292 Proceedings of Royal Society of Edinburgh. [april 2, 
projectional construction. After having drawn or photographed the 
body before it was cut into sections, and after having reproduced on 
the same scale its different sections, we can obtain front or side views 
of every internal part by the aid of the compasses. Knowing the 
scale of magnification of our drawings, and the thickness of the 
sections, having also the middle line, the dorsal line, or some arti- 
ficial mark as base lines for our measurements, we are possessed of 
all the elements necessary for a precise reconstruction of the anatomy 
of the object. The combination of the different reconstructions and 
sectional views will give us a plastic idea of the body in question, 
and will enable us to reproduce it in wax or in some other suitable 
material. 
During the last twenty years I have been indebted to the methods 
of projectional and plastic reconstruction for a very large amount of 
information. Gradually these methods have also found other sup- 
porters, and recently they have been completed and improved by 
younger workers, for example, Drs Born, Selenka, Kastschenko, and 
Strasser. 
For the solution of certain questions, we need not only the recon- 
struction of the anatomical forms, but also the determination of the 
volume of a body and of its parts. By a planimeter we determine 
the area of the individual sections. The multiplication of these 
values by the respective thicknesses gives the volumes of the 
sections, and the total volume of the body is found by addition of 
the partial values. A few good determinations of volume cut short 
numbers of confusions and tedious discussions. 
Observation shows a very frequent coincidence of the development 
of a germ with its increase of volume. We are therefore easily 
disposed to regard it as a general law, and to regard every develop- 
ment as associated with increase in volume. The question is not a 
simple one. Extensive phases of embryonic formation may occur 
without increase in volume. The germ of a salmon, immediately after 
segmentation, has a cake-like form and a volume of about 0’5 cub. 
mm. After the embryo has been formed by a series of transforma- 
tions, and after the yolk has been surrounded by the yolk sac, the 
volume of the embryo with the yolk sac membrane is not more than 
before, namely, about 0‘5 cub. mm. The embryo has been formed 
from the segmented germ without any increase in volume, only by 
