196 THE BOOK OF NATURE STUDY 



active larvae of, say, gnats and harlequin-flies, to put them in a deep 

 aquarium vessel, and to watch their wonderful metamorphoses. 



The River. Many of the hints which we have given in 

 regard to the pond will apply also to the river. It is important 

 to choose a stretch with some variety, here a deep slowly flowing 

 reach with reeds and flags by the waterside, there a shallow 

 quickly flowing reach with plenty of stones to be turned over. 



As to the higher animals, there is still the possibility in some 

 parts of the country of seeing an otter (Lutra vulgar is), or of 

 finding a trout lying by the side of the stream with a great gash 

 at its neck where the otter had begun to eat. It need hardly be 

 said, however, that the probabilities of seeing an otter are as 

 few as those of seeing a " water-rat " are many. But there is 

 abundance of educational material even in these "rats/*- the 

 first step being to learn to see with precision, to distinguish the 

 brown rat (Mm decumanus), which is often about the banks, from 

 the water-vole (Microtus amphibius), and thus to make it clear 

 that we have not in Britain any animal that can be accurately 

 called a " water-rat/' except with the same licence as might be 

 shown if one called a fox a wild dog. Precision of words is ex- 

 pected in our games or on board a yacht ; it is not unreasonable 

 to insist upon it in our science. Then, to return to the river, 

 there is the beautiful water-shrew to look for. 



Riverside Birds. As we walk up the riverside in spring 

 we startle the wary oyster-catchers (Hcematopus ostralegus), 

 which are also frequenters of the seashore, and if we are sharp- 

 eyed we may find their protectively coloured eggs among the 

 gravel. Its shrill Keep-keep is very striking, and so is the colora- 

 tion of the bird black and white plumage, orange-yellow bill, 

 livid flesh-coloured legs and toes. The black-headed gulls (Larus 

 ridibundus\ called laughing-gulls because of their incessant 

 cackling, fish for water insects in the rivers near the " gullery." 

 Now and then we have a chance of seeing a kingfisher, like a flash 

 of rainbow over the stream, but we are almost always sure of 

 coots and water-hens. Very characteristic of rapid mountain 

 streams is the water-ouzel or dipper (Cinclus aquations} , a brown 

 and white bird, often seen perched on a rock in mid-stream. It 



