The Origin of the Markings of Caterpillars. 359 



Four parallel series here proceed from the 

 parent-form Hippophaes ; there may have been 

 five, or possibly only three, but the incomplete 

 state of our knowledge of the ontogeny does not 

 permit of any certain conclusion. For the point 

 under consideration this is, however, quite imma- 

 terial. The distance from the central point (the 

 parent-form) indicates the grade of phyletic de- 

 velopment which the respective species have at 

 present reached. 



There is another case which is no less instruc- 

 tive, because it reveals, although in a somewhat 

 different manner, the action of a law of growth 

 innate in the organism itself, but which can never- 

 theless by no means be regarded as equivalent to 

 a phyletic vital force. I refer to the coloured 

 edges of the oblique stripes which occur in most 

 of the species of the genus Sphinx. It has already 

 been insisted upon in a previous section, that the 

 mode in which this character originates negatives 

 the assumption of a phyletic force, because these 

 coloured edges are gradually built up out of irre- 

 gularly scattered spots. There is no occasion for 

 a " developmental force "to grope in the dark; 

 if such a power exists, we should expect that it 

 would add new characters to old ones with the 

 precision of a master workman. 



If, however, the coloured edges certainly depend 

 on natural selection, this agency causing .the 

 scattered spots to coalesce and become linear, we 



