214 ENTOMOLOGY 



far more variable than others. Catocala ilia, for example, 

 occurs under more than fifty varieties, each of which might 

 be given a distinctive name, were it not for the fact that these 

 varieties run into one another. One may examine hundreds 

 of potato beetles (L. decemlineata) without finding any two 

 that have precisely the same pattern on the pronotum. The 

 range of this variation in this species is partially indicated in 

 Fig. 237, and that of Cicindela in Fig. 238. 



Individuals of Cicindela vary in pattern in a few definite 

 directions, and the patterns that characterize the various spe- 

 cies appear to be fixations of individual variations. In the 

 words of Dr. Horn: " (i) The type of marking is the same 

 in all our species. {(2) Assuming a well-marked species (vul- 

 garis, Fig. 238, i) as a central type, the markings of other 

 species vary from that type, (a) by a progressive spreading 

 of the white, (&) 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 (i. e., the individual variations are small in amount 

 as compared with those in other species). These fall into 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 

 niarginipennis } togata and lemniscata. (4) Those species 

 which vary do so in one direction only." New types of pat- 

 tern, of specific value, appear to have arisen by the isolation 

 and perpetuation of individual variations. 



Variations in general fall into two classes : continuous (in- 

 dividual variations) and discontinuous (sports). The former 

 are always present, are slight in extent and intergrade with 

 one another; they are distributed symmetrically about a mean 

 condition. The latter are occasional, of considerable extent 

 and sharply separated from the normal condition. 



Replacements. Examples of the replacement of one color 

 by another are familiar to all collectors. The red of Vanessa 

 atalanta and Coccinellidse may be replaced by yellow. These 



