PART III. 



GENERAL DISCUSSION. 

 VARIATION. 



The variation in the color-pattern of these beetles is so great that the 

 first impression is that it would be useless for taxonomic purposes. Some 

 entomologists have on this ground ventured to say arbitrarily that color 

 differences alone shall be an inadequate specific distinction. While this 

 practice has the warrant that where only a color difference is found, the 

 distinction is generally in fact varietal, such a discrimination against color 

 is of course untenable when the two forms are a distinct unit which do 

 not interbreed. On the other hand, Major Casey considers the color dif- 

 ferences in this family of such taxonomic value that he has created many 

 species thereon which others believe must be ranked as forms or varieties. 



After an acquaintance with these beetles in large numbers, the varia- 

 tions are seen to have very different values. A considerable addition or 

 loss of pigment at some places on the elytra or pronotum will be recog- 

 nized as a mere fluctuation common throughout the range, whereas a very 

 small amount of pigment at another point would show it to be a separate 

 variety or even a distinct species. To the experienced coleopterist this is 

 a commonplace, but the neglect of it by the Wallace- Weismann school of 

 selectionists makes it worthy of note. 



In general, the mere amount of pigment has the least significance. If 

 this pigment is not evenly added to the spots, it becomes more significant. 

 But if it is along the set lines for that species, it is of comparatively slight 

 consequence. It is when it breaks out from the set lines to appear at a 

 different point or to extend in new directions that the systematist may lay 

 stress upon it. 



That the variation is determinate is shown in many ways. By determi- 

 nate variation is here meant a progressive variation in some definite direc- 

 tion, originating within the germ-plasm either with or without external 

 influence, and gradually, by waves or by leaps. The progeny differ in the 

 long run from the parents in some one direction, instead of offering indif- 

 ferently plus( -) and minus ( ) variations in all the old characteristics and 

 having new characteristics in all directions, as seems to be assumed by Wal- 

 lace and in the earlier writings of Weismann. I have not used the term 

 orthogenesis, as I think that it is generally used for determinate evolution 

 operating unswervingly and without divergence in one direction for a long 

 period. Eimer thus used it, contending that the longitudinal pattern steadily 

 and unfailingly develops into a transverse pattern. It is not impossible that 

 such phenomena exist, but the determinate variations here described can 

 not be so characterized. Diversity prevails. Determinate variation will 

 be working in several features at once, advancing now here and now 



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