birds), as shown by the experiments of Giard and Geoffrey Smith on
crabs. A parasite, _Sacculina neglecta_, sometimes drives root-like
growths into the spider crab, causing slow castration. The females thus
desexed do not assume the male type of body, but castrated males vary so
far toward the female type that some lay eggs[3, p.143; 20]. It is the
discovery of such distinctions which makes it necessary to re-examine
all the older biological evidence on the sex problem, and to discard
most of it as insufficiently exact.

The work of Steinach[12, pp.225f.] on rats is another well-known example
of changing sex characters by surgery. Steinach found that an ovary
transplanted into a male body changed its characteristics and instincts
into the female type. The growth of the male sex organs he found to be
definitely inhibited by the ovaries. He went so far as to transplant the
whole uterus and tube into the male body, where it developed normally.
One of the most interesting of his results is the observation of how the
instincts were changed along with the type of body. The feminized males
behaved like normal females toward the other males and toward females.
Likewise they were treated as normal females by the males.

It would be impossible to give here any just idea of the vast amount of
rigid scientific experimentation which has been carried on in this
field, or the certainty of many of the results. Sex is really known,
about as well as anything can be known, to arise from the chemical
causes discussed above. That is, the endocrine explanation is the
correct one.

One of the most significant results of the transplantation experiments
is the evidence that _each individual carries the fundamental bases for
both sexes_. When Goodale changed a male bird into a female as to