98 



EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES- 



various degrees, the categories used in the table are of course not sharply 

 limited, but merely arbitrary points taken for exemplification. 



There can be no one general orthogenetic influence here, so diverse are 

 the many varieties which have arisen from Hippodamia convergens in dif- 

 ferent regions. Eimer's law, that a primitive pattern of stripe is followed 

 by spots, which in turn give way to tranverse striping, and last of all to 

 a uniform color without spots or stripes, can not hold. In fig. 90 the vari- 

 eties of Hippodamia convergens are so arranged as to show how one degree 

 of one line of development may be combined with another degree of another 

 line of development. In fig. 29, in Hippodamia spuria, a similar condition 

 is met with, even though here we deal with both stripe and bars. Another 

 law of Eimer's, "new markings appear upon the body of an animal from 

 behind forwards and above downwards, or conversely, whilst the old ones 

 disappear in the same direction and succession, " is also untenable. The 

 study made of the order of disappearance of spots does not bear out this 

 rule, nor does the appearance of new spots, such as q and e in Hippodamia 

 convergens, conform to it. The diversity of patterns here makes impossible 

 the formulation of any general orthogenetic law, for, as we have seen, 

 they progress differently from place to place. In fact, the general diver- 

 sity of the animal kingdom throws great doubt on all general laws of 

 orthogenesis. The doctrine of determinate variation is only handicapped 

 by the formulation of these rules, which must be so soon abandoned. 

 Determinate variation is as multifarious as are the phenomena it aims to 

 explain. 



TABLE 21. Effects of cooperation or of opposition of some evolutionary factors 

 upon a new characteristic. 



Evolution may conceivably proceed in a regular and continuous fashion, 

 and it has been generally so conceived, until of recent years, when much 

 attention has been paid to the evolution by leaps. Considerable evidence, 

 as to positions of organic stability and unit-characters, is held to substan- 

 tiate this view. In these beetles we would seem to have both saltatory 

 evolution in a character like 1 + 3 in Hippodamia convergens and evolu- 



