STUDIES IN ANIMAL LIFE. 27 



in many animals, and is often mistaken for a system 

 of blood-vessels. In one sense this is correct, for 

 these branching tubes are carriers of nutriment, and 

 the only circulating vessels such animals possess; 

 but the nutriment is chyme, not blood : these simple 

 animals have not arrived at the dignity of blood, 

 which is a higher elaboration of the food, fitted for 

 higher organisms. 



Thus may our frog, besides its own marvels, af- 

 ford us many " authentic tidings of invisible things," 

 and is itself a little colony of life. Nature is eco- 

 nomic as well as prodigal of space. She fills the il- 

 limitable heavens with planetary and starry grand- 

 eurs, and the tiny atoms moving over the crust of 

 earth she makes the homes of the infinitely little. 

 Far as the mightiest telescope can reach, it detects 

 worlds in clusters, like pebbles on the shore of in- 

 finitude ; : deep as the . microscope can penetrate, it 

 detects life within life, generation within genera- 

 tion, as if the very universe itself were not vast 

 enough for the energies of life ! , 



That phrase, generation within generation, was 

 not a careless phrase ; it is exact. Take the tiny 

 insect {Aphis) which, with its companions, crowds 

 your rose-tree ; open it, in a solution of sugar-water, 

 under your microscope, and you will find in it a 

 young insect nearly formed ; open that young in- 

 sect with care, and you will find in it, also, another 

 young one, less advanced in its development, but 

 perfectly recognizable to the experienced eye ; and 



