66 DARWINISM TO-DAY. 



exists. On the other hand, in the honey-bee the bilateral correla- 

 tion of variation seems surprisingly small (see pp. 214-222). In 

 the case of variations in pattern, also, there is no uniformity among 

 the various cases studied. In Hippodamia convergent (p. 257 et 

 seq.) the two elytra show pattern-variations quite independently; 

 in Diabrotica soror (p. 274 et seq.), on the contrary, there seems 

 to be a marked right and left correlation in the elytral pattern- 

 variation. In the cases of the variation in number of tibial spines 

 on the right and left hind tibiae of locusts (p. 301) and cicadas (p. 

 306), we have simply made a brief statement, in each case, of the 

 actual conditions of correlation, leaving the reader to draw his own 

 conclusions. In the case of the variation in actual and relative 

 length of the antennal segments of the scale insect, Ceroputo yucca 

 (?) (p. 310), there is a surprising lack of correlation between the 

 right and left antennae. 



"We have not attempted to determine the mathematical expression 

 (coefficient of correlation) for any of the cases studied. The data 

 presented, however, will enable any biometrician, who sees an 

 advantage in doing this, to do it. But without checking our results 

 by the use of that method there seems, on the whole, to be a sur- 

 prising lack of that fine degree of correlation in variation which 

 we should expect to find existing, if we believe that the actual 

 existing conditions of structure and pattern in these bilaterally sym- 

 metrical animals are an expression of the result of the action of 

 a rigorous natural selection. If one condition of pattern or structure 

 is the most advantageous (of the many conditions which selection 

 among a host of fluctuating variations could have established), 

 surely this condition ought to be pretty closely similar on both sides 

 of the insect. That as much bilateral variety as actually exists, 

 in many of the species examined by us, should exist a variety 

 comparable in certain cases even with the degree of variety revealed 

 by the comparison of considerable series of individuals is a state of 

 affairs that only confirms us in the belief that these innumerable 

 small continuous variations, on which for so long the thorough- 

 going selectionists have put their faith as the sufficient bases for 

 natural selection's species-forming work, are clearly not competent 

 to serve as such bases. If these 'continuous' variations are the foun- 

 dation stones of new species, some other agents than selection must 

 be found or invoked to build several courses on them, to produce 

 some cumulation of them, before natural selection finds them of 

 that life-and-death worth which is the prerequisite for her potent 

 interference." 



21 Henslow, the botanist, has maintained a constant attitude of 

 antagonism to natural selection on the basis of his belief that the 



