120 ANIMAL LIFE 



the air passage emancipated from the food passage. 

 The reptiles exhibit a more complete solution of the 

 air-breathing problem. In this, as in all their other 

 faculties, we find amongst them a vast range of medio- 

 crity. Most reptiles are only partially adapted for life 

 on land ; many at regular periods pass into a trance 

 during which they respire mainly by the stores of 

 air which their lungs have previously accumulated. 

 In the reptiles we find the last traces of that primeval 

 animal capacity for surface or skin breathing ; of true 

 gills nothing but the framework remains. But in none 

 of the known groups of this immense class do we find 

 other than simple bag-like lungs, or a larynx capable 

 of modulated sound. In none of them at the present 

 day is the heat produced in respiration so controlled 

 as to ensure a continuously periodic high vitality. 



From some unknown members of this mediocre 

 class two offshoots have sprung in which the 

 faculties of breathing amply, of sustained activity, 

 and of voice production, have been perfected. Among 

 birds we trace the evolution of the most perfect 

 lungs that are known ; of the most continuously active 

 of beings ; of the most indefatigable of songsters. 

 Amongst mammals we can follow the elaboration of 

 a less aerial type of breathing; but, in accordance 

 with their closer touch with the ground and the 

 acquisition of great size, we find in them a means of 

 inspiring and purifying great tides of air, an immense 

 store of latent energy, and the most varied powers of 

 voice and speech. 



