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THE AMERICAN NATURALIST [Vol. XLVI 



The combinations of these characters that are found are as follows: 

 Opisthocosmia ornata: AbcDEF. 



insignis: ABcDEf. 

 longipes: AbCDEf. 

 tenella: AbCdef. 

 minuscula: aBCDEf. 

 Other species occur, in other countries, showing a different combina- 

 tion of characters, and there are characters not contained in this list, 

 which is purposely reduced to a simple form; hut the same principles 

 apply generally. 



The bearing upon evolution of the fact that species are varying com- 

 binations of relatively few characters is mot important. Combined 

 with the fact of hybridization it indicates that the main problem of 

 evolution is that of the origin of specific characteristics. A character, 

 once arisen in an individual, may become a part of any species with 

 which that individual can hybridize. Given the successive origin of the 

 characters J. B, C, D, E, F, in various individuals capable of inter- 

 generating with the mass of the species, it is clear that such characters 

 would in time become similarly combined on many individuals; and the 

 similar individuals, taken together, would constitute a new species. The 

 adjustment of the species would be perfected by the elimination of such 



Second, modern studies have taught us that we have 

 regarded the steps of progress in evolution in too crude 

 a way. One school adhered to the view that characters, 

 as we know them in the adult, arose gradually in phy- 

 togeny as in ontogeny, i. e., that the germ-plasm under- 

 goes a development as the child does. Another school 

 proclaimed for discontinuity in phytogeny; i. e., that the 

 conditions in or the constitution of the germ-plasm un- 

 dergoes from time to time more or less abrupt changes. 

 Such abrupt changes are not altogether unknown in 

 ontogeny ; for the sundering of a chromosome or the per- 

 foration of a membrane involves essentially abrupt or 

 discontinuous processes. The new era of experimental 

 breeding is leading us to a position that is in some 

 respects intermediate between the views of these two 

 schools. We have discovered a hitherto unsuspected 

 multiplicity of inheritable units, indicating a vaster com- 

 plexity of the system of determiners in the germ-plasm 



