6 The Mechanism of Evolution in Leptinotaesa 



in the substance itself, the other in the medium surrounding it — and the inter- 

 action of these two sets of factors determines the particular qualities, conditions,, 

 and attributes presented. In organisms there are both internal and external 

 factors, and the a priori view is that they have the same relation in organic 

 matter as in inorganic, and if they do not have this relation it is something to 

 be proved and not held as an a priori dogma. 



CATEGORIES OF ORGANIC CHARACTERISTICS. 



Present considerations of the characteristics of organisms designating them 

 all " characters," without in any respect attempting to comprehend what the 

 nature and cause of the character is, and how modifications may be the product 

 of diverse causes, have lead to much confusion. 



In physical terms natural specific things have three grades of characteristics : 



Specific Properties or Qualities — Belonging to substances, and not capable of 

 change without change in the nature of the substance except by alteration of the 

 factors of composition; i. e., color, hardness, specific gravity, configuration of 

 the system (crystallization). 



Attributes. — Characters distinguishing bodies of the same kind, as size, 

 weight, volume. 



Conditions. — States of being or activity, as temperature, motion, etc., that 

 can be changed or removed without altering the attributes or specific properties. 



In organisms there is precisely the same series of categories of characters 

 present, which must be considered in the investigation of the evolution phe- 

 nomena, and care taken that the three categories of characters are not confused 

 in investigation. 



SPECIFIC PROPERTIES OR QUALITIES. 



Specific properties or qualities are those characters which can not be changed 

 without altering the identity of the substance, and in the non-living this is 

 always accomplished in one of three ways, either by replacement within the sys- 

 tem of some factor that is productive of specific end-results, because of its pres- 

 ence, by another similar but different factor which is capable of occupying in the 

 system the position vacated by the displaced factor — a simple metathetic change ; 

 or change is produced by the loss of a factor, so that the character is no longer 

 produced ; and lastly, changes are produced by the production of new, or changes 

 in present, factors, thereby productive of new or transmuted characters in the 

 substance. This is precisely what happens in the non-living as in the living, 

 and I shall be able to show how in the materials that I have used there have been 

 produced in experiment permanent changes in the specific properties of these 

 organisms by these three main methods of change and by combinations of them. 

 In these modifications three general mechanisms of change can be distinguished : 



(1) Combinations, or the union into one of two or more factors or factorial 

 groups, producing in the end a combination product of the characters present 

 at the beginninff. 



(2) Decomposition or germinal disintegration, the breaking up of a sub- 

 stance or form in which there is loss of one or more of its factors and conse- 

 quently of one or more characters of the original, producing " varieties " of the 

 original. 



