SIGHT — FIELDWORK AND EXPERIMENTS 35 



we come to deal with the sense of touch. However, I think 

 it may be appropriate here to say a Uttle about observations 

 on captive creatures when field observations are not readily 

 to be made. 



I think that in certain cases it is quite permissible to carry 

 out observations and experiments with animals in captivity 

 when it is unlikely that in the field the observations could be 

 carried out at all. The key to success is to make sure that the 

 conditions under which one's captive creatures are housed 

 resemble as closely as possible the correct natural habitat. 

 A well-balanced aquarium for observations on small fishes 

 or other aquatic life is a good example of this. 



To return to spiders : if the student wishes to see for him- 

 self how a spider of a suitable kind uses its eyes, there can 

 be no better way of doing this than by catching some water 

 spiders from a pond and then keeping them in a small 

 aquarium well planted with weeds and supplied with water 

 from the pond of origin. These spiders will adapt themselves 

 very well indeed to aquarium life and will not only feed but 

 will breed under these conditions. They would do neither if 

 the place of captivity were not satisfactory, and so the student 

 can be confident that any observations he may make will be 

 worth while and his conclusions will be well based. 



Amphibians 



I have found that amphibians are very profitable for use in 

 sense observations, and it is easy to discover the way in 

 which frogs, toads and newts use their eyes in getting food. 

 The Common Frog, being so agile, is unsatisfactory to watch 

 in the field not only because most of its feeding is done at 

 dusk or at night, but because this frog, being terrestrial once 

 its breeding season is over, is not always easy to locate. This 

 being the case it is better to rely on a captive frog or two for 

 one's investigations. It is frequently said that Common Frogs 

 are difficult and even impossible to keep in captivity for any 

 length of time. In the laboratory this may be so because, as 

 far as my own experiences of seeing frogs in other people's 

 laboratories are concerned, they are often housed in a tank 

 with nothing but a few inches of water at one end and some 



