STUDIES OF VARIATION IN INSECTS 257 



the mode being 1.2 mm., the mean 1.16 mm., the standard 

 deviation .7 mm. and the coefficient of variation 6.03. 



Thus in these short series the females show a slightly greater 

 variability, in respect to this character, than the males. With 

 the difference in variability so small, and with such short series, 

 it is obvious that no generalization of worth can be made con- 

 cerning the relative degree of variability in males and females. 

 We are now attempting, however, to obtain lots of mosquitoes, 

 each lot to be composed of individuals of one brood, and bred 

 under identical environment so as to exclude, if possible, all but 

 innate differences between the males and females. In these 

 bred lots we shall examine quantitatively a number of varying 

 characters of structures and pattern. 



Variation of the Pattern of Hippodamia convergens (the Con- 

 vergent Lady Bird). The " lady-birds" are small, brightly and 

 sharply marked beetles which often occur in large numbers, es- 

 pecially where their food, the soft-bodied plant-lice and young 

 scale insects, abounds. In California these beneficial little 

 beetles are abundant, the species Hippodamta convergens being 

 one of the most familiar and numerous. This species, like some 

 others, has the curious habit of assembling in winter time often 

 in enormous numbers in a single mass or in several adjacent 

 masses, in the axils of palm trees, in holes in stumps, or under 

 leaves on the ground. About 40,000 individuals were collected 

 on November 5, 1901, from such a hibernating assembly under 

 leaves at the foot of an oak tree in the Sierra Morena Moun- 

 tains, near Stanford University. All these individuals were 

 inside of a circle twelve feet in diameter. Many more thousand 

 specimens could have been taken from the same circle. 



A series of individuals taken at random from this lot was 

 examined and arranged on the basis of the variation in the 

 character and number of the small but distinct black spots on 

 the dorsal aspect of the red-brown elytra. The lady-birds have 

 a complete metamorphosis, and the color pattern of the adults 

 (imagines) appears in definitive and unchangeable form immedi- 

 ately (after the expanding and drying of the wings, legs and 

 body-wall) on the issuance of the imago from the pupal cuticle. 

 This color pattern is to be looked on as a strictly congenital 



