575.1 235 
I 
The Fundamental Principles of Heredity 
N the recent elaboration of the Theory of Descent, as first fully 
published by Charles Darwin, two schools of thought have 
arisen. The one, though professing discipleship pure and simple, 
has laid extreme stress on the principle of Natural Selection, which 
owes so much to Darwin, but has rejected his belief in the 
internal tendencies of races to vary in adaptation to changed 
surroundings; while the other has attributed the greater share in 
the transformation of species to the latter factor, and sent Natural 
Selection in the background. The two most illustrious leaders 
of scientific thought have been August Weismann on the one side 
and Herbert Spencer on the other. Their debates have long since 
obtained an audience among the cultured laity; but while the 
arguments are well known, some of the most important facts have 
been rather taken for granted than fully stated and clearly co-or- 
dinated even in the scientific press. I allude especially to the 
coarser relations of the actual mechanism of reproduction and of 
the act of transmission from one generation to the next of the 
form which clothes on or assumes the parental characters. Such 
an exposition as we have to make cannot be limited to the higher 
organisms which are familiar to us in our daily life, for these are 
complex elaborations ; while the primitive types, though still existing 
abundantly, are only to be studied with the microscope. It is in 
this field, hidden if not buried, that we must first labour, if we wish 
to rightly understand the foundations of the wonderful superstructure 
of the higher Organic Kingdoms. We shall endeavour to use as 
few unfamiliar terms as possible, bearing in mind that the reader 
has‘no Handy Atlas to help him in following the exploration of this 
foreign country, with its outlandish names. 
Only two centuries ago the microscope revealed to mankind an 
immense world of minute living creatures as well as the details of the 
structure of the familiar Animal and Plants. Naturally enough 
the early observers, or ‘ philosophers, as they were then called, 
inferred that these strange small creatures must have as complex 
a structure as our own. ‘They proceeded zealously to search 
for, and sometimes to proclaim, the existence therein of brain, 
heart, blood-vessels, etc., just like those of ordinary bird, beast, or 
R 
