39 



form gets specialized in very different directions and in so doing 

 gives rise to numerous new forms, one group acquiring this, an- 

 other group that improvement. 



In a case like this, that organ is the most primitive which does 

 not show any new modifications, hence has preserved the charac- 

 teristics which they have all in common in the pure forms, but 

 certainly not such an organ, as we might artificially compose by 

 summarizing all the new formations. 



It is my opinion that this way of looking at the question can 

 be justified equally well, and that it is certainly oftener used in 

 comparative anatomy than the method of Fracker, of which he 

 asserts that it is the ordinary one in problems of this kind (1. c. p. 17). 



Fracker tries to give a solid basis to this summarizing hypo- 

 thesis by the description of the prothorax of Hepialus lupulinus. 

 In the first place the drawing on which this description has been 

 founded is not Fracker's but Dtar's work. And though I have 

 a great respect for the exactness with which this writer generally 

 works, it still remains exceedingly dangerous to take another 

 man's drawing like this, as the chief basis of a hypothesis which 

 upsets all former ideas. This, however, is not the greatest ob- 

 jection which I have to Fracker's opinions. The point I am 

 going to treat now is of a more general nature. 



I think that it is not quite scientific to raise one segment, 

 picked out at random in an arbitrarily chosen family, to the rank 

 of the most generalized type. Such a procedure could only be 

 justified by adducing a number of facts to prove that all or at least 

 nearly all the members of the family possess the same foundation. 

 This is not at all the case here and Quail's descriptions of the Hepia- 

 lidae (1900) might have taught Fracker (1915) as much. Though 

 the family of the Hepialidae is justly considered to be a primitive 

 one, this does not include the necessity that all the features of 

 all the members have to show a primitive character and that they 

 cannot possibly have undergone any secondary modifications. A 

 study of the existing literature would have taught Fracker that 

 in 1914 and 1915 (and in 1916), J. F. van Bemmelen found 



