No. 570] TAXONOMY AND EVOLUTION. 



379 



the embryologist and morphologist are engaged upon their own 

 special tasks. 



The Comparative Value of Internal and External Parts 

 Briefly reviewing the discussion as far as we have carried it, 

 it will be seen that we are asking for sound phylogeiietie. classi- 

 fication of the smaller groups as well as of the larger ones, based 

 not upon single characters, hut upon the whole of the characters 

 regarded collectively, for more careful and more thorough mor- 

 phological methods in description and for the discontinuation 

 of the provisional diagnosis. In view of the desirability of work- 

 ing up sounder schemes of classification from the enormous, un- 

 wieldy and superficially known mass of genera and species sys- 

 tematists can he rendering little service by continuing to turn 

 out indiscriminate provisional diagnoses. 



It remains now to discuss in greater detail the proposal we 

 bring forward in the place of the provisional diagnosis. 



The commonly accepted opinion is that while for the classifi- 

 cation of families and orders the internal parts must be taken 

 into consideration, for that of species and genera a summary of 

 the external parts is all that is required. On account of the 

 labor and difficulty sometimes involved in dissection we are too 



present a dismal monotomy of character which it would be 

 profitless to investigate for systematic purposes. 



If it is admitted that internal characters are of value among 

 the higher divisions of the animal kingdom, can the systematist 

 tell us at what precise point in the downward scale they cease to 

 have value, and at which reference need only be made to the 

 external parts? Even supposing for a moment that there is 

 such a limit, we are strongly of opinion that it does not come 

 before the genera. 



A genus is of different value in different groups but as a rule 

 it presents so much difference in external form from other 

 genera as to warrant the inference that internal differences of a 

 like extent will be found if sought for. At the present moment 

 a genus is a perfectly arbitrary collection of species. We ven- 



generic relationships will he more carefully defined and genera 



hy the way. 



