( 451 ) 



a species is really a species ; we work, or ought to work, with the mental reserva- 

 tion that the specific distinctness of our species novae deduced from morphological 

 differences will be corroborated by biology (in the widest sense). The work a 

 systematist has to do is twofold : above all, he is a registrar of facts observed upon 

 the body of individuals, and secondly he has to draw conclusions from those facts. 



All our knowledge of nature is based upon the knowledge of single 

 phenomena. In Isatural History the base of our knowledge is the individual : the 

 characters of individuals and sums of individuals are the ABC of this science ; they 

 are to the naturalist what words are to the philologer. To render the characters 

 clear is the first task to lie solved ; before this task is completed we are not able to 

 draw correct conclusions. Although nowadays the recorder of facts, the diagnos- 

 ticist, does not rank high in science, every theory in Natural History depends 

 especially on the correctness of the facts furnished by the diagnusticist ; when that 

 record lacks correctness the theory based upon it must break down. As an 

 excellent illustration of this we may regard Weismanu's theory * of " Phyletic 

 Parallelism in Metamorphic Species," as far as it asserts the existence of an 

 incongruity in the classification of Lepidoptera based on larval or based on 

 imaginal characters. The " Rhopalocera " are by no means a sharply defined group 

 in the imago state ; neither the erect position of the wing of the resting Ijutterfly and 

 the colour of the wings, nor the clubbed antennae, are characters applying to all 

 '■'■Rhopalocera " and exclusively to Rhopalocera ; and as there is no single character 

 by which all the Rhopalocera are distinguished from all other Lepidoptera, we can 

 also not expect that the larvae of Rhopalocera form a sharply defined group 

 distinguished as a whole from all other Lepidopterons larvae. The apparent 

 incongruity in the classification according to the larval or imaginal state of 

 " Bomhycidae " and " Xotodontidae " again is not due to an incongruent development 

 of larvae and imagines, but to the fact that Lepidopterists have placed in these 

 (and other) families the most heterogeneous things in consequence of an entirely 

 inadequate knowledge of the forms classified. 



We learn from this illustration first that diagnostic work is the true basis of 

 evolutionistic theories and hence of the highest importance, and secondly that the 

 record of facts must be exact. Huxley says that the record of facts is not scientific 

 if the facts do not permit of the drawing of general conclusions. In the above case 

 the blame is much more on the side of the systematists who gave the clubbed 

 antennae as distinguishing character of butterflies, than on the side of Weismann 

 who accepted this statement as correct. If, therefore, diagnostic work is intended 

 to meet the claim of furnishing facts from which general conclusions as to evolution 

 (classification, variation, etc.) can safely be drawn, or if a diagnosticist claims to 

 have his work regarded as scientific, it mnst be well distinguished lietween the 

 description of the characters of individuals and the statement of an oi)iuion deduced 

 by the diagnosticist from the characters of the individuals ; the record of the 

 characters of individuals, or the statement of facts, ought to precede the statement 

 of the personal conclusion, which perhaps is entirely wrong. In the case of species 

 and lower degrees of divergency diagnosticists mostly lose sight of this ; when we 

 describe a number of individuals as belonging to a new species we present very often 

 to the reader, not the characters of the specimens, but a ready-made conclusinn which 

 asserts (1) that the specimens are sjiecifically identical, and (2) tliat the species 

 varies in colour, markings, structure, and si/.e to such and sucli an extent. The specific 

 Weismann, Studies in tlir 'flicorij of DesfiiU, London, 1S82. II. p. 4:t2. 



