26 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



No. I of the accompanying plate (Fig. i) is the under- 

 lying pattern from which all the forms observed in our 

 Cicindela have been derived. 



"Before going further it is vi?ell to present the fol- 

 lowing propositions that the argument ard the illus- 

 trations may be understood. 



"I. The type of marking is the same in all our spe- 

 cies. 



"2. Assuming a well-marked species as a central 

 type the markings vary, 



a, by a progressive spreading of the white, 



b, by a gradual thinning or absorption of the white, 



c, by a fragmentation of the markings, 



d, by linear supplementary extension. 



"3. Many species are practically invariable. These 

 fall in two series, 



a, those of the normal type, as vulgaris, hirticollis, 

 and tenuisignata, 



b, those in which some modification of the ,type 

 has become permanent, probably through isolation, as 

 marginipennis, iogata, and iemniscata. 



"4. Those species which vary, do so in one direc- 

 tion only. That is, supposing a species begins typ- 

 ically with markings similar to vulgaris, the variation 

 may be either in the direction of thickening and in- 

 crease of white, as in hyperborea, generosa, and others, 

 or in the direction of thinning or fragmentation of the 

 white with perhaps an entire loss of markings as in 

 hemorrhagica, splendida, or obsoleta. 



"The first two propositions must be considered as 

 applying to the species of the genus collectivel)', the 

 last two to the species separately. 



"The accompanying plate has been prepared to 

 illustrate these propositions. It must, however, be 



