194 The Mechanism of Evolution in Leptinotaksa 



The first De Vries considers as due in the main to the conditions of nutrition 

 or an amphimixis-like process, the second to processes at present unknown but 

 having no relation to the first. If the proposition of De Vries is true, then the 

 ordinary or the common intergrading differences of our " simplest characters " 

 ought to be all in line, and this would also be true if Weismann's proposition is 

 true, the chief point of difference being the part these might play in the evolu- 

 tion of organisms. 



The first three " simplest characters " for examination, c, l, and d, are deposits 

 of pigments at invariable positions on this portion of the body; they are end- 

 products and as such are the visible manifestation of a specific property of the 

 entire mass in the same way as the angles in the faces of a crystal are specific 

 properties. Spots c, b, and d have position, dimensions, area, volume, and as a 

 consequence of position sustain exact relations to adjacent parts and characters 

 and present within themselves something of internal organization. 



Fig. 13. — Showing variation in shape of spot c as it occurs in L. undecimlineata. 

 The figures represent examples chosen from many thousands of individuals taken 

 In successive years over an entire known range of species, but show diversity in 

 shape as well as in size that this area may present in this species. 



In L. undecimlineata, spot c is sometimes absent, as in figure 13a, but in the 

 great majority of individuals it is present, ranging from the conditions of a min- 

 ute spot (figure 136) to even larger areas than are shown in figure 13d. In 

 any and all individuals the spot is present or absent as a unit, and never breaks 

 up into lesser centers of color deposition. A careful examination of the spots 

 found on the pronota of this species at the center (c) shows that they are not 

 all of the same shape, any more than they are of the same size. The difference 

 in size, as far as it is expressed in area exposed, may be a purely quantitative 

 matter, but the shape of the spot is quite another matter. Is this difference in 

 shape quantitative or qualitative ? 



The simplest condition in which this spot appears is in the form of a small 

 round area of pigment (fig. 13&,) and from this as a center the spot pushes out 

 first in one direction, then in another, sometimes in two opposite directions 

 (figures 13/ and 13h), to produce an oblong spot; at other times it pushes for- 

 ward and outward (fig. 13^) and medianward at the same time, or it may push 

 out in four directions, as in figure 13y. It is not uncommon for the spot to grow 

 larger without development in any one direction, simply adding pigment equally 

 on all sides, as in figure 13d. It must be fully comprehended that these direc- 

 tions in which the spot extends are not in the least purely chance directions, but 

 are firmly fixed in position, delimited in some manner in the physical constitu- 

 tion of the matter involved. 



