ON VARIATION. 25 



from the liquid to the solid state. I have stated the 

 case in the following language : l 



"As one or more periods in the life of every spe- 

 cies is characterized by a greater rapidity of develop- 

 ment " (ontogenetic) " than the remainder ; so in pro- 

 portion to the approximation of such a period to the 

 epoch of maturity or reproduction is the offspring 

 liable to variation. During the periods corresponding 

 to those between the rapid metamorphoses, the char- 

 acters of the genus would be preserved unaltered, 

 though the period of change would be ever approach- 

 ing. Hence the transformation of genera may have 

 been rapid and abrupt, and the intervening periods of 

 persistency very long. Thus, while change is really 

 progressing, the external features remain unchanged 

 at other than those points, which may be called ex- 

 pression points. Now the expression point of a new gen- 

 eric type is reached when its appearance in the adult 

 falls so far prior to the period of reproduction as to 

 transmit it to the offspring and their descendants." 



i. VARIATIONS OF SPECIFIC CHARACTERS. 

 a. Variations in the Coleopterous Genus Cicindcla. 



Dr. George H. Horn has trkced the variations in 

 the color patterns of the elytra of the North American 

 species of this abundant and well-known genus. He 

 shows that they form series, in the following language : 2 



"Any one in glancing over this series will perceive 

 that there is a great similarity of marking between 

 many species. This similarity, which may be con- 

 sidered as the type of marking, and is illustrated by 



1 Origin of the Fittest, p. 79. 



2 Entomological News, Philadelphia, Feb., 1892, p. 25. 



