6o Thomas Henry Huxley 



here, it is necessary to say that merely as a series of 

 intricate anatomical descriptions and comparisons, this 

 memoir was one of the most valuable of any that Hux- 

 lej^ wrote. The working out of the theory of the 

 archetj'pe is peculiarl}' interesting to compare with 

 modern conceptions. To those of us who began bio- 

 logical work after the idea of evolution had been im- 

 pressed upon anatomical work, it is very difficult to 

 follow Huxley's papers without reading into them evo- 

 lutionary ideas. In the article upon Mollusca, written 

 for the ninth edition of the Encyclopcvdia Britajmica, by 

 Professor Ra\' lyankester, the .same device of an arche- 

 typal or, as Lankester calls it, a schematic mollusc, is 

 employed in order to explain the relations of the differ- 

 ent structures found in different groups of mollu.scs to 

 one another. Lankester's schematic mollusc differs 

 from Huxlej^'s archetypal mollusc onlj- as a finished 

 modern piece of mechanism, the final result of 3'ears of 

 experiment, differs from the original invention. The 

 method of comparing the schematic mollusc with the 

 different divergent forms in dift'erent groups is identi- 

 cal, and yet, while the ideas of Darwin are accepted in 

 ev^er}' line of lyankester's work, Huxley was writing 

 six 5'ears before the publication of The Origin of Species. 

 There was growing up in Huxley's mind, partly from 

 his own attempts to arrange the anatomical facts he dis- 

 covered in an intelligible .series, the idea that within a 

 group the divergencies of structure to be found had 

 come about by the modification of an original t)'pe. 

 Not only did he conceive of such an evolution as the 

 only possible explanation of the facts, but he definitely 

 used the word evohition to convey his ideas. On the 

 other hand, he was firmly convinced that such evolu- 

 tion was confined within the great groups. For each 



