3l6 APPENDIX A. 



has not discriminated between the natural genus (i.e. the genus as 

 evolved by the laws of Nature) and the human conception of 

 a natural genus ; the former of course has no type, but the latter 

 is founded on one or more species, and these we call its types or 

 exponents (not the exponents of the genus, but the exponents of 

 the definition of the genus). 



In ordinary life we talk of 'yards' or 'metres,' knowing well 

 what we mean and what w411 be understood by these terms, and 

 we buy and use representations of these measures, but even in such 

 cases the 'type' is a necessity well understood by Governments 

 who carefully preserve for reference the original standard or ' type ' 

 of each unit. In like manner zoologists recognise the necessity 

 for having a standard of reference for each named conception, by 

 which one person can carefully test and understand what another 

 person means. Thus has arisen the system of types, without which 

 all zoological work must be merely chaotic, for zoologists have not 

 been infallible in the past, nor will they be in the future. 



There is still another aspect to this question : we assume that 

 we have established zoological conceptions which will endure, but 

 a hundred years hence these conceptions may be proved to be 

 utterly erroneous, and our isotypical genera may be found to be as 

 heterotypical as we now deem those of Hubner's VerzeicJiniss 

 to be. Then the only method by which the names of the present 

 century will be capable of employment and of comprehension will 

 be the adoption of our cited types carrying with them our generic 

 names, to which may perhaps be applied definitions founded on 

 characters of which at present we have no conception. When the 

 time shall have arrived in which all genera shall have been rendered 

 isotypical, and when no zoologist will be capable of committing 

 the error of publishing a heterotypical genus, then and then only 

 can we ignore " le systeme de types generiques,' but until that day 

 shall dawn we must, as in the past, rely upon the type-system, in 

 the principles of which practically all concur, difference of opinion 

 being only noticed in matters of detail as to the method of fixing 

 the type." 



87. KiRBY (W. F.). 20 July 1897. 



[Vide Kirby 77. Durrani.^ 



" VII. 2, 2 A ; VII. 3 ; VII. 6 A. I agree with these propositions." 



[i.e. VII. § 2. That the type must conform to the original description 

 of the genus, &c. 2 A. Unless direct error of observation can be inferred. 



§ 3. That a species included with doubt cannot be the type. 



§ 6, Subsequent citation or restrictions must be accepted in chrono- 

 logical sequence : 



6 A. If they are not at variance with the original intention of the 

 author. Durrmit.'] 



