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446 LECTURE XVI. 



capacity for further development, so that the actual diversities 

 were conditioned by differences in the primary forms. 



In bringing before you this hypothesis, — for as yet it is no 

 more, — I do so to prove to you that even on the assumption of 

 a gradual development of such types, as we find both in exist- 

 ing and extinct species, we are not led, as so often asserted, 

 to an original unity of the whole organic world ; but that we 

 must, on the contrary, acknowledge that in that abstract unity, 

 termed a cell, there must necessarily have existed an original 

 difference, — such as that existing in the organisms interme- 

 diate between plant and animal. But just in this, as appears 

 to me, lies another reason for the assumption that the organic 

 world might have been developed from such a beginning. If 

 it be difficult to conceive how the great diversity of organic 

 types could have been developed from a common soil ; it can, 

 on the other hand, not be denied that an intrinsic difference in 

 the constitution of this soil may have given rise to the diver- 

 sities of the types sprung from it. 



The theory of the gradual development of types from pri- 

 marily common forms, has recently, with much ingenuity, 

 been advocated by Darwin, after it had been formerly advanced 

 by French and German naturalists, and especially by Lamarck, 

 though in a different form. This theory, as then advanced, 

 certainly found in me a violent and sincere opponent ; but as 

 it is now propounded, I must confess that it appears to 

 me to afibrd, better than any other theory, a clue to the 

 affinity of individual types, and it seems in every respect a 

 step in advance towards the knowledge of truth. When I 

 opposed the doctrine of the gradual transformation of types, 

 I was certainly much prejudiced by received opinions, which 

 obtrude upon anyone engaged in scientific researches. The 

 sharp contrast apparently existing between species, the sys- 

 tematic distribution and strict division of the different groups, 

 must necessarily have a similar infiuence upon a young stu- 

 dent, as that produced by the contrasts which he finds in 

 living characters. And just as jn daily life we gradually be- 

 come convinced that there exist no human beings absolutely 

 good nor absolutely bad, — that life and society oscillate be- 



