" Permit me, my son, to tell you what is knowledge. What you are 

 acquainted with, consider that you know it; what you do not under- 

 stand, consider that you do not know it; this is knowledge." 



Dr. Hagen has incorrectly given the history of Eurytheme. 

 On page 151 we are told: " The breeding of Eurytheme and its related 

 forms, by the late J. Boll, in Dallas, Texas, has been the first step to a 

 better knowledge, and to a scientific reduction of the species of Colias. 

 Mr. Boll had raised Eurytheme through two years, 1874 and 1875, and 

 had sent, in the summer of 1876, his paper, accompanied with numer- 

 ous specimens, to Hamburg. This paper was read at the meeting of 

 the Assn. of Naturalists, Sept. 20, and printed directly in the Tagblatt, 

 etc. The excellent paper by Mr. Edwards, N. A. But., Vol. 2, was 

 the result of similar experiments by N. Am. Lepidoterologists. 



On page 168, under Philodice, after reproaching me for disagreeing 

 with his views about the *' numerous doctrines of the present paper," 

 which he had informed me of in a letter, the Doctor proceeds: 

 " apparently he has forgotten that he persistently separated Eurytheme 

 Keewaydin and Ariadne as different species, till the late Mr. Boll 

 proved that all three belonged to the same species." 



I will here take the opportunity to say, with reference to this obsti- 

 nate trait with which the Doctor reproaches me, that I work, and have 

 for 20 years worked, on a consistent plan. T. may be different from 

 that of other persons, but it leads to good results. If, in my opinion 

 — not another man's — a form of butterfly, of which nothing is known 

 except by the dried specimens, is distinct enough to deserve a specific 

 name, or I may say, in the words of Prof. Richard Owen, " the differ- 

 ences on which the specific character are founded, are constant in in- 

 dividuals of both sexes, so far as observation has reached," I give the 

 name without hesitation. I do not relegate such a form to one of its 

 next allies as a mere variety of it, for the reason that neithei* I nor any 

 one can tell anything about it except what the dried example itself 

 shows. It has several times happened, after further materials have 

 come in, that I have seen occasion to change my views, and I am not 

 at all unready to change when I see reason. But in many other cases 

 it has turned out that the forms which I have designated as specific are 

 but polymorphic seasonal forms of one species, as in the case of Eury- 

 theme. In such a case, at least, I have been right in naming such 

 forms as distinct species, even if I might guess at the possible connec- 

 tion between them. Till breeding from the ^gg should establish the 

 connection, a connection could not safely be asserted. Conjecture 

 based on field observation only cannot be tantamount to actual proof. 

 We have an element of uncertainty always, and I want certainty. My 

 motto is, " indefinite knowledge is definite ignorance." What business 

 had I to put Ariadne with Eurytheme from any knowledge we had of 

 these two forms! Usually such polymorphic forms are fully as distinct 

 from each other as many species which have never been doubted, 

 as, for example, the two forms of Grapta Comma. In the case of 

 AJax with its 3 forms; Boisduval, a first-rate lepidopterist, named one 

 of them Marcellics, as a distinct species; Felder, another first-rate 

 authority, named another of these forms Telafnonides, and before 



