118 ESSAY ON CLASSIFICATION 



work entitled Vestiges of Creation^^^ to require further mention 

 here. It has also been shown above (Sect, viii) that animals do not 

 form such a simple series as would result from a successive develop- 

 ment. There remains therefore only for us to show now within what 

 limits the natural gradation which may be traced in the different 

 types of the animal kingdom corresponds to the changes they under- 

 go during their growth, having already considered the relations 

 which exist between these metamorphoses and the successive appear- 

 ance of animals upon earth, and between the latter and the struc- 

 tural gradation or relative standing of their living representatives. 

 Our knowledge of the complication of structure of all animals is 

 sufficiently advanced to enable us to select, almost at random, our 

 examples of the correspondence between the structural gradation of 

 animals and their embryonic growth in all those classes the embryo- 

 logic development of which has been sufficiently investigated. Yet 

 in order to show more distinctly how closely all the leading features 

 of the animal kingdom are combined, whether we consider the com- 

 plication of their structure, or their succession in time, or their 

 embryonic development, I shall refer by preference to the same 

 types which I have chosen before for the illustration of the other 

 relations. 



Among Echinoderms, we find in the order of Crinoids the pe- 

 dunculated types standing lowest, Comatulas highest, and it is well 

 known that the young Comatula is a pedunculated Crinoid, which 

 only becomes free in later life. J. Miiller has shown that among the 

 Echinoids, even the highest representatives, the Spatangoids, differ 

 but slightly in early youth from the Echinoids, and no zoologist 

 can doubt that these are inferior to the former. Among Crustacea, 

 Dana has insisted particularly upon the serial gradation which may 

 be traced between the different types of Decapods, their order being 

 naturally from the highest Brachyura, through the Anomoura, the 

 Macroura, the Tetradecapods, etc., to the Entomostraca; the Ma- 

 crouran character of the embryo of our Crabs has been fully illus- 

 trated by Rathke, in his beautiful investigations upon the embry- 



^*^ [Robert Chambers was the author of Vestiges of the Natural History of Creation 

 and Explanations: a Sequel to "Vestiges of the Natural History of Creation" (London, 

 1846), books whose theories of change and development were opposed by the great 

 majority of professional naturalists including those who would later support Darwin. 

 See the preface by Alexander Ireland to the 1884 (London) edition of the Vestiges.] 



