3IO 



KELLOGG AND BELL 



Variation in Actual and Relative Length of Segments of 

 the Antennae of Ceroputo yuccas (?) (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 Coccid^ 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 



5Classes' 2 

 {Variat es 2 



Fig. 77. Frequency polvgon of 

 the variation in number of spines in 

 inner row of right tibiae of 48 female 

 seventeen-year cicadas, Cicada sep- 

 iefidecim ^ mean, 3.52 ; index of vari- 

 ability, .67 ; coefficient of variation 

 I9-3- 



3£iii4taL;jS|. 



Fig. 78. Frequency polygon of 

 the variation in number of spines in 

 inner row of left tibite of 47 female 

 seventeen-year cicadas, Cicada sep- 

 tettdecim ; 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- 

 ■piito and 34 species of PhenacoccuSy a closely allied genus, to 

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

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



