104 
Proceedings of Royal Society of Edinburgh. [sess. 
its nucleus half of the male and half of the female nuclear elements, 
and it is possible that this marvellously exact dualism persists 
throughout. 
Most hopefully, perhaps, has the continuity been expressed by 
several, e.g ., Berthold, Gautier, and Geddes, in chemical terms. In 
the paper by the last mentioned on “Growth, Sex, Reproduction, and 
Heredity,” the following weighty sentence occurs: — “If the repro- 
ductive elements start with a specific protoplasm continuous with that 
of the combined mother ovum and fertilising sperm — that is, with a 
concentrated accumulation of characteristic anastates and katastates 
— the simple fact that the products of protoplasmic change must be 
fixed, definite, and continuous, as in all chemical processes, gives 
us at once a protoplasmic basis from which to explain the constant 
and necessary symmetry of segmentation and development.” The 
views of Berthold are closely similar. Inheritance is possible only 
on the basis of the fundamental fact that in the chemical processes 
of the organism “ the same substances and mixtures of substances 
are reproduced in quantity and quality with regular periodicity.” 
Gautier discusses both variation and heredity from a chemical point 
of view. “ The force which maintains the species, and gives it the 
character of constancy and resistance, is nothing more than the 
resultant of the forces which maintain the chemical species of which 
the organism is composed.” 
YI. The Problem of Reconstruction. 
The doctrine of the continuity of the reproductive protoplasm 
obviously answers not only the first problem of the uniqueness of 
the germ-cell, but it casts a new light upon the problem of recon- 
struction. The problem is simplified, and, to a certain extent, 
disappears. Why should the germ-cell divide, redivide, and build 
up an embryo in the precise way in which it does ? Because it is 
virtually continuous with the parent germ, which behaved in a pre- 
cisely similar fashion. Thus the question ceases to be particular, 
and becomes general — ceases, in fact, to be a problem in heredity, 
and becomes a subject for investigation under the mechanics of 
development. 
This, it need hardly be said, is to refer to a field of investigation 
which has been but little worked. In spite of the luminous sugges- 
