Evolution before Darwin 6i 



group there was a typical structure, and modifications 

 by defect or excess of the parts of the definite archetype 

 gave rise to the different members of the group. More- 

 over, he confined this evolution in the strictest possible 

 way to each group ; he did not believe that what was 

 called anamorphosis — • the transition of a lower t3'pe 

 into a higher type — ever occurred. To use his own 

 words : 



"If, however, all Cephalous Mollusca, i. e., all Cephalopoda, 

 Gasteropoda, and Ivamellibraucbiata, be ouly modificatious by 

 excess or defect of the parts of a definite archetype, theu, I 

 think, it follows as a necessary consequence, that no anamor- 

 phosis takes place in this group. There is no progression 

 from a lower to a higher type, but merely a more or less com- 

 plete evolution of one type. It may indeed be a matter of very 

 grave consideration whether true anamorphosis ever occurs in 

 the whole animal kingdom. If it do, then the doctrine that 

 every natural group is organised after a definite archetype, a 

 doctrine which seems to me as important for zoology as the 

 theory of definite proportions for chemistry, must be given up." 



It is of great historical interest to notice how closely 

 actual consideration of the facts of the animal kingdom 

 took zoologists to an idea of evolution, and yet how far 

 the^^ were from it as we hold it now. It is fashionable 

 at the present time to attempt to depreciate the immense 

 change introduced b}^ Darwin into zoological specula- 

 tion, and the method employed is largely partial quota- 

 tion, or reference to the kind of ideas found in papers 

 such as this memoir b}' Huxle3^ The comparison be- 

 tween the types of the great groups and the combining 

 proportions of the chemical elements shows clearly that 

 Huxley regarded the structural plans of the great 

 groups as properties necessary and inherent in these 

 groups, just as the property of a chemical element to 



