xiv Introduction 



ready that all backboned animals passed through certain 

 regular and definite stages in their progress from the 

 embryo to the adult state, but Huxley showed that all 

 backboned animals passed through the medusa:; stage, that 

 is, they also exhibited two corresponding " foundation- 

 membranes." He had thus laid a foundation on which 

 other scientists were soon to build. 



Another original view appeared in The Cell Theory 

 (1853). Before this time scientists had believed, as many 

 still believe, the cell to be the ultimate life-unit. In 

 other words, the cell was life reduced to its lowest terms. 

 It was the smallest particle of life just as the atom is con- 

 sidered the smallest particle of matter. Huxley contended 

 that the real life-element was not the cell but protoplasm, 

 that protoplasm was the raw stuff that built up the cell 

 just as the cell built up the body. He compared proto- 

 plasm to the sea, cells to the numberless shells and weeds 

 that the sea tosses up. While this theory has not been 

 universally accepted it has not been conclusively over- 

 thrown. 



But perhaps Huxley's best claim to popular recognition 

 as a scientist is that he discovered, or at least was the first 

 to announce, the pedigree of the horse. In 1870 he said 

 that if there were strong reasons to believe that our mod- 

 ern one-toed horse had a remote ancestor with three toes, 

 there were still stronger reasons to believe that he had 

 a still more remote ancestor with five toes. When Hux- 

 ley visited America in 1876, Professor O. C. Marsh of 

 Yale University showed him the fossil of a horse with 

 four complete toes on the front leg and three on the hind 

 leg. Huxley now re-affirmed his theory of a five-toed 

 horse, " in which, if the doctrine of evolution is well- 

 founded, the whole series must have taken its origin." 

 Two months later Professor Marsh actually discovered the 



