corresponding determinants in the gametocytes. The modifications
thus produced will therefore be related to habits, and the theory will
include all adaptations of structure to function, but other characters may
also be included which are the result of stimuli and yet have no function
or utility.