again have reverted towards the older belief in the inherited
effects of environment--a belief which, in spite of the arguments of
Weismann and his followers, has never been without its supporters. The
present condition of this part of biology, as of many others, is one of
open-mindedness approaching agnosticism. There is dissatisfaction with
the beliefs which satisfied the preceding generation, and which were
held up almost as dogmas, but there is no clear vision of the direction
in which a truer view may be sought.

Before leaving this side of the subject, reference must be made to one
important aspect of modern work on heredity--that of the inheritance of
'mental and moral' characteristics. As a result of the work of the
biometric school founded by Galton and Pearson, it has been shown that
the so-called mental and moral characteristics of man are inherited in
the same manner and to the same extent as his physical features. Of the
theoretical importance of this demonstration this is not the place to
speak; its practical value is unquestionable, and may in the future have
important effects on sociological problems.

Another notable line of advance, entirely belonging to the period under
review, and chiefly the product of the present century, is seen in the
science of Cytology--the investigation of the microscopic structure of
the cells of which the body is composed. The marvellous phenomena of
cell and nuclear division have revealed much of the formerly unsuspected
complexity of living things, while the universality of the processes
shows how fundamentally alike is life in all its forms. In recent years
great progress has been made in correlating the phenomena of heredity
and of the determination of sex with the visible structural features of
the germ-cells. Weismann attempted a beginning of this over thirty years
ago, but the detailed knowledge of the facts was then insufficient.
Since the discovery of Mendel's Law, a great amount of work has been
done, chiefly in America, by E.B. Wilson and T.H. Morgan and their
pupils, on tracing the actual physical basis of hereditary transmission.
Although the matter is far from being completely known, the results
obtained make it almost indubitable that inherited characters are in
some way borne by the _chromosomes_ in the nuclei of the germ-cells.
The work of Morgan and his school has shown that the actual order in
which these inherited 'factors' are arranged in the chromosomes