6 ILLINOIS BIOLOGICAL MONOGRAPHS [400 



ditions. It will be shown that biogenetic law must be applied with, 

 caution and is not of such broad application as is held iu some quar- 

 ters, being inapplicable to various characters altogether. 



The brilliant colors of the group are due to physical phenomena 

 determined by Professor Llichelson, and leave no place for the bioge- 

 netic law iu connection with the development of color during ontogeuj'. 

 It will be shown further that color is closely correlated with general 

 physiological condition and is modifiable by conditions which affect 

 general metabolism. The results here pi'esented are based on several 

 years of observation. 



In 1903 the writer undertook a study of, variation of the tiger 

 beetles. The work here presented is the outgrowth of this beginning, 

 and indeed includes some small portions regarding color patterns that 

 were written in that year. The work has been prolonged for many 

 reasons, but chief of these was the' very large number of species in 

 the group and the fact that an adequate understanding of the mate- 

 rial could not be attained without consulting many large collections. 

 Further, the experimental results obtained in 1906 demanded a first- 

 hand study of the variations of the species concerned and their natu- 

 ral habitats. The accumulation of material and data was not com- 

 pleted until 1911. Some of this had to be studied, drawings made, etc., 

 which with numerous other duties and enterprises iiuder way made 

 necessary much time to put it into the present form. 



A family with i^pwards of 1300 species of which more than 600 

 are in one genus and with characters which can be studied and 

 analyzed, appeared to afford material which was sufficiently promis- 

 ing to justify delay. In the fourteen years that have elapsed since 

 the problem was first undertaken at the suggestion of Dr. C. B. Dav- 

 enport, the attention of biologists has shifted from variation, which 

 was then the chief topic of interest, to experimental modification of 

 characters, and finally to the methods of modern genetics. Various 

 men have made numerous suggestions regarding the work, but in its 

 final preparation the writer has been able to use only a few of them 

 in a general way, and an attempt is made to present tlie facts and 

 conclusions growing out of the material as simply as possible. 



MATERI.\LS AND METHODS 



The material which has been used as the basis of this work has 

 consisted of collections in the family Cicindelidae of the world, exten- 

 sive collections of several North American species, repeated year-to-year 

 collections of a few species in Illinois and Indiana, series of observations 

 on the ontogenv of color in a small number of North American species. 



