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seen, are indeed highly susceptible to it, whereby, immediately a species begins 

 to differentiate, the organs usually also speedily begin to change. But where, 

 then, is the boundary between the old species and the new? This can only 

 be fixed, when the change has gone further, and as the differentiation of the 

 genitals goes on independently and therefore does not necessarily keep pace 

 with that of the other organs, it is quite possible, that in two forms, which in 

 other respects have come to differ so much from eachother that they must 

 obviously be regarded as different species, the genitals may be still unchanged, 

 and thus be the same in both forms. The evolutionary character of these changes 

 in the genitals has been very clearly shown by the latest researches. Of a series 

 of Pieridae to which the Pieris Judith F. of Java belongs, closely related forms 

 are found in various other districts of the Indo-Malayan fauna, forms, which, differing 

 sufficiently in colour and markings to be systematically divisible into different species, 

 are yet mutually closely related, and form, as it were, a series of species flowing 

 into one another, apparently all differentiated out of the same original stock. 

 The research in question showed, that in all these forms the genitals differ 

 from one another, but so slightly and in such a way, that these organs also 

 show exactly the same gradual transition, and thereby demonstrate, that they 

 too have come, through evolution, from the same original stock form. But does 

 this justify us in forcing the systematist to ackwowledge them as all belonging 

 to one species ? How would it have been, if only the most differentiated forms 

 had been preserved? It is one-sided to attach so great a systematic importance 

 to a single organ. We have to recognize the fact, that it is not the animal as 

 such but every organ, each physiological unit, which develops evolutionary changes, 

 independently, sometimes but not always simultaneously with the others and in 

 connection with them. 



It was with great satisfaction that I saw, that an opinion in support of 

 mine had been expressed by an authority a short time ago. In the Entonio- 

 logische Rundschau for June 19 15 there is a short review by Dr. Ad. Seitz, 

 in which he says that, although the genitals of the Lepidoptera are certainly 

 useful in recognizing the different species, it is an error to expect to find 

 rigid specific characteristics in them, and even to attach more value to them 

 than to what can be learned in this respect from the study of the primal 

 conditions, which alone can give certainty on the subject. He quotes as an example 

 that the excessive difference in the form of the male genitals in the American 

 Erycinidae makes them absolutely useless for the above purpose, and that, if 

 such differences were really of specific significance, Papilio Xurnas for instance 

 would be a different species to Papilio Xuthulus, which is really nothing but 

 a springtime generation of the first. What he here calls,— in accordance with 



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