94 ESSAY ON CLASSIFICATION 



which is peculiar to certain Insects, in which several generations of 

 fertile females follow one another before males appear again. 



What comprehensive views must physical agents be capable of 

 taking, and what a power of combination must they possess, to be 

 able to ingraft all these complicated modes of reproduction upon 

 structures already so complicated! — But if we turn away from mere 

 fancies and consider the wonderful phenomena just alluded to in all 

 their bearings, how instructive they appear with reference to this 

 very question of the influence of physical agents upon organized 

 beings! For here we have animals endowed with the power of multi- 

 plying in the most extraordinary ways, every species producing new 

 individuals of its own kind, differing to the utmost from their 

 parents. Does this not seem at first as if we had before us a perfect 

 exemplification of the manner in which different species of animals 

 may originate, one from the other, and increase the number of types 

 existing at first? And yet, with all this apparent freedom of trans- 

 formation, what do the facts finally show? That all these transforma- 

 tions are the successive terms of a cycle, as definitely closed within 

 precise limits as in the case of animals, the progeny of which re- 

 sembles for ever the immediate parent in all successive generations. 

 For here, as everywhere in the organic kingdoms, these variations 

 are only the successive expressions of a well regulated cycle, ever 

 returning to its own type. 



SECTION XXI 

 SUCCESSION OF ANIMALS AND PLANTS IN GEOLOGICAL TIMES 



Geologists hardly seem to appreciate fully the whole extent of the 

 intricate relations exhibited by the animals and plants whose re- 

 mains are found in the different successive geological formations. I 

 do not mean to say that the investigations we possess respecting the 

 zoological and botanical characters of these remains are not re- 

 markable for the accuracy and for the ingenuity with "\vhich they 

 have been traced. On the contrary, having myself thus far devoted 

 the better part of my life to the investigation of fossil remains, I 

 have learned early, from the difficulties inherent in the subject, better 



