204 KELLOGG AND BELL 



Variation in number of metathoracic tactile hairs of Lipeurus celer and 

 L. varius (biting bird-lice) ..'..' ... . . 313 



Variation in arrangement of elytral striae of Pterostichus sp. (predaceous 

 ground beetle). . .' . . . % -> .'..;'.. .'-.'.-'. : \. '.' . . .... 316 



General Results and Significance. 



Congenital (blastogenic) and acquired variation . . 319 



Continuous and discontinuous variation. . . :; r ,-. ... 321 



Rigor of natural selection and determinate variation .... . , 324 



Variation in parthenogenetically produced individuals, and in those of bi- 

 sexual parentage. ... . . . . . 329 



Variation in males and females ..... ... .... 330 



Correlated variation ; bilateral symmetry, metemerism, and other corre- 

 lations 330 



THIS paper presents the results of certain qualitative and 

 quantitative (statistical) studies of variation in a score of in- 

 sect species. The individuals composing the various lots or 

 series examined were taken from their natural habitat and noth- 

 ing is known of the particular ancestry of any of them (except 

 in the case of the bees). Nor is the environment (conditions of 

 life) known more exactly than is commonly known of insects 

 taken under such natural conditions. 1 The writers present 

 quantitatively determined data which relate to (a) the distinction 

 between congenital and acquired variation ; (b) the distinction 

 between continuous and discontinuous variation ; (c) the exist- 

 ence of determinate variation ; (d) tests of the rigor of natural 

 selection ; (e) the extent of congenital variation in parthenoge- 

 netically produced individuals compared with that in individuals 

 of the same species, of bi-sexual parentage ; (f) the extent of 

 variation in males as compared with that in females of the same 

 species ; (g) correlated variation, especially in cases of bilateral 

 symmetry and of metemerism ; and (h) the significance of 

 variation in the systematic study of insects. The paper is cast 

 in such form that the specific data, tabulated and plotted, of the 

 variations found in the various insect species studied follow a 

 brief introductory part which refers to what seem to the writers 

 the particular availability and worth of insects as subjects of 



1 For an account of variations in a single insect species among individuals of 

 known ancestry and of known and experimentally controlled varying conditions 

 of nutrition, see Kellogg and Bell, "Variations induced in larval, pupal and 

 imaginal stages of Bombyx mori by controlled varying food supply," Science, V, 

 18, N. S., pp. 741-748, December, 1903. 



