44 TYPES OF MENDELIAN HEREDITY 
like the age of the individual, also be considered as 
influences external to the hereditary factors which 
affect the development of characters. And not only 
c 
Fig. 20.—Leptinotarsa signaticollis (above), and L. undecimlineata 
(below), with their full grown (B) and second stage (C) larve to the right 
of each. (After Tower.) 
do regional peculiarities influence characters, but 
special regions are usually required for a given factor 
difference to manifest itself, just as certain tempera- 
tures or ages may be necessary. Thus when we 
