xii INTRODUCTION 
swimming free in natural environments, and illuminated 
as in nature. For this purpose I have constructed a 
special pond, and fish turned into it in a few days are 
quite as much at home as in the waters they came 
from. A glance at the photograph of this pond, 
taken during the course of its construction, and before 
it was filled with water, will show quite clearly how it 
works. 
The bottom and sides are of concrete. In one 
wall of the pond is a large open space, which communi- 
cates with an observation chamber, and between this 
chamber and the water in the pond is a sheet of plate 
glass. Concealed in the chamber, the observer can 
watch the fish as they appear to each other in the 
water. In consequence of the darkness in the chamber 
and the light in the pond, the glass is converted into 
a murror, and the fish merely sees himself and his sur- 
roundings reflected, while the observer can plainly see 
into the pond. It is thus possible to observe a timid 
fish without disturbing him. 
In addition, an instantaneous photograph can be 
taken of moving fish under three feet of water. 
Photography of fish in the pond described is only 
one of the methods of obtaining illustrations, as shown 
in the present book. To show structure and colour 
arrangement, .r when it is desired to make the fish 
conspicuous, the specimen is photographed in a large 
glass tank. These tanks have in them growing 
weeds, natural food, and running water, but the main 
