COLOURS OF THE FEATHERS OF BIRDS. 



21 



As to land animals, some take in and again eject air, which is called 

 inspiration and expiration, asman,andall such land animals ashavelungs. 



Others again do not take in the air, but live and have their food in 

 the earth, as wasps, bees, and insects. Now I denominate those ani- 

 mals insects, which have incisions in their body, either in the upper 

 parts, or in both these, and also in the under parts. Many land ani- 

 mals, as we have said, obtain their nutriment in moisture; but no water 

 animal which takes in the sea water, derives its aliment from the earth. 



Some animals, however, first live in moisture, but afterwards change 

 into another form, and live out of moisture, as is the case with mag- 

 gots in rivers, from which a fly is produced. 



Some animals again do not change, while others are changeable; 

 the former live in moisture ; but no land animal is of this kind, while 

 many that dwell in moisture live fixed to rocks, as many kinds of shell- 

 fish. The sponge also appears to have a certain sense ; an indication 

 of which is, that it is with greater difficulty torn off, as they say, unless 

 the motion by which it is wrenched away is performed when it is 

 unaware of danger. But some adhere to rocks, which they occasion- 

 ally leave, such as is a certain genus called the sea anemone. For 

 some of these feed by night away from the rock. Many also, when 

 they are liberated, are without motion, as oysters, and the spongy crea- 

 tures called holothuria. But some have a power of swimming, as 

 fishes, the mollusca, and those animals that are covered with a soft 

 shell, such, for instance, as locusts. Some likewise are able to walk, 

 as the genus of crabs; for this animal lives naturally in the water, 

 while it has also the power of walking. 



ON THE COLOURS OF THE FEATHERS OF BIRDS. 



BY EDWARD BLYTH, 



Every bird, after the species has been produced, annually under- 

 goes in the autumn a complete change of plumage, which is com- 

 monly termed moulting. Some species undergo, or partially undergo, 

 this change twice in the year — in autumn and in the spring ; as is the 

 case with a variety of aquatic birds. Others again, as the ptarmigan 

 or white grouse, seem to be in a perpetual moult ; that is to say, new 

 feathers may always be observed amongst their plumage. It is probable 

 that, in this case, new feathers are thrown out in an unusually short 

 space of time ; thus enabling the bird to meet the sudden changes of 

 temperature, common in the elevated regions in which it is found, — 

 a beautiful provision for an Alpine climate. 



