372 THE BEGINNINGS OF LIFE. 



on the all-important blood current. The organism 

 which but a minute before was living, is now dead, 

 dead that is as an organism, as a marvellous 

 mechanism, capable, perhaps, of performing the highest 

 functions of humanity; but the matter is still there, 

 and in a c living ' state, even though the organism as a 

 whole is dead and spiritless. The nerve will still for a 

 time transmit a stimulus, the muscle will still contract 

 the cilia of various mucous membranes still lash on, as 

 though no change had taken place. But in descending 

 step by step from highest animal to lowest animal, 

 and though far less obviously from highest plant to 

 lowest plant, we find the organism less and less com- 

 plex, and, at the same time, we find the nexus less 

 obvious which binds their several parts into one whole. 

 And at last we meet with organisms altogether simple, 

 or else made up of mere repetitions of similar parts, 

 so that the individualizing nexus is reduced to its 

 lowest terms, and the separate parts live and die. more 

 or less independently. 



The great difference existing between a layer of 

 ciliated epithelium on the human trachea ] , and an ex- 

 pansion of more or less similar cellular compartments 

 constituting one of the ulva-like Algas, is due to the 

 fact that the former has been produced in a situation 

 and under the influence of a set of conditions so much 

 more complex than those which have given birth to the 

 Alga, that its structure is, to a corresponding extent, 



1 See vol. i. p. 145, Fig. 4. 



