326 THE AMERICAN NATURALIST [Vol. XLVIII 



tion of species can not play an important part in the manu- 

 facture of new wild strains. But only in comparatively 

 rare instances have attempts been made experimentally 

 to mate Linnaean species. The dogma of the objective 

 reality and uniform value of the species unit has diverted 

 us from seriously attacking this problem. Just as in the 

 nineteenth century the fixed idea of the immutability of 

 species blocked the progress of the doctrine of evolution, 

 so this dogma now stands in our way, and obstructs the 

 possibility of vision. We need now fully to recognize the 

 fact, which most biologists are ready to admit, that the 

 term species is applied to most heterogeneous groups of 

 individuals, groups of every conceivable size, based on 

 differences that are most diverse in number and impor- 

 tance, often separated from allied groups entirely by the 

 arbitrary judgment of the describer, and depending ulti- 

 mately upon his personal temperament. These groups, 

 as already stated, have been tested in comparatively few 

 instances by the only reputable criterion that can be 

 applied in the separation of closely allied groups, that of 

 sterility or fertility inter se. 



To one who tries to divest himself of the accepted ideas 

 regarding species, and is on the watch for evidence of 

 hybridization among unlike strains that we are accus- 

 tomed to call species, new cases of such hybridization 

 frequently come to light. Especially is this true among 

 the insects. In regions where the faunal areas of two 

 " good " species overlap or are contiguous, such crossing 

 not infrequently occurs. 



A most interesting case is that of the four species of 

 the coccinellid beetle Adalia that occur in the same region 

 in Colorado, as worked out by Palmer. 4 These four forms 

 with clean-cut differences in color and color pattern had 

 been named and described by different authors as dis- 

 tinct species, yet three of them were found to be inter- 

 breeding with complete fertility but still respectively 

 maintaining their identity, forming a regular Mendelian 



* Annals Entom. Soc. America, IV, 3, September, 1911. 



