ON THE SUBMERGENCE OF WATER-BIRDS. V 



danger. But farther, when a man attempts to dive, he takes a full inspiration 

 first, and then, when diving, he powerfully exerts all the large muscles round 

 the body, I have little doubt to produce instinctively the same effect that I 

 suppose is produced in the diver, namely, to bring the specific gravity of his body 

 nearer to that of the water, and so make the diving easier. Again, Mr. Atkinson 

 said that a Moorhen shot when diving, instantly rose to the surface, notwith- 

 standing the lead he had put into it. But why? simply because the bird 

 being dead, the act of volition by which it compressed its body was gone, 

 and the contained air instantly assumed its usual bulk, and the bird its usual 

 position. So in the case of any bird diving from fear: it rises to the 

 surface Avith its body in a state of compression; it at first only allows its 

 head and neck to emerge, but on looking round and seeing no danger, it 

 suldenly relaxes the effort which it had till then kept up, and its body instantly 

 resuming its usual state, the bird as quickly assumes its natural position, and 

 floats buoyantly on the 

 water. Let, however, -— ^^^^^fck 

 some slight occui-reiice ^*^^^^|B^ 



disturb it, ]M| ^^^^flHH^^^^^^^ 



to make it dive, and : ;, ^fiujmvm.tim m ^^^^ ^ ^^Z=,-^ ^ if y -^^^^^B^^si:r-^ 

 it instantly sinks itself ^^ ^^^^mu^B^l^tiSSl^^^S^^^^- 

 decper into the water, .T^^^^^^^^^B^^^^^^^^^^^^H^^^^^- 

 and remains submerged ^^^^Hj^^^^l^l^^^^^^^^^lHllB^^^F^ 

 until it finds that all "^^^^^^^^^^^^^^^^bB^^^^^^^^C? 



danger has disappeared. - ^^^^ssisr ^-'^^^^^S S ^^^^^"''^'^ "^-^ '^'?^ 



It runs no risk of being 



suffocated, for the condensed air is just as capable of sustaining life as 

 ordinary air, and will do so just as long as a common inspiration. The bird 

 too in this compressed state is able to inspire regularly, though, of course, in a 

 constrained manner. 



Let us now take one illustration from another class of Nature's works — I 

 mean the Paper Nautilus. The shell occupied by this curious animal is of 

 considerable size, but has only a small portion of its cavity filled by the body 

 of the animal. The rest of the shell is composed of cells, with the interior 

 of each of which, however, the animal has a direct communication by means 

 of what is called the siphuncle or tube. These cells in their natural state 

 are filled with air or gas of some kind; and it is clear that in this condition 

 the animal must float on the surface of the water, and cannot while in that 

 state sink. But there is a very curious provision to obviate this inconvenience, 

 for as soon as the animal is frightened, or from any other cause, con- 

 tracts its body within the front part of the shell, water is by this very act 

 forced down the tube, and so into all the cells, and thus compressing the 

 air, the buoyancy of the animal is lessened, and it sinks in the water. When 

 the animal wishes to rise, it protrudes the head, and this opens the com- 

 munication between the cells and the external water, and the air expanding 

 forces out the water, and the animal again floats. Here we find an action 



VOL. I. C 



