1 74 % ENTOMOLOGY 



for the fact that these varieties run into one another. One may examine 

 hundreds of potato beetles (L. decemlineatd) 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. 238, and that 

 of Cicindela in Fig. 239. 



Individuals of Cicindela vary in pattern in a few definite directions, 

 and the patterns that characterize the various species 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 (vulgar is, Fig. 239, i) as a central type, the markings of 

 other species vary from that type, (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 (i. e., the individual varia- 

 tions 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 margini- 

 pennis, togata and lemniscata. (4) Those species which vary do so in 

 one direction only." New types of pattern, of specific value, appear 

 to have arisen by the isolation and perpetuation of individual variations. 



Variations in general fall into two classes: continuous (individual 

 variations) and discontinuous mutations. 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. 



R. H. Johnson has published an important statistical study on evo- 

 lution in the color pattern of the lady-beetles. He finds both con- 

 tinuous and discontinuous variations present; that the color pattern is 

 capable of modification by the environment; that some modifications 

 are hereditary characters and others not. 



Replacements. Examples of the replacement of one color by 

 another are familiar to all collectors. The red of Vanessa atalanta and 

 Coccinellidae may be replaced by yellow. These two colors in many 

 butterflies and beetles are due to pigments that are closely related to 

 each other chemically. Thus in the chrysomelid Melasoma lapponica 

 the beetle at emergence is pale but soon becomes yellow with black 

 markings, and after several hours, under the influence of sunlight, the 

 yellow changes to red; the change may be prevented, however, by keep- 

 ing the beetle in the dark. After death, the red fades back through 



