pregnancy, which are doubtless also due to hormone stimulation, but which
we will not consider here. The most important evidence in O'Donoghue's
paper [Footnote: _Quart. Journ. Mic. Sci_., lvii., 1911-12.] is that
development of the milk glands takes place after ovulation not succeeded by
pregnancy; that is to say, when corpora lutea are formed but no fertilised
ova or foetus are present in the uterus. In one case eighteen days after
heat, the milk gland was in a condition resembling that found in the
stages twenty-four and thirty-six hours after parturition. In another
specimen, twenty-one days after heat, the milk glands were still more
advanced, with distended alveoli and enlarged ducts. The alveoli contained
a secretion which was almost certainly milk, O'Donoghue states that the
entire series of growth changes in these animals up to twenty-one days
after heat in identical with that which occurs in normally pregnant
animals.

O'Donoghue's conclusion is in agreement with that of Basch,[Footnote:
_Monatesschr. f. Kinderh. V._, No. ix., Dec. 1909.] who states that
implantation of the, ovaries from a pregnant bitch under the skin of the
back of a one-year-old bitch that was not pregnant was followed by
proliferation of the mammary glands of the latter. After six weeks the
glands were considerably enlarged, and after eight weeks they were caused
to secrete milk by the injection of extract of the placenta. It has to be
remembered, however, that the milk glands undergo considerable growth,
especially in the human species, at puberty and at every menstruation, or
at oestrus in animals, which correspond to menstruation. In these cases
there is no question of any influence of the foetus, and experiment has
shown that if the ovaries are removed before puberty, the milk glands nor
the uterus undergo the normal development and menstruation does not occur.
According to Marshall to Jolly [Footnote: _Quart. Journ. Exp. Phys._, i.
and ii., 1906.] the symptoms of oestrus in castrated bitches were found to