3 io 



KELLOGG AND BELL 



Variation in Actual and Relative Length of Segments of 

 the Antennae of Ceroputo yuccae (?) (a Scale Insect). In the 

 systematic study of the Coccidae (scale insects) the actual and 

 relative length of the various segments composing the antennae 

 are often used as specific characters. The Coccidae are insects 

 with incomplete metamorphosis, and the larval and adult anten- 

 nae are identical structures showing however some develop- 

 mental change ; in many Coccidae there is one segment fewer in 





FIG. 77. Frequency polygon of 

 the variation in number of spines in 

 inner row of right tibiae of 48 female 

 seventeen-year cicadas, Cicada sep- 

 tendecim j mean, 3.52; index of vari- 

 ability, .67 ; coefficient of variation 



FIG. 78. Frequency polygon of 

 the variation in number of spines in 

 inner row of left tibiae of 47 female 

 seventeen-year cicadas, Cicada sep- 

 tendecimj mean, 3.62; index of vari- 

 ability, .67; coefficient of variation 

 18.5- 



the antennae during larval life. The relative lengths are indi- 

 cated by a formula composed of the ordinal numbers of the 

 segments (segment one being the basal one) (fig. 79) arranged 

 in linear series beginning with the number of the longest seg- 

 ment followed by the number of the next to longest and so on. 

 There are at present known six North American species of Cero- 

 puto and 34 species of Phenacoccus^ a closely allied genus, to 

 which most of the Ceroputo species were first ascribed, and in 

 the specific diagnoses of nearly all, the " antennal formula " is 



