MYEIAPODA. 97 



weight iu a less dense and buoyant element, so that, 

 when removed from their native waters, they are 

 utterly helpless and impotent. Supposing, as a 

 matter of mere speculation, it was inquired, by what 

 means animals so constructed could be rendered 

 capable of assuming a terrestrial existence, so as to 

 seek and obtain their food upon the surface of the 

 earth, and thus represent uix>n land the Annelidans 

 of the ocean ; a little reflection would at once indi- 

 cate the grosser changes required for the attainment 

 of such an object. To convert the water-breathing 

 organs of the aquatic worms into an apparatus 

 adapted to breathe the air Avoukl be the first requi- 

 site. The second would be to give greater firmness 

 to the tegumentary skeleton, to allow of more 

 powerful and accurately applied muscular force, by 

 diminishing the number of the segments, and by 

 converting the lateral oars into jointed limbs, suffi- 

 ciently strong to sustain the Avhole weight of the 

 body, to provide instruments of locomotion fitted for 

 progression upon the ground. Yet all these changes 

 would be inefficient without corresponding modifica- 

 tions in the nervous system. The lengthened chain 

 of minute ganglia, met with in the leech (Fig. 57), 

 would be quite inadequate to wield muscles of strength 

 adapted to such altered circumstances; the small 

 brain would be incompetent to correspond with more 

 exalted senses ; so that, as a necessary consequence 

 of superior organization, the nervous centres must all 

 be increased in their proportionate develoj^ment, to 

 adapt them to higher functions. The changes Avhich 

 our supposition infers would be requisite for the con- 

 version of an aquatic Annelid into a Myriapod, are 

 precisely those which we encounter. The air- 

 breathing animals w'hich we have now to describe 

 form the transition from the red-blooded worms to 

 the class of insects, and are intermediate between 

 these two great classes in every part of their struc- 

 ture. The body of a myriapod consists of a consecu- 

 tive series of segments of equal dimensions, but un- 



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