154 PHILOSOPHY OF ZObLOGY. 



LINNJJUS was disposed to restrict his specific characters 

 to twelve words, an example which succeeding naturalists 

 have usually imitated. In general, however, all that is ne- 

 cessary to be included in a specific character, particularly 

 where all the species which are known are accessible to 

 our inspection, may be expressed, even within the limits of 

 the Linnaean rule. Where the characters of a species are 

 subject to variation, from sex, age, or season, it is of im- 

 portance to employ those marks only which are permanent, 

 and common to all the individuals. 



Specific characters necessarily vary with the addition of 

 new species. If a genus consists of two species, the one 

 constantly black, and the other white, the colour will fur- 

 nish the marks for the specific character. Should a third 

 species be discovered likewise of a black colour, it will not 

 only be necessary to frame a specific character for the third 

 species, but to reconstruct a new one for the first. 



3. Specific References. It is usual to add, immediately 

 after the specific character, a reference to those works in 

 which the species has been described, under whatever name, 

 and to arrange the whole in the order of time. It does not 

 appear to be worth while to quote those authors who have 

 not contributed any thing towards the elucidation of the spe- 

 cies, but who have merely copied from others, unless in 

 the case of those systematical works which are generally 

 consulted. When references are made without selection, 

 much room is unprofitably occupied. 



4. Specific Description. This includes every circum- 

 stance in the history of the species, not previously recorded 

 in the characters of the groups in which it is included. 

 The mature male, during the season of love, is described 

 as the standard of the species, with which all the differences 

 arising from sex, age, or season, are compared. 



