ANIMALS ADAPTED FOR AIR AND WATER BREATHING 345 



conversely, an air-breathing animal if submerged beyond a certain period invariably drowns. Time is not allowed 

 for a prolonged series of minute accidental modifications such as so-called " natural selection " and evolution 

 require to convert an air-breathing animal into a water-breathing one, and vice versd. Moreover, there could be no 

 possible inducement for any animal to undergo the painful suffocating process which such a change would necessi- 

 tate, especially as the discomfort would have to be endured for ages. If, on the other hand, the changes were sudden 

 the animal would fare no better, as its very existence depends on its structural arrangements for the time being. 

 The only apparent exception to this impossible state of things is when structural changes supervene during develop- 

 ment, but these changes cannot be taken into account in this connection, as they are specially provided for, and 

 animals have no power to alter original endowments either in the young or adult condition. Neither can they be 

 altered by environment, irritability, or extraneous stimulation. 



It is no reply to what is here stated to say that certain water- navigating animals (which are mammals and not 

 fishes) such as the porpoises, whales, seals, &c., and which breathe air, habitually live in the water and can remain 

 submerged for very long periods. This only means that their original structural arrangements are expressly 

 designed and modified to meet the peculiar requirements of water transit, and air-breathing. In other words, they 

 are provided with fish-shaped bodies, swimming tails, swimming fins, flippers, and feet, and air-breathing lungs. 

 All these animals if kept long enough under water would be drowned. Similar remarks, but in another direction, 

 are to be made of animals which are water-breathers, such as eels, the chmbing perch, mud-fish, &c., which temporarily 

 leave the water and make excursions on the land. They, in turn, if kept too long out of the water, would inevitably 

 perish. Nor is the situation in any degree altered by the fact that certain animals (some insects and the frog for 

 example) begin hfe as water-breathers with natatory organs, and ultimately become air-breathers with legs adapted 

 for walking, leaping, &c. In all such cases there must be absolute conformity to the conditions involved in water 

 and air breathing and water and land transit respectively. The air-breather must be provided with lungs or their 

 equivalents ; and the water-breathers with gills or branchiae. To this there is no exception. Tadpoles drown 

 if kept in a smooth glass basin of water with no resting-places above the water during the transition stages, that is, 

 when they are shedding their gills and tail, and before they have acquired lungs and legs. The development of the 

 frog afiords a good example of conformity to the air-breathing, swimming, walking, and leaping types. In the 

 tadpole stage the frog is fish-shaped, is provided with a swimming tail, and has no legs. In the adult condition it 

 has no tail, and is provided with four powerful legs which enable it to make considerable progress on land, and also 

 to swim in the water. 



It will be noticed that in the development of the frog, spontaneous and independent structural changes take 

 place according to a predetermined plan, and that no modification in function either as regards the nature of the 

 breathing or the kind of locomotion can occur until the necessary structural changes are completed. A change of 

 structure in every instance precedes a change in function. 



All this was a priori to be expected. The land, water, and air materially differ from each other, but as they 

 form the abodes, and provide the highways along which animals progress in pursuit of food and other physical advan- 

 tages, the animals themselves must correspondingly differ. It is absolutely necessary to draw a line of demarcation 

 as between water and air breathing animals, and between animals specially constructed to walk, swim, and fly. 



As the land differs from the water, and the water from the air, so must the animals differ from each other 

 according as they are designed to live and move on the land, on and in the water, and in the air. The animals and 

 their travelUng organs are specially modified to meet the diverse conditions. They are adapted to their particular 

 work, and there is a co-ordination of parts which prevents accident or mishap in any direction. 



The three highways along which animals progress are material in their nature ; that is, they are composed of 

 physical particles more or less closely aggregated. The number and arrangement of the particles determine the 

 amount of support afiorded to the travelling organs and bodies of animals. Thus in the case of the land, the 

 particles are densely packed together and crowded ; the land, as a consequence, suppUes what is practically a solid 

 basis of support, and an unyielding fulcrum for the travelhng organs of animals. The rule, in land transit, is small 

 feet and heavy bodies. In the case of water, the particles are less numerous and loosely distributed. As a result, 

 the water provides only partial support, and a yielding fulcrum. The rule, in this medium, is bodies of nearly the 

 same specific gravity as water, and large swimming tails. In the case of the air, the particles are comparatively 

 few in number and very widely separated. As a consequence, the air furnishes next to no support, and an 

 exceedingly mobile unrehable fulcrum. The rule in air is light bodies and very greatly expanded wings. It will be 

 observed that the land, the water, and the air provide three different kinds of fulcra on which the travelhng organs 

 and surfaces of animals act when they change position. Further, the size of the travelling organs is determined by 

 the density, rigidity, and resistance afforded by the fulcra. There is, therefore, an unalterable and invariable relation 

 as between' the fulcra afforded by the three highways along which animals progress, and the size and power of the 



VOL. I. " "''■ 



