4 EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



The differences in sculpture of the elytra have not been found to have 

 the constancy and systematic value which some of the earlier writers 

 have placed upon them. The variation is, moreover, largely ontogenetic, 

 as I have observed in the pedigreed material. The shape of the elytra 

 must also be used with considerable caution, because of its variability, as 

 shown in table 2, and the optical illusions from the angle at which they 

 harden and from the longitudinality or the reverse of the pattern. 



The sex of the individuals has in most cases been observed ; always in 

 the experiments. The same sex is not the more heavily pigmented in 

 every species. The sexes are not given separately except where the 

 difference was obviously significant. The color-patterns of the larvae have 

 been used in evaluating relationships in some cases, but their description 

 is outside the field of this paper. 



The numbering of the elytral spots employed in Hippodamia convergens 

 follows Weise, not Kellogg and Bell (see figs. 3, 6, and 17) . In other genera 

 a corresponding system is employed: + is used to indicate confluence, ap to 

 indicate a close approach to confluence, si-}- for a very slight confluence, 

 and tr for transition between separateness and confluence. 



Formulae are used where possible to designate unnamed varieties; in 

 other cases it has been necessary to use letters. New names have been 

 given to varieties only when they are common, distinct, and frequently 

 collected, so that a name is needed. 



PRINCIPLES OF CLASSIFICATION. 



There is an improper demand for finality of treatment on the part of 

 many systematists. These workers wish to use a treatise almost solely for 

 the purpose of definitely dividing their collected specimens into categories. 

 Such a demand leads many systematic writers to a false positiveness in 

 regard to distinctions and evaluations. Many revisions are thus led to 

 present a precision and show of finality which is not justified. New names 

 involving new distinctions are valuable, but the reviser who fails to bring 

 to light the points of doubt and uncertainty as well is negligent. A revi- 

 sion should give questions as well as answers; it should not only shed 

 light, but indicate where more light is needed. To assume surety on an 

 inadequate basis is inimical to the advance of science. On the other hand, 

 there are some who go to the other extreme and hesitate about calling 

 attention to an apparently new species, or some other difference, until they 

 feel wholly assured. This policy retards progress and may result in the 

 information never being made public because of the intervening death, 

 incapacity, or disinclination of the investigator. An impression based 

 upon extensive special knowledge has scientific value, provided it is avow- 

 edly only an impression. I have not sought, therefore, in this revision any 

 degree of finality, but have tried to adopt a nomenclature which, from 



