CHAPTER XII 

 CRUSTACEA OF THE PAST 



INCE the acceptance by naturalists of the theory 

 of Evolution as indicating the mode of origin 

 of the various forms of life now existing, one of 

 the chief lines of biological investigation has had 

 for its object the reconstruction of the pedigree (or, 

 as it is called, the " phylogeny ") of the larger groups 

 of the animal and vegetable kingdoms. In attempt- 

 ing to do this, there are three main sources from 

 which evidence may be drawn. The results of Com- 

 parative Anatomy enable us to decide with more or 

 less confidence as to the degrees of relationship 

 between the groups of organisms, and to distinguish 

 between the more primitive and the more specialized; 

 the study of Embryology is, at least, an indispensable 

 adjunct to Comparative Anatomy, even if it does not, 

 as was once supposed, give us an actual recapitula- 

 tion of ancestral history ; and, finally, the study of 

 Fossil Remains holds out the hope that we may be 

 able to find the ancestral types themselves. 



It is clear that evidence from the last-named 



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