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 mirror, 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, or 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 



